diff --git a/parser/pom.xml b/parser/pom.xml
new file mode 100644
index 0000000..0ada699
--- /dev/null
+++ b/parser/pom.xml
@@ -0,0 +1,236 @@
+<!--
+  ~ Copyright 2016-present Open Networking Laboratory
+  ~
+  ~ Licensed under the Apache License, Version 2.0 (the "License");
+  ~ you may not use this file except in compliance with the License.
+  ~ You may obtain a copy of the License at
+  ~
+  ~     http://www.apache.org/licenses/LICENSE-2.0
+  ~
+  ~ Unless required by applicable law or agreed to in writing, software
+  ~ distributed under the License is distributed on an "AS IS" BASIS,
+  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  ~ See the License for the specific language governing permissions and
+  ~ limitations under the License.
+  -->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>org.onosproject</groupId>
+        <artifactId>onos-yang-tools</artifactId>
+        <version>1.9-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>onos-yang-utils-parser</artifactId>
+    <version>1.9-SNAPSHOT</version>
+    <packaging>maven-plugin</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.onosproject</groupId>
+            <artifactId>onos-yang-datamodel</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.onosproject</groupId>
+            <artifactId>onos-yang-utils-generator</artifactId>
+            <version>${project.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-core</artifactId>
+            <version>3.3.9</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-plugin-api</artifactId>
+            <version>3.3.9</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven.plugin-tools</groupId>
+            <artifactId>maven-plugin-annotations</artifactId>
+            <version>3.4</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.felix</groupId>
+            <artifactId>maven-scr-plugin</artifactId>
+            <version>1.21.0</version>
+            <scope>compile</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-artifact</artifactId>
+            <version>3.3.9</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-project</artifactId>
+            <version>3.0-alpha-2</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-model</artifactId>
+            <version>3.3.9</version>
+        </dependency>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.12</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.sonatype.plexus</groupId>
+            <artifactId>plexus-build-api</artifactId>
+            <version>0.0.7</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>2.4</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.hamcrest</groupId>
+            <artifactId>hamcrest-all</artifactId>
+            <version>1.3</version>
+        </dependency>
+        <dependency>
+            <groupId>org.antlr</groupId>
+            <artifactId>antlr4-runtime</artifactId>
+            <version>4.5.3</version>
+        </dependency>
+        <dependency>
+            <groupId>org.codehaus.mojo</groupId>
+            <artifactId>build-helper-maven-plugin</artifactId>
+            <version>1.10</version>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>1.7.21</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.antlr</groupId>
+                <artifactId>antlr4-maven-plugin</artifactId>
+                <version>4.5</version>
+                <executions>
+                    <execution>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>antlr4</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <sourceDirectory>src/main/resources</sourceDirectory>
+                    <outputDirectory>
+                        target/generated-sources/org/onosproject/yangutils/parser/antlrgencode
+                    </outputDirectory>
+                    <visitor>false</visitor>
+                    <listener>true</listener>
+                </configuration>
+            </plugin>
+            <plugin>
+                <artifactId>maven-clean-plugin</artifactId>
+                <version>3.0.0</version>
+                <executions>
+                    <execution>
+                        <id>Deleting auto-generated listener interfaces</id>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>clean</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <excludeDefaultDirectories>true</excludeDefaultDirectories>
+                    <filesets>
+                        <fileset>
+                            <directory>target</directory>
+                            <followSymlinks>false</followSymlinks>
+                            <useDefaultExcludes>true</useDefaultExcludes>
+                            <excludes>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangLexer.java
+                                </exclude>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/GeneratedYang.tokens
+                                </exclude>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangParser.java
+                                </exclude>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangLexer.tokens
+                                </exclude>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/YangLexer.java
+                                </exclude>
+                                <exclude>
+                                    **/generated-sources/org/onosproject/yangutils/parser/antlrgencode/YangLexer.tokens
+                                </exclude>
+                            </excludes>
+                        </fileset>
+                    </filesets>
+                    <verbose>false</verbose>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>build-helper-maven-plugin</artifactId>
+                <version>1.10</version>
+                <executions>
+                    <execution>
+                        <id>add-source</id>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>add-source</goal>
+                        </goals>
+                        <configuration>
+                            <sources>
+                                <source>
+                                    target/generated-sources/org/onosproject/yangutils/parser/antlrgencode
+                                </source>
+                                <sourceDirectory>
+                                    target/generated-sources/org/onosproject/yangutils/parser/antlrgencode
+                                </sourceDirectory>
+                            </sources>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-plugin-plugin</artifactId>
+                <version>3.4</version>
+                <configuration>
+                    <skipErrorNoDescriptorsFound>true
+                    </skipErrorNoDescriptorsFound>
+                </configuration>
+                <executions>
+                    <execution>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>descriptor</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.felix</groupId>
+                <artifactId>maven-bundle-plugin</artifactId>
+                <version>2.5.4</version>
+                <extensions>true</extensions>
+            </plugin>
+        </plugins>
+    </build>
+</project>
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/YangUtilsParser.java b/parser/src/main/java/org/onosproject/yangutils/parser/YangUtilsParser.java
new file mode 100644
index 0000000..ba119f6
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/YangUtilsParser.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser;
+
+import java.io.IOException;
+
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+
+/**
+ * Abstraction of entity which provides parser service of YANG files for yangutils-maven-plugin.
+ */
+public interface YangUtilsParser {
+
+    /**
+     * Returns the data model node. It is an entry function to initiate the YANG file parsing.
+     *
+     * @param file input YANG file
+     * @return YangNode root node of the data model tree
+     * @throws ParserException when fails to get the data model
+     * @throws IOException when there is an exception in IO operation
+     */
+    YangNode getDataModel(String file) throws IOException, ParserException;
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java
new file mode 100644
index 0000000..72e7995
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java
@@ -0,0 +1,1940 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Generated from GeneratedYang.g4 by ANTLR 4.5
+
+package org.onosproject.yangutils.parser.antlrgencode;
+
+import org.antlr.v4.runtime.tree.ParseTreeListener;
+
+/**
+ * Represents ANTLR interfaces to be implemented by listener to traverse the parse tree.
+ */
+public interface GeneratedYangListener extends ParseTreeListener {
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule yangfile.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterYangfile(GeneratedYangParser.YangfileContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule yangfile.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitYangfile(GeneratedYangParser.YangfileContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule moduleStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterModuleStatement(GeneratedYangParser.ModuleStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule moduleStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitModuleStatement(GeneratedYangParser.ModuleStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule moduleBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterModuleBody(GeneratedYangParser.ModuleBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule moduleBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitModuleBody(GeneratedYangParser.ModuleBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule moduleHeaderStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterModuleHeaderStatement(GeneratedYangParser.ModuleHeaderStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule moduleHeaderStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitModuleHeaderStatement(GeneratedYangParser.ModuleHeaderStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule linkageStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLinkageStatements(GeneratedYangParser.LinkageStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule linkageStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLinkageStatements(GeneratedYangParser.LinkageStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule metaStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMetaStatements(GeneratedYangParser.MetaStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule metaStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMetaStatements(GeneratedYangParser.MetaStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule revisionStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRevisionStatements(GeneratedYangParser.RevisionStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule revisionStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRevisionStatements(GeneratedYangParser.RevisionStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule bodyStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBodyStatements(GeneratedYangParser.BodyStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule bodyStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBodyStatements(GeneratedYangParser.BodyStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule yangVersionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterYangVersionStatement(GeneratedYangParser.YangVersionStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule yangVersionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitYangVersionStatement(GeneratedYangParser.YangVersionStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule namespaceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterNamespaceStatement(GeneratedYangParser.NamespaceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule namespaceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitNamespaceStatement(GeneratedYangParser.NamespaceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule prefixStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPrefixStatement(GeneratedYangParser.PrefixStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule prefixStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPrefixStatement(GeneratedYangParser.PrefixStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule importStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterImportStatement(GeneratedYangParser.ImportStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule importStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitImportStatement(GeneratedYangParser.ImportStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule importStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterImportStatementBody(GeneratedYangParser.ImportStatementBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule importStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitImportStatementBody(GeneratedYangParser.ImportStatementBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule revisionDateStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRevisionDateStatement(GeneratedYangParser.RevisionDateStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule revisionDateStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRevisionDateStatement(GeneratedYangParser.RevisionDateStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule includeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIncludeStatement(GeneratedYangParser.IncludeStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule includeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIncludeStatement(GeneratedYangParser.IncludeStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule organizationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterOrganizationStatement(GeneratedYangParser.OrganizationStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule organizationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitOrganizationStatement(GeneratedYangParser.OrganizationStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule contactStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterContactStatement(GeneratedYangParser.ContactStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule contactStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitContactStatement(GeneratedYangParser.ContactStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule descriptionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDescriptionStatement(GeneratedYangParser.DescriptionStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule descriptionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDescriptionStatement(GeneratedYangParser.DescriptionStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule referenceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterReferenceStatement(GeneratedYangParser.ReferenceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule referenceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitReferenceStatement(GeneratedYangParser.ReferenceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule revisionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRevisionStatement(GeneratedYangParser.RevisionStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule revisionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRevisionStatement(GeneratedYangParser.RevisionStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule revisionStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRevisionStatementBody(GeneratedYangParser.RevisionStatementBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule revisionStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRevisionStatementBody(GeneratedYangParser.RevisionStatementBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule subModuleStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterSubModuleStatement(GeneratedYangParser.SubModuleStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule subModuleStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitSubModuleStatement(GeneratedYangParser.SubModuleStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule submoduleBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterSubmoduleBody(GeneratedYangParser.SubmoduleBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule submoduleBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitSubmoduleBody(GeneratedYangParser.SubmoduleBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule submoduleHeaderStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterSubmoduleHeaderStatement(GeneratedYangParser.SubmoduleHeaderStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule submoduleHeaderStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitSubmoduleHeaderStatement(GeneratedYangParser.SubmoduleHeaderStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule belongstoStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBelongstoStatement(GeneratedYangParser.BelongstoStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule belongstoStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBelongstoStatement(GeneratedYangParser.BelongstoStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule belongstoStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBelongstoStatementBody(GeneratedYangParser.BelongstoStatementBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule belongstoStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBelongstoStatementBody(GeneratedYangParser.BelongstoStatementBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule extensionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterExtensionStatement(GeneratedYangParser.ExtensionStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule extensionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitExtensionStatement(GeneratedYangParser.ExtensionStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule extensionBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterExtensionBody(GeneratedYangParser.ExtensionBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule extensionBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitExtensionBody(GeneratedYangParser.ExtensionBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule argumentStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterArgumentStatement(GeneratedYangParser.ArgumentStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule argumentStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitArgumentStatement(GeneratedYangParser.ArgumentStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule argumentBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterArgumentBody(GeneratedYangParser.ArgumentBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule argumentBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitArgumentBody(GeneratedYangParser.ArgumentBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule yinElementStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterYinElementStatement(GeneratedYangParser.YinElementStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule yinElementStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitYinElementStatement(GeneratedYangParser.YinElementStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule identityStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIdentityStatement(GeneratedYangParser.IdentityStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule identityStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIdentityStatement(GeneratedYangParser.IdentityStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule identityBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIdentityBody(GeneratedYangParser.IdentityBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule identityBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIdentityBody(GeneratedYangParser.IdentityBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule baseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBaseStatement(GeneratedYangParser.BaseStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule baseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBaseStatement(GeneratedYangParser.BaseStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule featureStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterFeatureStatement(GeneratedYangParser.FeatureStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule featureStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitFeatureStatement(GeneratedYangParser.FeatureStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule featureBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterFeatureBody(GeneratedYangParser.FeatureBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule featureBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitFeatureBody(GeneratedYangParser.FeatureBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule dataDefStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDataDefStatement(GeneratedYangParser.DataDefStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule dataDefStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDataDefStatement(GeneratedYangParser.DataDefStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule ifFeatureStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIfFeatureStatement(GeneratedYangParser.IfFeatureStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule ifFeatureStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIfFeatureStatement(GeneratedYangParser.IfFeatureStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule unitsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUnitsStatement(GeneratedYangParser.UnitsStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule unitsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUnitsStatement(GeneratedYangParser.UnitsStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule typedefStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterTypedefStatement(GeneratedYangParser.TypedefStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule typedefStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitTypedefStatement(GeneratedYangParser.TypedefStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule typeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterTypeStatement(GeneratedYangParser.TypeStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule typeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitTypeStatement(GeneratedYangParser.TypeStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule typeBodyStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterTypeBodyStatements(GeneratedYangParser.TypeBodyStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule typeBodyStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitTypeBodyStatements(GeneratedYangParser.TypeBodyStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDecimal64Specification(GeneratedYangParser.Decimal64SpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDecimal64Specification(GeneratedYangParser.Decimal64SpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterFractionDigitStatement(GeneratedYangParser.FractionDigitStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule
+     * numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitFractionDigitStatement(GeneratedYangParser.FractionDigitStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule
+     * numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterNumericalRestrictions(GeneratedYangParser.NumericalRestrictionsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule numericalRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitNumericalRestrictions(GeneratedYangParser.NumericalRestrictionsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule rangeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRangeStatement(GeneratedYangParser.RangeStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule rangeStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRangeStatement(GeneratedYangParser.RangeStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule commonStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterCommonStatements(GeneratedYangParser.CommonStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule commonStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitCommonStatements(GeneratedYangParser.CommonStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule stringRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterStringRestrictions(GeneratedYangParser.StringRestrictionsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule stringRestrictions.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitStringRestrictions(GeneratedYangParser.StringRestrictionsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule lengthStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLengthStatement(GeneratedYangParser.LengthStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule lengthStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLengthStatement(GeneratedYangParser.LengthStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule patternStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPatternStatement(GeneratedYangParser.PatternStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule patternStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPatternStatement(GeneratedYangParser.PatternStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule defaultStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDefaultStatement(GeneratedYangParser.DefaultStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule defaultStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDefaultStatement(GeneratedYangParser.DefaultStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule enumSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterEnumSpecification(GeneratedYangParser.EnumSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule enumSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitEnumSpecification(GeneratedYangParser.EnumSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule enumStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterEnumStatement(GeneratedYangParser.EnumStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule enumStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitEnumStatement(GeneratedYangParser.EnumStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule enumStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterEnumStatementBody(GeneratedYangParser.EnumStatementBodyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule enumStatementBody.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitEnumStatementBody(GeneratedYangParser.EnumStatementBodyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule leafrefSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLeafrefSpecification(GeneratedYangParser.LeafrefSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule leafrefSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLeafrefSpecification(GeneratedYangParser.LeafrefSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule pathStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPathStatement(GeneratedYangParser.PathStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule pathStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPathStatement(GeneratedYangParser.PathStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule requireInstanceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRequireInstanceStatement(GeneratedYangParser.RequireInstanceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule requireInstanceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRequireInstanceStatement(GeneratedYangParser.RequireInstanceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule instanceIdentifierSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterInstanceIdentifierSpecification(
+            GeneratedYangParser.InstanceIdentifierSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule instanceIdentifierSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitInstanceIdentifierSpecification(GeneratedYangParser.InstanceIdentifierSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule identityrefSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIdentityrefSpecification(GeneratedYangParser.IdentityrefSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule identityrefSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIdentityrefSpecification(GeneratedYangParser.IdentityrefSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule unionSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUnionSpecification(GeneratedYangParser.UnionSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule unionSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUnionSpecification(GeneratedYangParser.UnionSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule bitsSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBitsSpecification(GeneratedYangParser.BitsSpecificationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule bitsSpecification.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBitsSpecification(GeneratedYangParser.BitsSpecificationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule bitStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBitStatement(GeneratedYangParser.BitStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule bitStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBitStatement(GeneratedYangParser.BitStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule bitBodyStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterBitBodyStatement(GeneratedYangParser.BitBodyStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule bitBodyStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitBitBodyStatement(GeneratedYangParser.BitBodyStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule positionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPositionStatement(GeneratedYangParser.PositionStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule positionStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPositionStatement(GeneratedYangParser.PositionStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule statusStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterStatusStatement(GeneratedYangParser.StatusStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule statusStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitStatusStatement(GeneratedYangParser.StatusStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule configStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterConfigStatement(GeneratedYangParser.ConfigStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule configStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitConfigStatement(GeneratedYangParser.ConfigStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule mandatoryStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMandatoryStatement(GeneratedYangParser.MandatoryStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule mandatoryStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMandatoryStatement(GeneratedYangParser.MandatoryStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule presenceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPresenceStatement(GeneratedYangParser.PresenceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule presenceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPresenceStatement(GeneratedYangParser.PresenceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule orderedByStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterOrderedByStatement(GeneratedYangParser.OrderedByStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule orderedByStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitOrderedByStatement(GeneratedYangParser.OrderedByStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule mustStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMustStatement(GeneratedYangParser.MustStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule mustStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMustStatement(GeneratedYangParser.MustStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule errorMessageStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterErrorMessageStatement(GeneratedYangParser.ErrorMessageStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule errorMessageStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitErrorMessageStatement(GeneratedYangParser.ErrorMessageStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule errorAppTagStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterErrorAppTagStatement(GeneratedYangParser.ErrorAppTagStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule errorAppTagStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitErrorAppTagStatement(GeneratedYangParser.ErrorAppTagStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule minElementsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMinElementsStatement(GeneratedYangParser.MinElementsStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule minElementsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMinElementsStatement(GeneratedYangParser.MinElementsStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule maxElementsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMaxElementsStatement(GeneratedYangParser.MaxElementsStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule maxElementsStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMaxElementsStatement(GeneratedYangParser.MaxElementsStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule valueStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterValueStatement(GeneratedYangParser.ValueStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule valueStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitValueStatement(GeneratedYangParser.ValueStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule groupingStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterGroupingStatement(GeneratedYangParser.GroupingStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule groupingStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitGroupingStatement(GeneratedYangParser.GroupingStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule containerStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterContainerStatement(GeneratedYangParser.ContainerStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule containerStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitContainerStatement(GeneratedYangParser.ContainerStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule leafStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLeafStatement(GeneratedYangParser.LeafStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule leafStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLeafStatement(GeneratedYangParser.LeafStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule leafListStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLeafListStatement(GeneratedYangParser.LeafListStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule leafListStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLeafListStatement(GeneratedYangParser.LeafListStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule listStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterListStatement(GeneratedYangParser.ListStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule listStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitListStatement(GeneratedYangParser.ListStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule keyStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterKeyStatement(GeneratedYangParser.KeyStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule keyStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitKeyStatement(GeneratedYangParser.KeyStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule uniqueStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUniqueStatement(GeneratedYangParser.UniqueStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule uniqueStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUniqueStatement(GeneratedYangParser.UniqueStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule choiceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterChoiceStatement(GeneratedYangParser.ChoiceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule choiceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitChoiceStatement(GeneratedYangParser.ChoiceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule shortCaseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterShortCaseStatement(GeneratedYangParser.ShortCaseStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule shortCaseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitShortCaseStatement(GeneratedYangParser.ShortCaseStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule caseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterCaseStatement(GeneratedYangParser.CaseStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule caseStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitCaseStatement(GeneratedYangParser.CaseStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule anyxmlStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAnyxmlStatement(GeneratedYangParser.AnyxmlStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule anyxmlStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAnyxmlStatement(GeneratedYangParser.AnyxmlStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule usesStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUsesStatement(GeneratedYangParser.UsesStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule usesStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUsesStatement(GeneratedYangParser.UsesStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineStatement(GeneratedYangParser.RefineStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineStatement(GeneratedYangParser.RefineStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineContainerStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineContainerStatements(GeneratedYangParser.RefineContainerStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineContainerStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineContainerStatements(GeneratedYangParser.RefineContainerStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineLeafStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineLeafStatements(GeneratedYangParser.RefineLeafStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineLeafStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineLeafStatements(GeneratedYangParser.RefineLeafStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineLeafListStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineLeafListStatements(GeneratedYangParser.RefineLeafListStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineLeafListStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineLeafListStatements(GeneratedYangParser.RefineLeafListStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineListStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineListStatements(GeneratedYangParser.RefineListStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineListStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineListStatements(GeneratedYangParser.RefineListStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineChoiceStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineChoiceStatements(GeneratedYangParser.RefineChoiceStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineChoiceStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineChoiceStatements(GeneratedYangParser.RefineChoiceStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineCaseStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineCaseStatements(GeneratedYangParser.RefineCaseStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineCaseStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineCaseStatements(GeneratedYangParser.RefineCaseStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refineAnyxmlStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefineAnyxmlStatements(GeneratedYangParser.RefineAnyxmlStatementsContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refineAnyxmlStatements.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefineAnyxmlStatements(GeneratedYangParser.RefineAnyxmlStatementsContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule augmentStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAugmentStatement(GeneratedYangParser.AugmentStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule augmentStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAugmentStatement(GeneratedYangParser.AugmentStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule whenStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterWhenStatement(GeneratedYangParser.WhenStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule whenStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitWhenStatement(GeneratedYangParser.WhenStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule rpcStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRpcStatement(GeneratedYangParser.RpcStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule rpcStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRpcStatement(GeneratedYangParser.RpcStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule inputStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterInputStatement(GeneratedYangParser.InputStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule inputStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitInputStatement(GeneratedYangParser.InputStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule outputStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterOutputStatement(GeneratedYangParser.OutputStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule outputStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitOutputStatement(GeneratedYangParser.OutputStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule notificationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterNotificationStatement(GeneratedYangParser.NotificationStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule notificationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitNotificationStatement(GeneratedYangParser.NotificationStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviationStatement(GeneratedYangParser.DeviationStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviationStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviationStatement(GeneratedYangParser.DeviationStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviateNotSupportedStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviateNotSupportedStatement(GeneratedYangParser.DeviateNotSupportedStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviateNotSupportedStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviateNotSupportedStatement(GeneratedYangParser.DeviateNotSupportedStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviateAddStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviateAddStatement(GeneratedYangParser.DeviateAddStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviateAddStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviateAddStatement(GeneratedYangParser.DeviateAddStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviateDeleteStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviateDeleteStatement(GeneratedYangParser.DeviateDeleteStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviateDeleteStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviateDeleteStatement(GeneratedYangParser.DeviateDeleteStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviateReplaceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviateReplaceStatement(GeneratedYangParser.DeviateReplaceStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviateReplaceStatement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviateReplaceStatement(GeneratedYangParser.DeviateReplaceStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule string.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterString(GeneratedYangParser.StringContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule string.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitString(GeneratedYangParser.StringContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule identifier.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterIdentifier(GeneratedYangParser.IdentifierContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule identifier.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitIdentifier(GeneratedYangParser.IdentifierContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule version.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterVersion(GeneratedYangParser.VersionContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule version.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitVersion(GeneratedYangParser.VersionContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule range.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRange(GeneratedYangParser.RangeContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule range.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRange(GeneratedYangParser.RangeContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule dateArgumentString.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDateArgumentString(GeneratedYangParser.DateArgumentStringContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule dateArgumentString.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDateArgumentString(GeneratedYangParser.DateArgumentStringContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule length.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLength(GeneratedYangParser.LengthContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule length.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLength(GeneratedYangParser.LengthContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule path.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPath(GeneratedYangParser.PathContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule path.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPath(GeneratedYangParser.PathContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule position.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPosition(GeneratedYangParser.PositionContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule position.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPosition(GeneratedYangParser.PositionContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule status.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterStatus(GeneratedYangParser.StatusContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule status.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitStatus(GeneratedYangParser.StatusContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule config.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterConfig(GeneratedYangParser.ConfigContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule config.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitConfig(GeneratedYangParser.ConfigContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule mandatory.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMandatory(GeneratedYangParser.MandatoryContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule mandatory.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMandatory(GeneratedYangParser.MandatoryContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule ordered-by.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterOrderedBy(GeneratedYangParser.OrderedByContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule ordered-by.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitOrderedBy(GeneratedYangParser.OrderedByContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule min elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMinValue(GeneratedYangParser.MinValueContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule min elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMinValue(GeneratedYangParser.MinValueContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule  max elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMaxValue(GeneratedYangParser.MaxValueContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule max elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMaxValue(GeneratedYangParser.MaxValueContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule key.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterKey(GeneratedYangParser.KeyContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule key.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitKey(GeneratedYangParser.KeyContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule unique.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUnique(GeneratedYangParser.UniqueContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule unique.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUnique(GeneratedYangParser.UniqueContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule refine.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefine(GeneratedYangParser.RefineContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule refine.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefine(GeneratedYangParser.RefineContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAugment(GeneratedYangParser.AugmentContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAugment(GeneratedYangParser.AugmentContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterFraction(GeneratedYangParser.FractionContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitFraction(GeneratedYangParser.FractionContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviation(GeneratedYangParser.DeviationContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviation(GeneratedYangParser.DeviationContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterValue(GeneratedYangParser.ValueContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitValue(GeneratedYangParser.ValueContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule yang construct.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterYangConstruct(GeneratedYangParser.YangConstructContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule yang construct.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitYangConstruct(GeneratedYangParser.YangConstructContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule compiler annotation statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterCompilerAnnotationStatement(GeneratedYangParser.CompilerAnnotationStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule compiler annotation statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitCompilerAnnotationStatement(GeneratedYangParser.CompilerAnnotationStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule compiler annotation body statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterCompilerAnnotationBodyStatement(GeneratedYangParser.CompilerAnnotationBodyStatementContext
+                                                      currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule compiler annotation body statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitCompilerAnnotationBodyStatement(GeneratedYangParser.CompilerAnnotationBodyStatementContext
+                                                     currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule app data structure statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAppDataStructureStatement(GeneratedYangParser.AppDataStructureStatementContext
+                                                currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule app data structure statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAppDataStructureStatement(GeneratedYangParser.AppDataStructureStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule app data structure.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAppDataStructure(GeneratedYangParser.AppDataStructureContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule app data strcuture.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAppDataStructure(GeneratedYangParser.AppDataStructureContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule app extended statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAppExtendedStatement(GeneratedYangParser.AppExtendedStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule app extended statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAppExtendedStatement(GeneratedYangParser.AppExtendedStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule extended name.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterExtendedName(GeneratedYangParser.ExtendedNameContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule extended name.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitExtendedName(GeneratedYangParser.ExtendedNameContext currentContext);
+
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule
+     * data structure key statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDataStructureKeyStatement(GeneratedYangParser.DataStructureKeyStatementContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar rule
+     * data structure key statement.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDataStructureKeyStatement(GeneratedYangParser.DataStructureKeyStatementContext currentContext);
+
+    /**
+     * Enters a parse tree produced by GeneratedYangParser for grammar rule require instance.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRequireInstance(GeneratedYangParser.RequireInstanceContext currentContext);
+
+    /**
+     * Exits a parse tree produced by GeneratedYangParser for grammar require instance.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRequireInstance(GeneratedYangParser.RequireInstanceContext currentContext);
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/package-info.java
new file mode 100644
index 0000000..747974e
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/antlrgencode/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+/**
+ * ANTLR interfaces to be implemented by listener.
+ */
+package org.onosproject.yangutils.parser.antlrgencode;
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/ParserException.java b/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/ParserException.java
new file mode 100644
index 0000000..8edff52
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/ParserException.java
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.exceptions;
+
+/**
+ * Represents base class for exceptions in parser operations.
+ */
+public class ParserException extends RuntimeException {
+
+    private static final long serialVersionUID = 20160211L;
+    private transient int lineNumber;
+    private transient int charPositionInLine;
+    private transient String fileName;
+
+    /**
+     * Creates a new parser exception.
+     */
+    public ParserException() {
+        super();
+    }
+
+    /**
+     * Creates a new parser exception with given message.
+     *
+     * @param message the detail of exception in string
+     */
+    public ParserException(String message) {
+        super(message);
+    }
+
+    /**
+     * Creates a new parser exception from given message and cause.
+     *
+     * @param message the detail of exception in string
+     * @param cause   underlying cause of the error
+     */
+    public ParserException(final String message, final Throwable cause) {
+        super(message, cause);
+    }
+
+    /**
+     * Creates a new parser exception from cause.
+     *
+     * @param cause underlying cause of the error
+     */
+    public ParserException(final Throwable cause) {
+        super(cause);
+    }
+
+    /**
+     * Returns line number of the exception.
+     *
+     * @return line number of the exception
+     */
+    public int getLineNumber() {
+        return this.lineNumber;
+    }
+
+    /**
+     * Returns YANG file name of the exception.
+     *
+     * @return YANG file name of the exception
+     */
+    public String getFileName() {
+        return this.fileName;
+    }
+
+    /**
+     * Returns position of the exception.
+     *
+     * @return position of the exception
+     */
+    public int getCharPositionInLine() {
+        return this.charPositionInLine;
+    }
+
+    /**
+     * Sets line number of YANG file.
+     *
+     * @param line line number of YANG file
+     */
+    public void setLine(int line) {
+        this.lineNumber = line;
+    }
+
+    /**
+     * Sets position of exception.
+     *
+     * @param charPosition position of exception
+     */
+    public void setCharPosition(int charPosition) {
+        this.charPositionInLine = charPosition;
+    }
+
+    /**
+     * Sets file name in parser exception.
+     *
+     * @param fileName YANG file name
+     */
+    public void setFileName(String fileName) {
+        this.fileName = fileName;
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/package-info.java
new file mode 100644
index 0000000..ec36b0d
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/exceptions/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+/**
+ * Custom parser exceptions.
+ */
+package org.onosproject.yangutils.parser.exceptions;
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
new file mode 100644
index 0000000..4ca9c5a
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
@@ -0,0 +1,1711 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl;
+
+import java.util.Stack;
+
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.antlr.v4.runtime.tree.ErrorNode;
+import org.antlr.v4.runtime.tree.TerminalNode;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangListener;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.impl.listeners.AppDataStructureListener;
+import org.onosproject.yangutils.parser.impl.listeners.AppExtendedNameListener;
+import org.onosproject.yangutils.parser.impl.listeners.ArgumentListener;
+import org.onosproject.yangutils.parser.impl.listeners.AugmentListener;
+import org.onosproject.yangutils.parser.impl.listeners.BaseFileListener;
+import org.onosproject.yangutils.parser.impl.listeners.BaseListener;
+import org.onosproject.yangutils.parser.impl.listeners.BelongsToListener;
+import org.onosproject.yangutils.parser.impl.listeners.BitListener;
+import org.onosproject.yangutils.parser.impl.listeners.BitsListener;
+import org.onosproject.yangutils.parser.impl.listeners.CaseListener;
+import org.onosproject.yangutils.parser.impl.listeners.ChoiceListener;
+import org.onosproject.yangutils.parser.impl.listeners.CompilerAnnotationListener;
+import org.onosproject.yangutils.parser.impl.listeners.ConfigListener;
+import org.onosproject.yangutils.parser.impl.listeners.ContactListener;
+import org.onosproject.yangutils.parser.impl.listeners.ContainerListener;
+import org.onosproject.yangutils.parser.impl.listeners.DataStructureKeyListener;
+import org.onosproject.yangutils.parser.impl.listeners.Decimal64Listener;
+import org.onosproject.yangutils.parser.impl.listeners.DefaultListener;
+import org.onosproject.yangutils.parser.impl.listeners.DescriptionListener;
+import org.onosproject.yangutils.parser.impl.listeners.EnumListener;
+import org.onosproject.yangutils.parser.impl.listeners.EnumerationListener;
+import org.onosproject.yangutils.parser.impl.listeners.ErrorAppTagListener;
+import org.onosproject.yangutils.parser.impl.listeners.ErrorMessageListener;
+import org.onosproject.yangutils.parser.impl.listeners.ExtensionListener;
+import org.onosproject.yangutils.parser.impl.listeners.FeatureListener;
+import org.onosproject.yangutils.parser.impl.listeners.FractionDigitsListener;
+import org.onosproject.yangutils.parser.impl.listeners.GroupingListener;
+import org.onosproject.yangutils.parser.impl.listeners.IdentityListener;
+import org.onosproject.yangutils.parser.impl.listeners.IdentityrefListener;
+import org.onosproject.yangutils.parser.impl.listeners.IfFeatureListener;
+import org.onosproject.yangutils.parser.impl.listeners.ImportListener;
+import org.onosproject.yangutils.parser.impl.listeners.IncludeListener;
+import org.onosproject.yangutils.parser.impl.listeners.InputListener;
+import org.onosproject.yangutils.parser.impl.listeners.KeyListener;
+import org.onosproject.yangutils.parser.impl.listeners.LeafListListener;
+import org.onosproject.yangutils.parser.impl.listeners.LeafListener;
+import org.onosproject.yangutils.parser.impl.listeners.LeafrefListener;
+import org.onosproject.yangutils.parser.impl.listeners.LengthRestrictionListener;
+import org.onosproject.yangutils.parser.impl.listeners.ListListener;
+import org.onosproject.yangutils.parser.impl.listeners.MandatoryListener;
+import org.onosproject.yangutils.parser.impl.listeners.MaxElementsListener;
+import org.onosproject.yangutils.parser.impl.listeners.MinElementsListener;
+import org.onosproject.yangutils.parser.impl.listeners.ModuleListener;
+import org.onosproject.yangutils.parser.impl.listeners.MustListener;
+import org.onosproject.yangutils.parser.impl.listeners.NamespaceListener;
+import org.onosproject.yangutils.parser.impl.listeners.NotificationListener;
+import org.onosproject.yangutils.parser.impl.listeners.OrganizationListener;
+import org.onosproject.yangutils.parser.impl.listeners.OutputListener;
+import org.onosproject.yangutils.parser.impl.listeners.PathListener;
+import org.onosproject.yangutils.parser.impl.listeners.PatternRestrictionListener;
+import org.onosproject.yangutils.parser.impl.listeners.PositionListener;
+import org.onosproject.yangutils.parser.impl.listeners.PrefixListener;
+import org.onosproject.yangutils.parser.impl.listeners.PresenceListener;
+import org.onosproject.yangutils.parser.impl.listeners.RangeRestrictionListener;
+import org.onosproject.yangutils.parser.impl.listeners.ReferenceListener;
+import org.onosproject.yangutils.parser.impl.listeners.RequireInstanceListener;
+import org.onosproject.yangutils.parser.impl.listeners.RevisionDateListener;
+import org.onosproject.yangutils.parser.impl.listeners.RevisionListener;
+import org.onosproject.yangutils.parser.impl.listeners.RpcListener;
+import org.onosproject.yangutils.parser.impl.listeners.ShortCaseListener;
+import org.onosproject.yangutils.parser.impl.listeners.StatusListener;
+import org.onosproject.yangutils.parser.impl.listeners.SubModuleListener;
+import org.onosproject.yangutils.parser.impl.listeners.TypeDefListener;
+import org.onosproject.yangutils.parser.impl.listeners.TypeListener;
+import org.onosproject.yangutils.parser.impl.listeners.UnionListener;
+import org.onosproject.yangutils.parser.impl.listeners.UniqueListener;
+import org.onosproject.yangutils.parser.impl.listeners.UnitsListener;
+import org.onosproject.yangutils.parser.impl.listeners.UsesListener;
+import org.onosproject.yangutils.parser.impl.listeners.ValueListener;
+import org.onosproject.yangutils.parser.impl.listeners.VersionListener;
+import org.onosproject.yangutils.parser.impl.listeners.WhenListener;
+
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.handleUnsupportedYangConstruct;
+import static org.onosproject.yangutils.utils.UtilConstants.CURRENTLY_UNSUPPORTED;
+import static org.onosproject.yangutils.utils.UtilConstants.UNSUPPORTED_YANG_CONSTRUCT;
+
+/**
+ * Represents ANTLR generates parse-tree. ANTLR generates a parse-tree listener interface that responds to events
+ * triggered by the built-in tree walker. The methods in listener are just
+ * callbacks. This class implements listener interface and generates the
+ * corresponding data model tree.
+ */
+public class TreeWalkListener implements GeneratedYangListener {
+
+    // List of parsable node entries maintained in stack
+    private Stack<Parsable> parsedDataStack = new Stack<>();
+
+    // Parse tree root node
+    private YangNode rootNode;
+
+    // YANG file name.
+    private String fileName;
+
+    /**
+     * Parent depth of grouping count for any node.
+     */
+    private int groupingDepth;
+
+    /**
+     * Parent depth of unsupported yang construct count for any node.
+     */
+    private int unsupportedYangConstructDepth;
+
+    /**
+     * Returns number of unsupported yang constructs parents, by a node, at any level.
+     *
+     * @return depth of unsupported yang constructs
+     */
+    public int getUnsupportedYangConstructDepth() {
+        return unsupportedYangConstructDepth;
+    }
+
+    /**
+     * Sets number of unsupported yang constructs by a node at any level.
+     */
+    private void increaseUnsupportedYangConstructDepth() {
+        unsupportedYangConstructDepth++;
+    }
+
+    /**
+     * Sets number of unsupported yang constructs by a node at any level.
+     */
+    private void decreaseUnsupportedYangConstructDepth() {
+        unsupportedYangConstructDepth--;
+    }
+
+    /**
+     * Returns number of grouping parents, by a node, at any level.
+     *
+     * @return depth of grouping
+     */
+    public int getGroupingDepth() {
+        return groupingDepth;
+    }
+
+    /**
+     * Sets number of grouping parents by a node at any level.
+     */
+    public void increaseGroupingDepth() {
+        groupingDepth++;
+    }
+
+    /**
+     * Sets number of grouping parents by a node at any level.
+     */
+    public void decreaseGroupingDepth() {
+        groupingDepth--;
+    }
+
+    /**
+     * Returns stack of parsable data.
+     *
+     * @return stack of parsable data
+     */
+    public Stack<Parsable> getParsedDataStack() {
+        return parsedDataStack;
+    }
+
+    /**
+     * Returns root node.
+     *
+     * @return rootNode of data model tree
+     */
+    public YangNode getRootNode() {
+        return rootNode;
+    }
+
+    /**
+     * Returns YANG file name.
+     *
+     * @return YANG file name
+     */
+    public String getFileName() {
+        return fileName;
+    }
+
+    /**
+     * Sets YANG file name.
+     *
+     * @param fileName YANG file name
+     */
+    public void setFileName(String fileName) {
+        this.fileName = fileName;
+    }
+
+    /**
+     * Set parsed data stack.
+     *
+     * @param parsedDataStack stack of parsable data objects
+     */
+    public void setParsedDataStack(Stack<Parsable> parsedDataStack) {
+        this.parsedDataStack = parsedDataStack;
+    }
+
+    /**
+     * Set root node.
+     *
+     * @param rootNode root node of data model tree
+     */
+    public void setRootNode(YangNode rootNode) {
+        this.rootNode = rootNode;
+    }
+
+    @Override
+    public void enterYangfile(GeneratedYangParser.YangfileContext ctx) {
+        BaseFileListener.processYangFileEntry(this, ctx);
+    }
+
+    @Override
+    public void exitYangfile(GeneratedYangParser.YangfileContext ctx) {
+        BaseFileListener.processYangFileExit(this, ctx);
+    }
+
+    @Override
+    public void enterModuleStatement(GeneratedYangParser.ModuleStatementContext ctx) {
+        ModuleListener.processModuleEntry(this, ctx);
+    }
+
+    @Override
+    public void exitModuleStatement(GeneratedYangParser.ModuleStatementContext ctx) {
+        ModuleListener.processModuleExit(this, ctx);
+    }
+
+    @Override
+    public void enterModuleBody(GeneratedYangParser.ModuleBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitModuleBody(GeneratedYangParser.ModuleBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterModuleHeaderStatement(GeneratedYangParser.ModuleHeaderStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitModuleHeaderStatement(GeneratedYangParser.ModuleHeaderStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterLinkageStatements(GeneratedYangParser.LinkageStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitLinkageStatements(GeneratedYangParser.LinkageStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMetaStatements(GeneratedYangParser.MetaStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitMetaStatements(GeneratedYangParser.MetaStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRevisionStatements(GeneratedYangParser.RevisionStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRevisionStatements(GeneratedYangParser.RevisionStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterBodyStatements(GeneratedYangParser.BodyStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitBodyStatements(GeneratedYangParser.BodyStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterYangVersionStatement(GeneratedYangParser.YangVersionStatementContext ctx) {
+        VersionListener.processVersionEntry(this, ctx);
+    }
+
+    @Override
+    public void exitYangVersionStatement(GeneratedYangParser.YangVersionStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterNamespaceStatement(GeneratedYangParser.NamespaceStatementContext ctx) {
+        NamespaceListener.processNamespaceEntry(this, ctx);
+    }
+
+    @Override
+    public void exitNamespaceStatement(GeneratedYangParser.NamespaceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterPrefixStatement(GeneratedYangParser.PrefixStatementContext ctx) {
+        PrefixListener.processPrefixEntry(this, ctx);
+    }
+
+    @Override
+    public void exitPrefixStatement(GeneratedYangParser.PrefixStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterImportStatement(GeneratedYangParser.ImportStatementContext ctx) {
+        ImportListener.processImportEntry(this, ctx);
+    }
+
+    @Override
+    public void exitImportStatement(GeneratedYangParser.ImportStatementContext ctx) {
+        ImportListener.processImportExit(this, ctx);
+    }
+
+    @Override
+    public void enterImportStatementBody(GeneratedYangParser.ImportStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitImportStatementBody(GeneratedYangParser.ImportStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRevisionDateStatement(GeneratedYangParser.RevisionDateStatementContext ctx) {
+        RevisionDateListener.processRevisionDateEntry(this, ctx);
+    }
+
+    @Override
+    public void exitRevisionDateStatement(GeneratedYangParser.RevisionDateStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterIncludeStatement(GeneratedYangParser.IncludeStatementContext ctx) {
+        IncludeListener.processIncludeEntry(this, ctx);
+    }
+
+    @Override
+    public void exitIncludeStatement(GeneratedYangParser.IncludeStatementContext ctx) {
+        IncludeListener.processIncludeExit(this, ctx);
+    }
+
+    @Override
+    public void enterOrganizationStatement(GeneratedYangParser.OrganizationStatementContext ctx) {
+        OrganizationListener.processOrganizationEntry(this, ctx);
+    }
+
+    @Override
+    public void exitOrganizationStatement(GeneratedYangParser.OrganizationStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterContactStatement(GeneratedYangParser.ContactStatementContext ctx) {
+        ContactListener.processContactEntry(this, ctx);
+    }
+
+    @Override
+    public void exitContactStatement(GeneratedYangParser.ContactStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDescriptionStatement(GeneratedYangParser.DescriptionStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            DescriptionListener.processDescriptionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitDescriptionStatement(GeneratedYangParser.DescriptionStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterReferenceStatement(GeneratedYangParser.ReferenceStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            ReferenceListener.processReferenceEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitReferenceStatement(GeneratedYangParser.ReferenceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRevisionStatement(GeneratedYangParser.RevisionStatementContext ctx) {
+        RevisionListener.processRevisionEntry(this, ctx);
+    }
+
+    @Override
+    public void exitRevisionStatement(GeneratedYangParser.RevisionStatementContext ctx) {
+        RevisionListener.processRevisionExit(this, ctx);
+    }
+
+    @Override
+    public void enterRevisionStatementBody(GeneratedYangParser.RevisionStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRevisionStatementBody(GeneratedYangParser.RevisionStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterSubModuleStatement(GeneratedYangParser.SubModuleStatementContext ctx) {
+        SubModuleListener.processSubModuleEntry(this, ctx);
+    }
+
+    @Override
+    public void exitSubModuleStatement(GeneratedYangParser.SubModuleStatementContext ctx) {
+        SubModuleListener.processSubModuleExit(this, ctx);
+    }
+
+    @Override
+    public void enterSubmoduleBody(GeneratedYangParser.SubmoduleBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitSubmoduleBody(GeneratedYangParser.SubmoduleBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterSubmoduleHeaderStatement(GeneratedYangParser.SubmoduleHeaderStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitSubmoduleHeaderStatement(GeneratedYangParser.SubmoduleHeaderStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterBelongstoStatement(GeneratedYangParser.BelongstoStatementContext ctx) {
+        BelongsToListener.processBelongsToEntry(this, ctx);
+    }
+
+    @Override
+    public void exitBelongstoStatement(GeneratedYangParser.BelongstoStatementContext ctx) {
+        BelongsToListener.processBelongsToExit(this, ctx);
+    }
+
+    @Override
+    public void enterBelongstoStatementBody(GeneratedYangParser.BelongstoStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitBelongstoStatementBody(GeneratedYangParser.BelongstoStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterExtensionStatement(GeneratedYangParser.ExtensionStatementContext ctx) {
+        ExtensionListener.processExtensionEntry(this, ctx);
+    }
+
+    @Override
+    public void exitExtensionStatement(GeneratedYangParser.ExtensionStatementContext ctx) {
+        ExtensionListener.processExtensionExit(this, ctx);
+    }
+
+    @Override
+    public void enterExtensionBody(GeneratedYangParser.ExtensionBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitExtensionBody(GeneratedYangParser.ExtensionBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterArgumentStatement(GeneratedYangParser.ArgumentStatementContext ctx) {
+        ArgumentListener.processArgumentEntry(this, ctx);
+    }
+
+    @Override
+    public void exitArgumentStatement(GeneratedYangParser.ArgumentStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterArgumentBody(GeneratedYangParser.ArgumentBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitArgumentBody(GeneratedYangParser.ArgumentBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterYinElementStatement(GeneratedYangParser.YinElementStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitYinElementStatement(GeneratedYangParser.YinElementStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterIdentityStatement(GeneratedYangParser.IdentityStatementContext ctx) {
+        IdentityListener.processIdentityEntry(this, ctx);
+    }
+
+    @Override
+    public void exitIdentityStatement(GeneratedYangParser.IdentityStatementContext ctx) {
+        IdentityListener.processIdentityExit(this, ctx);
+    }
+
+    @Override
+    public void enterIdentityBody(GeneratedYangParser.IdentityBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitIdentityBody(GeneratedYangParser.IdentityBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterBaseStatement(GeneratedYangParser.BaseStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            BaseListener.processBaseEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitBaseStatement(GeneratedYangParser.BaseStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterFeatureStatement(GeneratedYangParser.FeatureStatementContext ctx) {
+        FeatureListener.processFeatureEntry(this, ctx);
+    }
+
+    @Override
+    public void exitFeatureStatement(GeneratedYangParser.FeatureStatementContext ctx) {
+        FeatureListener.processFeatureExit(this, ctx);
+    }
+
+    @Override
+    public void enterFeatureBody(GeneratedYangParser.FeatureBodyContext ctx) {
+        // do nothing
+    }
+
+    @Override
+    public void exitFeatureBody(GeneratedYangParser.FeatureBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDataDefStatement(GeneratedYangParser.DataDefStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDataDefStatement(GeneratedYangParser.DataDefStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterIfFeatureStatement(GeneratedYangParser.IfFeatureStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            IfFeatureListener.processIfFeatureEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitIfFeatureStatement(GeneratedYangParser.IfFeatureStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterUnitsStatement(GeneratedYangParser.UnitsStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            UnitsListener.processUnitsEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitUnitsStatement(GeneratedYangParser.UnitsStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterTypedefStatement(GeneratedYangParser.TypedefStatementContext ctx) {
+        TypeDefListener.processTypeDefEntry(this, ctx);
+    }
+
+    @Override
+    public void exitTypedefStatement(GeneratedYangParser.TypedefStatementContext ctx) {
+        TypeDefListener.processTypeDefExit(this, ctx);
+    }
+
+    @Override
+    public void enterTypeStatement(GeneratedYangParser.TypeStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            TypeListener.processTypeEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitTypeStatement(GeneratedYangParser.TypeStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            TypeListener.processTypeExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterTypeBodyStatements(GeneratedYangParser.TypeBodyStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitTypeBodyStatements(GeneratedYangParser.TypeBodyStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDecimal64Specification(GeneratedYangParser.Decimal64SpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            Decimal64Listener.processDecimal64Entry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitDecimal64Specification(GeneratedYangParser.Decimal64SpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            Decimal64Listener.processDecimal64Exit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterFractionDigitStatement(GeneratedYangParser.FractionDigitStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            FractionDigitsListener.processFractionDigitsEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitFractionDigitStatement(GeneratedYangParser.FractionDigitStatementContext currentContext) {
+        // do nothing
+    }
+
+    @Override
+    public void enterNumericalRestrictions(GeneratedYangParser.NumericalRestrictionsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitNumericalRestrictions(GeneratedYangParser.NumericalRestrictionsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRangeStatement(GeneratedYangParser.RangeStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            RangeRestrictionListener.processRangeRestrictionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitRangeStatement(GeneratedYangParser.RangeStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            RangeRestrictionListener.processRangeRestrictionExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterCommonStatements(GeneratedYangParser.CommonStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitCommonStatements(GeneratedYangParser.CommonStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterStringRestrictions(GeneratedYangParser.StringRestrictionsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitStringRestrictions(GeneratedYangParser.StringRestrictionsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterLengthStatement(GeneratedYangParser.LengthStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            LengthRestrictionListener.processLengthRestrictionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitLengthStatement(GeneratedYangParser.LengthStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            LengthRestrictionListener.processLengthRestrictionExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterPatternStatement(GeneratedYangParser.PatternStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            PatternRestrictionListener.processPatternRestrictionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitPatternStatement(GeneratedYangParser.PatternStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            PatternRestrictionListener.processPatternRestrictionExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterDefaultStatement(GeneratedYangParser.DefaultStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            DefaultListener.processDefaultEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitDefaultStatement(GeneratedYangParser.DefaultStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterEnumSpecification(GeneratedYangParser.EnumSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            EnumerationListener.processEnumerationEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitEnumSpecification(GeneratedYangParser.EnumSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            EnumerationListener.processEnumerationExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterEnumStatement(GeneratedYangParser.EnumStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            EnumListener.processEnumEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitEnumStatement(GeneratedYangParser.EnumStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            EnumListener.processEnumExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterEnumStatementBody(GeneratedYangParser.EnumStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitEnumStatementBody(GeneratedYangParser.EnumStatementBodyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterLeafrefSpecification(GeneratedYangParser.LeafrefSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            LeafrefListener.processLeafrefEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitLeafrefSpecification(GeneratedYangParser.LeafrefSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            LeafrefListener.processLeafrefExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterPathStatement(GeneratedYangParser.PathStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            PathListener.processPathEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitPathStatement(GeneratedYangParser.PathStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRequireInstanceStatement(GeneratedYangParser.RequireInstanceStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            RequireInstanceListener.processRequireInstanceEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitRequireInstanceStatement(GeneratedYangParser.RequireInstanceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterInstanceIdentifierSpecification(GeneratedYangParser.InstanceIdentifierSpecificationContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitInstanceIdentifierSpecification(GeneratedYangParser.InstanceIdentifierSpecificationContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterIdentityrefSpecification(GeneratedYangParser.IdentityrefSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            IdentityrefListener.processIdentityrefEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitIdentityrefSpecification(GeneratedYangParser.IdentityrefSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            IdentityrefListener.processIdentityrefExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterUnionSpecification(GeneratedYangParser.UnionSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            UnionListener.processUnionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitUnionSpecification(GeneratedYangParser.UnionSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            UnionListener.processUnionExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterBitsSpecification(GeneratedYangParser.BitsSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            BitsListener.processBitsEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitBitsSpecification(GeneratedYangParser.BitsSpecificationContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            BitsListener.processBitsExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterBitStatement(GeneratedYangParser.BitStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            BitListener.processBitEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitBitStatement(GeneratedYangParser.BitStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            BitListener.processBitExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterBitBodyStatement(GeneratedYangParser.BitBodyStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitBitBodyStatement(GeneratedYangParser.BitBodyStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterPositionStatement(GeneratedYangParser.PositionStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            PositionListener.processPositionEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitPositionStatement(GeneratedYangParser.PositionStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterStatusStatement(GeneratedYangParser.StatusStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            StatusListener.processStatusEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitStatusStatement(GeneratedYangParser.StatusStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterConfigStatement(GeneratedYangParser.ConfigStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            ConfigListener.processConfigEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitConfigStatement(GeneratedYangParser.ConfigStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMandatoryStatement(GeneratedYangParser.MandatoryStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            MandatoryListener.processMandatoryEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitMandatoryStatement(GeneratedYangParser.MandatoryStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterPresenceStatement(GeneratedYangParser.PresenceStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            PresenceListener.processPresenceEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitPresenceStatement(GeneratedYangParser.PresenceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterOrderedByStatement(GeneratedYangParser.OrderedByStatementContext ctx) {
+        handleUnsupportedYangConstruct(YangConstructType.ORDERED_BY_DATA, ctx, CURRENTLY_UNSUPPORTED, getFileName());
+    }
+
+    @Override
+    public void exitOrderedByStatement(GeneratedYangParser.OrderedByStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMustStatement(GeneratedYangParser.MustStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            MustListener.processMustEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitMustStatement(GeneratedYangParser.MustStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            MustListener.processMustExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterErrorMessageStatement(GeneratedYangParser.ErrorMessageStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            ErrorMessageListener.processErrorMessageEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitErrorMessageStatement(GeneratedYangParser.ErrorMessageStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterErrorAppTagStatement(GeneratedYangParser.ErrorAppTagStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            ErrorAppTagListener.processErrorAppTagMessageEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitErrorAppTagStatement(GeneratedYangParser.ErrorAppTagStatementContext ctx) {
+        //do nothing
+    }
+
+    @Override
+    public void enterMinElementsStatement(GeneratedYangParser.MinElementsStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            MinElementsListener.processMinElementsEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitMinElementsStatement(GeneratedYangParser.MinElementsStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMaxElementsStatement(GeneratedYangParser.MaxElementsStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            MaxElementsListener.processMaxElementsEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitMaxElementsStatement(GeneratedYangParser.MaxElementsStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterValueStatement(GeneratedYangParser.ValueStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            ValueListener.processValueEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitValueStatement(GeneratedYangParser.ValueStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterGroupingStatement(GeneratedYangParser.GroupingStatementContext ctx) {
+        GroupingListener.processGroupingEntry(this, ctx);
+    }
+
+    @Override
+    public void exitGroupingStatement(GeneratedYangParser.GroupingStatementContext ctx) {
+        GroupingListener.processGroupingExit(this, ctx);
+    }
+
+    @Override
+    public void enterContainerStatement(GeneratedYangParser.ContainerStatementContext ctx) {
+        ContainerListener.processContainerEntry(this, ctx);
+    }
+
+    @Override
+    public void exitContainerStatement(GeneratedYangParser.ContainerStatementContext ctx) {
+        ContainerListener.processContainerExit(this, ctx);
+    }
+
+    @Override
+    public void enterLeafStatement(GeneratedYangParser.LeafStatementContext ctx) {
+        LeafListener.processLeafEntry(this, ctx);
+    }
+
+    @Override
+    public void exitLeafStatement(GeneratedYangParser.LeafStatementContext ctx) {
+        LeafListener.processLeafExit(this, ctx);
+    }
+
+    @Override
+    public void enterLeafListStatement(GeneratedYangParser.LeafListStatementContext ctx) {
+        LeafListListener.processLeafListEntry(this, ctx);
+    }
+
+    @Override
+    public void exitLeafListStatement(GeneratedYangParser.LeafListStatementContext ctx) {
+        LeafListListener.processLeafListExit(this, ctx);
+    }
+
+    @Override
+    public void enterListStatement(GeneratedYangParser.ListStatementContext ctx) {
+        ListListener.processListEntry(this, ctx);
+    }
+
+    @Override
+    public void exitListStatement(GeneratedYangParser.ListStatementContext ctx) {
+        ListListener.processListExit(this, ctx);
+    }
+
+    @Override
+    public void enterKeyStatement(GeneratedYangParser.KeyStatementContext ctx) {
+        KeyListener.processKeyEntry(this, ctx);
+    }
+
+    @Override
+    public void exitKeyStatement(GeneratedYangParser.KeyStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterUniqueStatement(GeneratedYangParser.UniqueStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            UniqueListener.processUniqueEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitUniqueStatement(GeneratedYangParser.UniqueStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterChoiceStatement(GeneratedYangParser.ChoiceStatementContext ctx) {
+        ChoiceListener.processChoiceEntry(this, ctx);
+    }
+
+    @Override
+    public void exitChoiceStatement(GeneratedYangParser.ChoiceStatementContext ctx) {
+        ChoiceListener.processChoiceExit(this, ctx);
+    }
+
+    @Override
+    public void enterShortCaseStatement(GeneratedYangParser.ShortCaseStatementContext ctx) {
+        ShortCaseListener.processShortCaseEntry(this, ctx);
+    }
+
+    @Override
+    public void exitShortCaseStatement(GeneratedYangParser.ShortCaseStatementContext ctx) {
+        ShortCaseListener.processShortCaseExit(this, ctx);
+    }
+
+    @Override
+    public void enterCaseStatement(GeneratedYangParser.CaseStatementContext ctx) {
+        CaseListener.processCaseEntry(this, ctx);
+    }
+
+    @Override
+    public void exitCaseStatement(GeneratedYangParser.CaseStatementContext ctx) {
+        CaseListener.processCaseExit(this, ctx);
+    }
+
+    @Override
+    public void enterAnyxmlStatement(GeneratedYangParser.AnyxmlStatementContext ctx) {
+        increaseUnsupportedYangConstructDepth();
+        handleUnsupportedYangConstruct(YangConstructType.ANYXML_DATA, ctx, UNSUPPORTED_YANG_CONSTRUCT, getFileName());
+    }
+
+    @Override
+    public void exitAnyxmlStatement(GeneratedYangParser.AnyxmlStatementContext ctx) {
+        decreaseUnsupportedYangConstructDepth();
+    }
+
+    @Override
+    public void enterUsesStatement(GeneratedYangParser.UsesStatementContext ctx) {
+        UsesListener.processUsesEntry(this, ctx);
+    }
+
+    @Override
+    public void exitUsesStatement(GeneratedYangParser.UsesStatementContext ctx) {
+        UsesListener.processUsesExit(this, ctx);
+    }
+
+    @Override
+    public void enterRefineStatement(GeneratedYangParser.RefineStatementContext ctx) {
+        increaseUnsupportedYangConstructDepth();
+        handleUnsupportedYangConstruct(YangConstructType.REFINE_DATA, ctx, UNSUPPORTED_YANG_CONSTRUCT, getFileName());
+    }
+
+    @Override
+    public void exitRefineStatement(GeneratedYangParser.RefineStatementContext ctx) {
+        decreaseUnsupportedYangConstructDepth();
+    }
+
+    @Override
+    public void enterRefineContainerStatements(GeneratedYangParser.RefineContainerStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineContainerStatements(GeneratedYangParser.RefineContainerStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineLeafStatements(GeneratedYangParser.RefineLeafStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineLeafStatements(GeneratedYangParser.RefineLeafStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineLeafListStatements(GeneratedYangParser.RefineLeafListStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineLeafListStatements(GeneratedYangParser.RefineLeafListStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineListStatements(GeneratedYangParser.RefineListStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineListStatements(GeneratedYangParser.RefineListStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineChoiceStatements(GeneratedYangParser.RefineChoiceStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineChoiceStatements(GeneratedYangParser.RefineChoiceStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineCaseStatements(GeneratedYangParser.RefineCaseStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineCaseStatements(GeneratedYangParser.RefineCaseStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefineAnyxmlStatements(GeneratedYangParser.RefineAnyxmlStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefineAnyxmlStatements(GeneratedYangParser.RefineAnyxmlStatementsContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterAugmentStatement(GeneratedYangParser.AugmentStatementContext ctx) {
+        AugmentListener.processAugmentEntry(this, ctx);
+    }
+
+    @Override
+    public void exitAugmentStatement(GeneratedYangParser.AugmentStatementContext ctx) {
+        AugmentListener.processAugmentExit(this, ctx);
+    }
+
+    @Override
+    public void enterWhenStatement(GeneratedYangParser.WhenStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            WhenListener.processWhenEntry(this, ctx);
+        }
+    }
+
+    @Override
+    public void exitWhenStatement(GeneratedYangParser.WhenStatementContext ctx) {
+        if (getUnsupportedYangConstructDepth() == 0) {
+            WhenListener.processWhenExit(this, ctx);
+        }
+    }
+
+    @Override
+    public void enterRpcStatement(GeneratedYangParser.RpcStatementContext ctx) {
+        RpcListener.processRpcEntry(this, ctx);
+    }
+
+    @Override
+    public void exitRpcStatement(GeneratedYangParser.RpcStatementContext ctx) {
+        RpcListener.processRpcExit(this, ctx);
+    }
+
+    @Override
+    public void enterInputStatement(GeneratedYangParser.InputStatementContext ctx) {
+        InputListener.processInputEntry(this, ctx);
+    }
+
+    @Override
+    public void exitInputStatement(GeneratedYangParser.InputStatementContext ctx) {
+        InputListener.processInputExit(this, ctx);
+    }
+
+    @Override
+    public void enterOutputStatement(GeneratedYangParser.OutputStatementContext ctx) {
+        OutputListener.processOutputEntry(this, ctx);
+    }
+
+    @Override
+    public void exitOutputStatement(GeneratedYangParser.OutputStatementContext ctx) {
+        OutputListener.processOutputExit(this, ctx);
+    }
+
+    @Override
+    public void enterNotificationStatement(GeneratedYangParser.NotificationStatementContext ctx) {
+        NotificationListener.processNotificationEntry(this, ctx);
+    }
+
+    @Override
+    public void exitNotificationStatement(GeneratedYangParser.NotificationStatementContext ctx) {
+        NotificationListener.processNotificationExit(this, ctx);
+    }
+
+    @Override
+    public void enterDeviationStatement(GeneratedYangParser.DeviationStatementContext ctx) {
+        increaseUnsupportedYangConstructDepth();
+        handleUnsupportedYangConstruct(YangConstructType.DEVIATION_DATA, ctx, UNSUPPORTED_YANG_CONSTRUCT,
+                getFileName());
+    }
+
+    @Override
+    public void exitDeviationStatement(GeneratedYangParser.DeviationStatementContext ctx) {
+        decreaseUnsupportedYangConstructDepth();
+    }
+
+    @Override
+    public void enterDeviateNotSupportedStatement(GeneratedYangParser.DeviateNotSupportedStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDeviateNotSupportedStatement(GeneratedYangParser.DeviateNotSupportedStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDeviateAddStatement(GeneratedYangParser.DeviateAddStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDeviateAddStatement(GeneratedYangParser.DeviateAddStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDeviateDeleteStatement(GeneratedYangParser.DeviateDeleteStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDeviateDeleteStatement(GeneratedYangParser.DeviateDeleteStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDeviateReplaceStatement(GeneratedYangParser.DeviateReplaceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDeviateReplaceStatement(GeneratedYangParser.DeviateReplaceStatementContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterString(GeneratedYangParser.StringContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitString(GeneratedYangParser.StringContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterIdentifier(GeneratedYangParser.IdentifierContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitIdentifier(GeneratedYangParser.IdentifierContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDateArgumentString(GeneratedYangParser.DateArgumentStringContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDateArgumentString(GeneratedYangParser.DateArgumentStringContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRange(GeneratedYangParser.RangeContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRange(GeneratedYangParser.RangeContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterLength(GeneratedYangParser.LengthContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitLength(GeneratedYangParser.LengthContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterPath(GeneratedYangParser.PathContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitPath(GeneratedYangParser.PathContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterPosition(GeneratedYangParser.PositionContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitPosition(GeneratedYangParser.PositionContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterStatus(GeneratedYangParser.StatusContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitStatus(GeneratedYangParser.StatusContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterConfig(GeneratedYangParser.ConfigContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitConfig(GeneratedYangParser.ConfigContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMandatory(GeneratedYangParser.MandatoryContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitMandatory(GeneratedYangParser.MandatoryContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterOrderedBy(GeneratedYangParser.OrderedByContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitOrderedBy(GeneratedYangParser.OrderedByContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMinValue(GeneratedYangParser.MinValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitMinValue(GeneratedYangParser.MinValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterMaxValue(GeneratedYangParser.MaxValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitMaxValue(GeneratedYangParser.MaxValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterKey(GeneratedYangParser.KeyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitKey(GeneratedYangParser.KeyContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterUnique(GeneratedYangParser.UniqueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitUnique(GeneratedYangParser.UniqueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRefine(GeneratedYangParser.RefineContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRefine(GeneratedYangParser.RefineContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterAugment(GeneratedYangParser.AugmentContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitAugment(GeneratedYangParser.AugmentContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterDeviation(GeneratedYangParser.DeviationContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitDeviation(GeneratedYangParser.DeviationContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterYangConstruct(GeneratedYangParser.YangConstructContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitYangConstruct(GeneratedYangParser.YangConstructContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterCompilerAnnotationStatement(GeneratedYangParser.CompilerAnnotationStatementContext ctx) {
+        CompilerAnnotationListener.processCompilerAnnotationEntry(this, ctx);
+    }
+
+    @Override
+    public void exitCompilerAnnotationStatement(GeneratedYangParser.CompilerAnnotationStatementContext ctx) {
+        CompilerAnnotationListener.processCompilerAnnotationExit(this, ctx);
+    }
+
+    @Override
+    public void enterCompilerAnnotationBodyStatement(GeneratedYangParser.CompilerAnnotationBodyStatementContext ctx) {
+        // do nothing
+    }
+
+    @Override
+    public void exitCompilerAnnotationBodyStatement(GeneratedYangParser.CompilerAnnotationBodyStatementContext ctx) {
+        // do nothing
+    }
+
+    @Override
+    public void enterAppDataStructureStatement(GeneratedYangParser.AppDataStructureStatementContext ctx) {
+        AppDataStructureListener.processAppDataStructureEntry(this, ctx);
+    }
+
+    @Override
+    public void exitAppDataStructureStatement(GeneratedYangParser.AppDataStructureStatementContext ctx) {
+        AppDataStructureListener.processAppDataStructureExit(this, ctx);
+    }
+
+    @Override
+    public void enterAppDataStructure(GeneratedYangParser.AppDataStructureContext currentContext) {
+        // do nothing
+    }
+
+    @Override
+    public void exitAppDataStructure(GeneratedYangParser.AppDataStructureContext currentContext) {
+        // do nothing
+    }
+
+    @Override
+    public void enterAppExtendedStatement(GeneratedYangParser.AppExtendedStatementContext currentContext) {
+        AppExtendedNameListener.processAppExtendedNameEntry(this, currentContext);
+    }
+
+    @Override
+    public void exitAppExtendedStatement(GeneratedYangParser.AppExtendedStatementContext currentContext) {
+        // TODO : to be implemented
+    }
+
+    @Override
+    public void enterExtendedName(GeneratedYangParser.ExtendedNameContext currentContext) {
+        // do nothing
+    }
+
+    @Override
+    public void exitExtendedName(GeneratedYangParser.ExtendedNameContext currentContext) {
+        // do nothing
+    }
+
+    @Override
+    public void enterDataStructureKeyStatement(GeneratedYangParser.DataStructureKeyStatementContext ctx) {
+        DataStructureKeyListener.processDataStructureKeyEntry(this, ctx);
+    }
+
+    @Override
+    public void exitDataStructureKeyStatement(GeneratedYangParser.DataStructureKeyStatementContext ctx) {
+        // do nothing
+    }
+
+    @Override
+    public void enterVersion(GeneratedYangParser.VersionContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitVersion(GeneratedYangParser.VersionContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterValue(GeneratedYangParser.ValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitValue(GeneratedYangParser.ValueContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterRequireInstance(GeneratedYangParser.RequireInstanceContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitRequireInstance(GeneratedYangParser.RequireInstanceContext ctx) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterFraction(GeneratedYangParser.FractionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitFraction(GeneratedYangParser.FractionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void visitTerminal(TerminalNode terminalNode) {
+        // do nothing.
+    }
+
+    @Override
+    public void visitErrorNode(ErrorNode errorNode) {
+        // do nothing.
+    }
+
+    @Override
+    public void enterEveryRule(ParserRuleContext parserRuleContext) {
+        // do nothing.
+    }
+
+    @Override
+    public void exitEveryRule(ParserRuleContext parserRuleContext) {
+        // do nothing.
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/YangUtilsParserManager.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/YangUtilsParserManager.java
new file mode 100644
index 0000000..c2b29ed
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/YangUtilsParserManager.java
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl;
+
+import java.io.IOException;
+
+import org.antlr.v4.runtime.ANTLRFileStream;
+import org.antlr.v4.runtime.ANTLRInputStream;
+import org.antlr.v4.runtime.CommonTokenStream;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.antlr.v4.runtime.tree.ParseTreeWalker;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.parser.YangUtilsParser;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangLexer;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.parserutils.ParseTreeErrorListener;
+
+/**
+ * Represents file parsing, parse tree creation and data model tree creation
+ * corresponding to an input YANG file.
+ */
+public class YangUtilsParserManager implements YangUtilsParser {
+
+    @Override
+    public YangNode getDataModel(String yangFile) throws IOException, ParserException {
+
+        /**
+         * Create a char stream that reads from YANG file. Throws an exception
+         * in case input YANG file is either null or non existent.
+         */
+        ANTLRInputStream input;
+        try {
+            input = new ANTLRFileStream(yangFile);
+        } catch (IOException e) {
+            throw new ParserException("YANG file error : YANG file does not exist. " + yangFile);
+        }
+
+        // Create a lexer that feeds off of input char stream.
+        GeneratedYangLexer lexer = new GeneratedYangLexer(input);
+
+        // Create a buffer of tokens pulled from the lexer.
+        CommonTokenStream tokens = new CommonTokenStream(lexer);
+
+        // Create a parser that feeds off the tokens buffer.
+        GeneratedYangParser parser = new GeneratedYangParser(tokens);
+
+        // Remove console error listener.
+        parser.removeErrorListeners();
+
+        // Create instance of customized error listener.
+        ParseTreeErrorListener parseTreeErrorListener = new ParseTreeErrorListener();
+
+        // Add customized error listener to catch errors during parsing.
+        parser.addErrorListener(parseTreeErrorListener);
+
+        ParseTree tree;
+
+        try {
+            // Begin parsing YANG file and generate parse tree.
+            tree = parser.yangfile();
+        } catch (ParserException parserException) {
+            parserException.setFileName(yangFile);
+            throw parserException;
+        }
+
+        // Create a walker to walk the parse tree.
+        ParseTreeWalker walker = new ParseTreeWalker();
+
+        // Create a listener implementation class object.
+        TreeWalkListener treeWalker = new TreeWalkListener();
+        treeWalker.setFileName(yangFile);
+        /**
+         * Walk parse tree, provide call backs to methods in listener and build
+         * data model tree.
+         */
+        try {
+            walker.walk(treeWalker, tree);
+        } catch (ParserException listenerException) {
+            // TODO free incomplete data model tree.
+            listenerException.setFileName(yangFile);
+            throw listenerException;
+        } finally {
+            // TODO free parsable stack
+        }
+
+        // Returns the Root Node of the constructed data model tree.
+        return treeWalker.getRootNode();
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppDataStructureListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppDataStructureListener.java
new file mode 100644
index 0000000..e9ff96c
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppDataStructureListener.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAppDataStructure;
+import org.onosproject.yangutils.datamodel.YangCompilerAnnotation;
+import org.onosproject.yangutils.datamodel.YangDataStructure;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.YangDataStructure.getDataStructureType;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.APP_DATA_STRUCTURE;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidPrefix;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *   app-data-structure-stmt = prefix:app-data-structure-keyword string
+ *                         (";" /
+ *                          "{"
+ *                              [data-structure-key-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ *   appDataStructureStatement : APP_DATA_STRUCTURE appDataStructure (STMTEND | (LEFT_CURLY_BRACE
+ *       dataStructureKeyStatement? RIGHT_CURLY_BRACE));
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "app-data-structure"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class AppDataStructureListener {
+
+    /**
+     * Creates a new app-data-structure listener.
+     */
+    private AppDataStructureListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser receives an
+     * input matching the grammar rule(app-data-structure).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processAppDataStructureEntry(TreeWalkListener listener,
+                                                    GeneratedYangParser.AppDataStructureStatementContext ctx) {
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, APP_DATA_STRUCTURE, "", ENTRY);
+
+        String prefix = getValidPrefix(ctx.APP_DATA_STRUCTURE().getText(), APP_DATA_STRUCTURE, ctx);
+        YangDataStructure dataStructure = getDataStructureType(ctx.appDataStructure().getText());
+
+        YangAppDataStructure appDataStructure = new YangAppDataStructure();
+        appDataStructure.setPrefix(prefix);
+        appDataStructure.setDataStructure(dataStructure);
+        appDataStructure.setLineNumber(ctx.getStart().getLine());
+        appDataStructure.setCharPosition(ctx.getStart().getCharPositionInLine());
+        appDataStructure.setFileName(listener.getFileName());
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangCompilerAnnotation) {
+            YangCompilerAnnotation compilerAnnotation = ((YangCompilerAnnotation) curData);
+            compilerAnnotation.setYangAppDataStructure(appDataStructure);
+            listener.getParsedDataStack().push(appDataStructure);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, APP_DATA_STRUCTURE,
+                    "", ENTRY));
+        }
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser
+     * exits from grammar rule (app-data-structure).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processAppDataStructureExit(TreeWalkListener listener,
+                                                   GeneratedYangParser.AppDataStructureStatementContext ctx) {
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, APP_DATA_STRUCTURE, "", EXIT);
+        if (!(listener.getParsedDataStack().peek() instanceof YangAppDataStructure)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, APP_DATA_STRUCTURE,
+                    "", EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppExtendedNameListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppExtendedNameListener.java
new file mode 100644
index 0000000..7ff8bbe
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AppExtendedNameListener.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAppExtended;
+import org.onosproject.yangutils.datamodel.YangCompilerAnnotation;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.APP_EXTENDED_NAME_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidPrefix;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *   app-extended-stmt = prefix:app-extended-name-keyword string ";"
+ *
+ * ANTLR grammar rule
+ * appExtendedStatement : APP_EXTENDED extendedName STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "app-extended-name"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class AppExtendedNameListener {
+
+    /**
+     * Creates a new app-extended-name listener.
+     */
+    private AppExtendedNameListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser receives an
+     * input matching the grammar rule(app-extended-name).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processAppExtendedNameEntry(TreeWalkListener listener,
+                                                   GeneratedYangParser.AppExtendedStatementContext ctx) {
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, APP_EXTENDED_NAME_DATA, ctx.extendedName().getText(), ENTRY);
+
+        String prefix = getValidPrefix(ctx.APP_EXTENDED().getText(), APP_EXTENDED_NAME_DATA, ctx);
+        YangAppExtended extendedName = new YangAppExtended();
+        extendedName.setPrefix(prefix);
+        extendedName.setYangAppExtendedName(removeQuotesAndHandleConcat(ctx.extendedName().getText()));
+
+        extendedName.setLineNumber(ctx.getStart().getLine());
+        extendedName.setCharPosition(ctx.getStart().getCharPositionInLine());
+        extendedName.setFileName(listener.getFileName());
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangCompilerAnnotation) {
+            YangCompilerAnnotation compilerAnnotation = ((YangCompilerAnnotation) curData);
+            compilerAnnotation.setYangAppExtendedName(extendedName);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, APP_EXTENDED_NAME_DATA,
+                    ctx.extendedName().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java
new file mode 100644
index 0000000..797da12
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java
@@ -0,0 +1,88 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangExtension;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ARGUMENT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * argument-stmt       = argument-keyword sep identifier-arg-str optsep
+ *                       (";" /
+ *                        "{" stmtsep
+ *                            [yin-element-stmt stmtsep]
+ *                        "}")
+ * *
+ * ANTLR grammar rule
+ * argumentStatement : ARGUMENT_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE argumentBody RIGHT_CURLY_BRACE);
+ * argumentBody : yinElementStatement?;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "argument"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ArgumentListener {
+
+    /**
+     * Creates a new argument listener.
+     */
+    private ArgumentListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (argument), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processArgumentEntry(TreeWalkListener listener,
+                                            GeneratedYangParser.ArgumentStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ARGUMENT_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), ARGUMENT_DATA, ctx);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangExtension) {
+            YangExtension extension = ((YangExtension) curData);
+
+            extension.setLineNumber(ctx.getStart().getLine());
+            extension.setCharPosition(ctx.getStart().getCharPositionInLine());
+            extension.setFileName(listener.getFileName());
+            extension.setArgumentName(identifier);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ARGUMENT_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java
new file mode 100644
index 0000000..124f275
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java
@@ -0,0 +1,205 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.util.List;
+
+import org.onosproject.yangutils.datamodel.YangAtomicPath;
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.YangUses;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.AUGMENT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CASE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DATA_DEF_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.WHEN_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidAbsoluteSchemaNodeId;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityEitherOne;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangAugmentNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  augment-stmt        = augment-keyword sep augment-arg-str optsep
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [when-stmt stmtsep]
+ *                            *(if-feature-stmt stmtsep)
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                            1*((data-def-stmt stmtsep) /
+ *                               (case-stmt stmtsep))
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ * augmentStatement : AUGMENT_KEYWORD augment LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | statusStatement
+ *      | descriptionStatement | referenceStatement | dataDefStatement  | caseStatement)* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "augment"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class AugmentListener {
+
+    /**
+     * Creates a new augment listener.
+     */
+    private AugmentListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (augment), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processAugmentEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.AugmentStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, AUGMENT_DATA, ctx.augment().getText(), ENTRY);
+
+        // Validate augment argument string
+        List<YangAtomicPath> targetNodes = getValidAbsoluteSchemaNodeId(ctx.augment().getText(),
+                AUGMENT_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, "", AUGMENT_DATA);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangSubModule) {
+            YangNode curNode = (YangNode) curData;
+            YangAugment yangAugment = getYangAugmentNode(JAVA_GENERATION);
+            yangAugment.setLineNumber(line);
+            yangAugment.setCharPosition(charPositionInLine);
+            yangAugment.setFileName(listener.getFileName());
+            //validateTargetNodePath(targetNodes, curNode, ctx);
+            // TODO: handle in linker.
+
+            yangAugment.setTargetNode(targetNodes);
+            yangAugment.setName(removeQuotesAndHandleConcat(ctx.augment().getText()));
+
+            try {
+                curNode.addChild(yangAugment);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        AUGMENT_DATA, ctx.augment().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(yangAugment);
+
+            // Add resolution information to the list
+            YangResolutionInfoImpl resolutionInfo = new YangResolutionInfoImpl<YangAugment>(yangAugment,
+                    curNode, line,
+                    charPositionInLine);
+            addToResolutionList(resolutionInfo, ctx);
+
+        } else if (curData instanceof YangUses) {
+            throw new ParserException(constructListenerErrorMessage(UNHANDLED_PARSED_DATA, AUGMENT_DATA,
+                    ctx.augment().getText(), ENTRY));
+        }
+        else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, AUGMENT_DATA,
+                    ctx.augment().getText(), ENTRY));
+        }
+
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (augment), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processAugmentExit(TreeWalkListener listener,
+                                          GeneratedYangParser.AugmentStatementContext ctx) {
+
+        //Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, AUGMENT_DATA, ctx.augment().getText(), EXIT);
+
+        if (!(listener.getParsedDataStack().peek() instanceof YangAugment)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, AUGMENT_DATA,
+                    ctx.augment().getText(), EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+
+    /**
+     * Validates the cardinality of augment sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.AugmentStatementContext ctx) {
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, AUGMENT_DATA, ctx.augment().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, AUGMENT_DATA, ctx.augment().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, AUGMENT_DATA, ctx.augment().getText());
+        validateCardinalityMaxOne(ctx.whenStatement(), WHEN_DATA, AUGMENT_DATA, ctx.augment().getText());
+        validateCardinalityEitherOne(ctx.dataDefStatement(), DATA_DEF_DATA, ctx.caseStatement(),
+                CASE_DATA, AUGMENT_DATA, ctx.augment().getText(), ctx);
+    }
+
+    /**
+     * Add to resolution list.
+     *
+     * @param resolutionInfo resolution information.
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangAugment> resolutionInfo,
+                                            GeneratedYangParser.AugmentStatementContext ctx) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    AUGMENT_DATA, ctx.augment().getText(), EXIT, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java
new file mode 100644
index 0000000..8ba4d02
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseFileListener.java
@@ -0,0 +1,93 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.YANGBASE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CHILD;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ANTLR grammar rule
+ * yangfile : module_stmt
+ *          | submodule_stmt;
+ */
+
+/**
+ * Representation of call back function corresponding to the "base rule" defined in
+ * ANTLR grammar file.
+ */
+public final class BaseFileListener {
+
+    /**
+     * Creates a new base listener.
+     */
+    private BaseFileListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (yangfile), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processYangFileEntry(TreeWalkListener listener, GeneratedYangParser.YangfileContext ctx) {
+
+        // Check if stack is empty.
+        checkStackIsEmpty(listener, INVALID_HOLDER, YANGBASE_DATA, "", ENTRY);
+
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (yangfile), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processYangFileExit(TreeWalkListener listener, GeneratedYangParser.YangfileContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, YANGBASE_DATA, "", EXIT);
+
+        // Data Model tree root node is set.
+        if (listener.getParsedDataStack().peek() instanceof YangModule
+                || listener.getParsedDataStack().peek() instanceof YangSubModule) {
+            listener.setRootNode((YangNode) listener.getParsedDataStack().pop());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CHILD, YANGBASE_DATA, "", EXIT));
+        }
+
+        // Check if stack is empty.
+        checkStackIsEmpty(listener, INVALID_HOLDER, YANGBASE_DATA, "", EXIT);
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseListener.java
new file mode 100644
index 0000000..ebf85a7
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BaseListener.java
@@ -0,0 +1,120 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangBase;
+import org.onosproject.yangutils.datamodel.YangIdentity;
+import org.onosproject.yangutils.datamodel.YangIdentityRef;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.*;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNodeIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.BASE_DATA;
+
+/**
+ * base-stmt           = base-keyword sep identifier-ref-arg-str
+ *                          optsep stmtend*
+ * identifier-ref-arg  = [prefix ":"] identifier
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "base"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class BaseListener {
+
+    //Creates a new base listener.
+    private BaseListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree when parser receives an
+     * input matching the grammar rule (base).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBaseEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.BaseStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BASE_DATA, ctx.string().getText(), ENTRY);
+
+        YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(ctx.string().getText(), BASE_DATA, ctx);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+
+        /**
+         * For identityref base node identifier is copied in identity listener itself, so no need to process
+         * base statement for indentityref
+         */
+        if (tmpData instanceof YangIdentityRef) {
+            return;
+        }
+
+        if (!(tmpData instanceof YangIdentity)) {
+             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, BASE_DATA,
+                                                                     ctx.string().getText(), ENTRY));
+        }
+
+        YangBase yangBase = new YangBase();
+        yangBase.setBaseIdentifier(nodeIdentifier);
+        ((YangIdentity) tmpData).setBaseNode(yangBase);
+
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+
+        yangBase.setLineNumber(errorLine);
+        yangBase.setCharPosition(errorPosition);
+        yangBase.setFileName(listener.getFileName());
+
+        // Add resolution information to the list
+        YangResolutionInfoImpl resolutionInfo =
+                new YangResolutionInfoImpl<YangBase>(yangBase, (YangNode) tmpData, errorLine, errorPosition);
+        addToResolutionList(resolutionInfo, ctx);
+    }
+
+    /**
+     * Add to resolution list.
+     *
+     * @param resolutionInfo resolution information
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangBase> resolutionInfo,
+                                            GeneratedYangParser.BaseStatementContext ctx) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    BASE_DATA, ctx.string().getText(), EXIT, e.getMessage()));
+        }
+    }
+
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java
new file mode 100644
index 0000000..4f7ecf8
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BelongsToListener.java
@@ -0,0 +1,142 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangBelongsTo;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.BELONGS_TO_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * submodule-header-stmts =
+ *                            ;; these stmts can appear in any order
+ *                            [yang-version-stmt stmtsep]
+ *                             belongs-to-stmt stmtsep
+ *
+ * belongs-to-stmt     = belongs-to-keyword sep identifier-arg-str
+ *                       optsep
+ *                       "{" stmtsep
+ *                           prefix-stmt stmtsep
+ *                       "}"
+ *
+ * ANTLR grammar rule
+ * submodule_header_statement : yang_version_stmt? belongs_to_stmt
+ *                            | belongs_to_stmt yang_version_stmt?
+ *                            ;
+ * belongs_to_stmt : BELONGS_TO_KEYWORD identifier LEFT_CURLY_BRACE belongs_to_stmt_body RIGHT_CURLY_BRACE;
+ * belongs_to_stmt_body : prefix_stmt;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "belongs to" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class BelongsToListener {
+
+    /**
+     * Creates a new belongto listener.
+     */
+    private BelongsToListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (belongsto), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBelongsToEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.BelongstoStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, ctx.identifier().getText(),
+                ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), BELONGS_TO_DATA, ctx);
+
+        YangBelongsTo belongstoNode = new YangBelongsTo();
+        belongstoNode.setBelongsToModuleName(identifier);
+
+        // Set the line number and character position in line for the belongs to.
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+        belongstoNode.setLineNumber(errorLine);
+        belongstoNode.setCharPosition(errorPosition);
+        belongstoNode.setFileName(listener.getFileName());
+
+        // Push belongsto into the stack.
+        listener.getParsedDataStack().push(belongstoNode);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (belongsto), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBelongsToExit(TreeWalkListener listener,
+                                            GeneratedYangParser.BelongstoStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA, ctx.identifier().getText(),
+                EXIT);
+
+        Parsable tmpBelongstoNode = listener.getParsedDataStack().peek();
+        if (tmpBelongstoNode instanceof YangBelongsTo) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, BELONGS_TO_DATA,
+                    ctx.identifier().getText(), EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case SUB_MODULE_DATA: {
+                    YangSubModule subModule = (YangSubModule) tmpNode;
+                    subModule.setBelongsTo((YangBelongsTo) tmpBelongstoNode);
+                    subModule.setPrefix(subModule.getBelongsTo().getPrefix());
+                    break;
+                }
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, BELONGS_TO_DATA,
+                            ctx.identifier().getText(),
+                            EXIT));
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, BELONGS_TO_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitListener.java
new file mode 100644
index 0000000..bd60910
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitListener.java
@@ -0,0 +1,182 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * bit-stmt            = bit-keyword sep identifier-arg-str optsep
+ *                       (";" /
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [position-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                          "}"
+ *                        "}")
+ *
+ * ANTLR grammar rule
+ * bitStatement : BIT_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE bitBodyStatement RIGHT_CURLY_BRACE);
+ *
+ * bitBodyStatement : positionStatement? statusStatement? descriptionStatement? referenceStatement?
+ *               | positionStatement? statusStatement? referenceStatement? descriptionStatement?
+ *               | positionStatement? descriptionStatement? statusStatement? referenceStatement?
+ *               | positionStatement? descriptionStatement? referenceStatement? statusStatement?
+ *               | positionStatement? referenceStatement? statusStatement? descriptionStatement?
+ *               | positionStatement? referenceStatement? descriptionStatement? statusStatement?
+ *               | statusStatement? positionStatement? descriptionStatement? referenceStatement?
+ *               | statusStatement? positionStatement? referenceStatement? descriptionStatement?
+ *               | statusStatement? descriptionStatement? descriptionStatement? positionStatement?
+ *               | statusStatement? descriptionStatement? positionStatement? descriptionStatement?
+ *               | statusStatement? referenceStatement? positionStatement? descriptionStatement?
+ *               | statusStatement? referenceStatement? descriptionStatement? positionStatement?
+ *               | descriptionStatement? positionStatement? statusStatement? referenceStatement?
+ *               | descriptionStatement? positionStatement? referenceStatement? statusStatement?
+ *               | descriptionStatement? statusStatement? positionStatement? referenceStatement?
+ *               | descriptionStatement? statusStatement? referenceStatement? positionStatement?
+ *               | descriptionStatement? referenceStatement? positionStatement? statusStatement?
+ *               | descriptionStatement? referenceStatement? statusStatement? positionStatement?
+ *               | referenceStatement? positionStatement? descriptionStatement? statusStatement?
+ *               | referenceStatement? positionStatement? statusStatement? descriptionStatement?
+ *               | referenceStatement? statusStatement? descriptionStatement? positionStatement?
+ *               | referenceStatement? statusStatement? positionStatement? descriptionStatement?
+ *               | referenceStatement? descriptionStatement? positionStatement? statusStatement?
+ *               | referenceStatement? descriptionStatement? statusStatement? positionStatement?
+ *               ;
+ */
+
+import java.util.Map;
+
+import org.onosproject.yangutils.datamodel.YangBit;
+import org.onosproject.yangutils.datamodel.YangBits;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.BIT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CONTENT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "bit"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class BitListener {
+
+    /**
+     * Creates a new bit listener.
+     */
+    private BitListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (bit), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBitEntry(TreeWalkListener listener,
+                                       GeneratedYangParser.BitStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BIT_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), BIT_DATA, ctx);
+
+        YangBit bitNode = new YangBit();
+        bitNode.setBitName(identifier);
+
+        bitNode.setLineNumber(ctx.getStart().getLine());
+        bitNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+        bitNode.setFileName(listener.getFileName());
+        listener.getParsedDataStack().push(bitNode);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (bit), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBitExit(TreeWalkListener listener,
+                                      GeneratedYangParser.BitStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BIT_DATA, ctx.identifier().getText(), EXIT);
+
+        Parsable tmpBitNode = listener.getParsedDataStack().peek();
+        if (tmpBitNode instanceof YangBit) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, BIT_DATA, ctx.identifier().getText(), EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case BITS_DATA: {
+                    YangBits yangBits = (YangBits) tmpNode;
+                    if (ctx.bitBodyStatement() == null || ctx.bitBodyStatement().positionStatement() == null) {
+                        int maxPosition = 0;
+                        boolean isPositionPresent = false;
+
+                        for (Map.Entry<Integer, YangBit> element : yangBits.getBitPositionMap().entrySet()) {
+                            if (maxPosition <= element.getKey()) {
+                                maxPosition = element.getKey();
+                                isPositionPresent = true;
+                            }
+                        }
+
+                        if (isPositionPresent) {
+                            maxPosition++;
+                        }
+                        ((YangBit) tmpBitNode).setPosition(maxPosition);
+                    }
+                    try {
+                        yangBits.addBitInfo((YangBit) tmpBitNode);
+                    } catch (DataModelException e) {
+                        ParserException parserException = new ParserException(constructExtendedListenerErrorMessage(
+                                INVALID_CONTENT, BIT_DATA, ctx.identifier().getText(), EXIT, e.getMessage()));
+                        parserException.setLine(ctx.getStart().getLine());
+                        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                        throw parserException;
+                    }
+                    break;
+                }
+                default:
+                    throw new ParserException(
+                            constructListenerErrorMessage(INVALID_HOLDER, BIT_DATA, ctx.identifier().getText(), EXIT));
+            }
+        } else {
+            throw new ParserException(
+                    constructListenerErrorMessage(MISSING_CURRENT_HOLDER, BIT_DATA, ctx.identifier().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java
new file mode 100644
index 0000000..a476902
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/BitsListener.java
@@ -0,0 +1,165 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * type-body-stmts     = numerical-restrictions /
+ *                       decimal64-specification /
+ *                      string-restrictions /
+ *                       enum-specification /
+ *                       leafref-specification /
+ *                       identityref-specification /
+ *                       instance-identifier-specification /
+ *                       bits-specification /
+ *                       union-specification
+ *
+ * bits-specification  = 1*(bit-stmt stmtsep)
+ *
+ * ANTLR grammar rule
+ *
+ * typeBodyStatements : numericalRestrictions | stringRestrictions | enumSpecification
+ *                 | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+ *                 | bitsSpecification | unionSpecification;
+ *
+ * bitsSpecification : bitStatement+;
+ */
+
+import org.onosproject.yangutils.datamodel.YangBits;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.YangUnion;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.BITS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "bits" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class BitsListener {
+
+    /**
+     * Creates a new bits listener.
+     */
+    private BitsListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (bits), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBitsEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.BitsSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BITS_DATA, "", ENTRY);
+
+        if (listener.getParsedDataStack().peek() instanceof YangType) {
+            YangBits bitsNode = new YangBits();
+
+            bitsNode.setLineNumber(ctx.getStart().getLine());
+            bitsNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+            bitsNode.setFileName(listener.getFileName());
+            Parsable typeData = listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, BITS_DATA, "", ENTRY);
+
+            Parsable tmpData = listener.getParsedDataStack().peek();
+
+            switch (tmpData.getYangConstructType()) {
+                case LEAF_DATA:
+                    bitsNode.setBitsName(((YangLeaf) tmpData).getName());
+                    break;
+                case LEAF_LIST_DATA:
+                    bitsNode.setBitsName(((YangLeafList) tmpData).getName());
+                    break;
+                case TYPEDEF_DATA:
+                    bitsNode.setBitsName(((YangTypeDef) tmpData).getName());
+                    break;
+                case UNION_DATA:
+                    bitsNode.setBitsName(((YangUnion) tmpData).getName());
+                    break;
+                // TODO typedef, union, deviate.
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                            ((YangType<?>) typeData).getDataTypeName(), ENTRY));
+            }
+            listener.getParsedDataStack().push(typeData);
+            listener.getParsedDataStack().push(bitsNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, BITS_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (bits), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processBitsExit(TreeWalkListener listener,
+                                       GeneratedYangParser.BitsSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, BITS_DATA, "", EXIT);
+
+        Parsable tmpBitsNode = listener.getParsedDataStack().peek();
+        if (tmpBitsNode instanceof YangBits) {
+            YangBits bitsNode = (YangBits) tmpBitsNode;
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, BITS_DATA, "", EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case TYPE_DATA: {
+                    YangType<YangBits> typeNode = (YangType<YangBits>) tmpNode;
+                    typeNode.setDataTypeExtendedInfo(bitsNode);
+                    break;
+                }
+                default:
+                    throw new ParserException(
+                            constructListenerErrorMessage(INVALID_HOLDER, BITS_DATA, "", EXIT));
+            }
+        } else {
+            throw new ParserException(
+                    constructListenerErrorMessage(MISSING_CURRENT_HOLDER, BITS_DATA, "", EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java
new file mode 100644
index 0000000..f3803da
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java
@@ -0,0 +1,161 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangChoice;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CASE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.WHEN_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangCaseNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  case-stmt           = case-keyword sep identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [when-stmt stmtsep]
+ *                             *(if-feature-stmt stmtsep)
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                             *(data-def-stmt stmtsep)
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ * caseStatement : CASE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement
+ *               | statusStatement | descriptionStatement | referenceStatement | dataDefStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "case" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class CaseListener {
+
+    /**
+     * Create a new case listener.
+     */
+    private CaseListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (case), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processCaseEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.CaseStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CASE_DATA, ctx.identifier().getText(), ENTRY);
+
+        // Check validity of identifier and remove double quotes.
+        String identifier = getValidIdentifier(ctx.identifier().getText(), CASE_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, CASE_DATA);
+
+        if (curData instanceof YangChoice || curData instanceof YangAugment) {
+            YangCase caseNode = getYangCaseNode(JAVA_GENERATION);
+            caseNode.setName(identifier);
+            caseNode.setLineNumber(line);
+            caseNode.setCharPosition(charPositionInLine);
+            caseNode.setFileName(listener.getFileName());
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(caseNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        CASE_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(caseNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, CASE_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (case), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processCaseExit(TreeWalkListener listener,
+                                       GeneratedYangParser.CaseStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CASE_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangCase) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, CASE_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of case sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.CaseStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.whenStatement(), WHEN_DATA, CASE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, CASE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, CASE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, CASE_DATA, ctx.identifier().getText());
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java
new file mode 100644
index 0000000..00b9973
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java
@@ -0,0 +1,202 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangChoice;
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CHOICE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DEFAULT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MANDATORY_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.WHEN_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CONTENT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangChoiceNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  choice-stmt         = choice-keyword sep identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [when-stmt stmtsep]
+ *                             *(if-feature-stmt stmtsep)
+ *                             [default-stmt stmtsep]
+ *                             [config-stmt stmtsep]
+ *                             [mandatory-stmt stmtsep]
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                             *((short-case-stmt / case-stmt) stmtsep)
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ * choiceStatement : CHOICE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement
+ *                 | defaultStatement | configStatement | mandatoryStatement | statusStatement | descriptionStatement
+ *                 | referenceStatement | shortCaseStatement | caseStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "choice"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ChoiceListener {
+
+    /**
+     * Create a new choice listener.
+     */
+    private ChoiceListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (choice), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processChoiceEntry(TreeWalkListener listener,
+                                          GeneratedYangParser.ChoiceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CHOICE_DATA, ctx.identifier().getText(), ENTRY);
+
+        // Check validity of identifier and remove double quotes.
+        String identifier = getValidIdentifier(ctx.identifier().getText(), CHOICE_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, CHOICE_DATA);
+
+        if (curData instanceof YangModule || curData instanceof YangSubModule || curData instanceof YangContainer
+                || curData instanceof YangList || curData instanceof YangCase || curData instanceof YangGrouping
+                || curData instanceof YangAugment || curData instanceof YangInput || curData instanceof YangOutput
+                || curData instanceof YangNotification) {
+
+            YangChoice choiceNode = getYangChoiceNode(JAVA_GENERATION);
+            choiceNode.setName(identifier);
+            choiceNode.setLineNumber(line);
+            choiceNode.setCharPosition(charPositionInLine);
+            choiceNode.setFileName(listener.getFileName());
+            /*
+             * If "config" is not specified, the default is the same as the parent
+             * schema node's "config" value.
+             */
+            if (ctx.configStatement().isEmpty()) {
+                boolean parentConfig = ListenerValidation.getParentNodeConfig(listener);
+                choiceNode.setConfig(parentConfig);
+            }
+
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(choiceNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        CHOICE_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(choiceNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    CHOICE_DATA, ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (choice), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processChoiceExit(TreeWalkListener listener,
+            GeneratedYangParser.ChoiceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CHOICE_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangChoice) {
+            YangChoice choiceNode = (YangChoice) listener.getParsedDataStack().peek();
+            try {
+                choiceNode.validateDataOnExit();
+            } catch (DataModelException e) {
+                throw new ParserException(constructListenerErrorMessage(INVALID_CONTENT, CHOICE_DATA,
+                                                                        ctx.identifier().getText(), EXIT));
+            }
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, CHOICE_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of choice sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule.
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.ChoiceStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.whenStatement(), WHEN_DATA, CHOICE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.defaultStatement(), DEFAULT_DATA, CHOICE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.configStatement(), CONFIG_DATA, CHOICE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.mandatoryStatement(), MANDATORY_DATA, CHOICE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, CHOICE_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, CHOICE_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, CHOICE_DATA, ctx.identifier().getText());
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CompilerAnnotationListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CompilerAnnotationListener.java
new file mode 100644
index 0000000..ed892b3
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CompilerAnnotationListener.java
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.util.List;
+
+import org.onosproject.yangutils.datamodel.YangAtomicPath;
+import org.onosproject.yangutils.datamodel.YangCompilerAnnotation;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.COMPILER_ANNOTATION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidAbsoluteSchemaNodeId;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidPrefix;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *   compiler-annotation-stmt = prefix:compiler-annotation-keyword string
+ *                          "{"
+ *                              [app-data-structure-stmt stmtsep]
+ *                              [app-extended-stmt stmtsep]
+ *                          "}"
+ *
+ * ANTLR grammar rule
+ *   compilerAnnotationStatement : COMPILER_ANNOTATION string LEFT_CURLY_BRACE
+ *        compilerAnnotationBodyStatement RIGHT_CURLY_BRACE;
+ *
+ *   compilerAnnotationBodyStatement : appDataStructureStatement? appExtendedStatement? ;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "compiler-annotation"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class CompilerAnnotationListener {
+
+    /**
+     * Creates a new compiler-annotation listener.
+     */
+    private CompilerAnnotationListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser receives an
+     * input matching the grammar rule(compiler-annotation).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processCompilerAnnotationEntry(TreeWalkListener listener,
+                                                      GeneratedYangParser.CompilerAnnotationStatementContext ctx) {
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, COMPILER_ANNOTATION_DATA, ctx.string().getText(), ENTRY);
+        String prefix = getValidPrefix(ctx.COMPILER_ANNOTATION().getText(), COMPILER_ANNOTATION_DATA, ctx);
+
+        YangCompilerAnnotation compilerAnnotation = new YangCompilerAnnotation();
+        compilerAnnotation.setPrefix(prefix);
+        compilerAnnotation.setPath(removeQuotesAndHandleConcat(ctx.string().getText()));
+
+        compilerAnnotation.setLineNumber(ctx.getStart().getLine());
+        compilerAnnotation.setCharPosition(ctx.getStart().getCharPositionInLine());
+        compilerAnnotation.setFileName(listener.getFileName());
+        // Validate augment argument string
+        List<YangAtomicPath> targetNodes = getValidAbsoluteSchemaNodeId(ctx.string().getText(),
+                                                                        COMPILER_ANNOTATION_DATA, ctx);
+
+        compilerAnnotation.setAtomicPathList(targetNodes);
+
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (!(curData instanceof YangModule || curData instanceof YangSubModule)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, COMPILER_ANNOTATION_DATA,
+                                                                    ctx.string().getText(), ENTRY));
+        }
+
+        // Add resolution information to the list
+        YangResolutionInfoImpl resolutionInfo = new YangResolutionInfoImpl<YangCompilerAnnotation>(
+                compilerAnnotation, (YangNode) curData, line, charPositionInLine);
+        addToResolutionList(resolutionInfo, ctx);
+
+        listener.getParsedDataStack().push(compilerAnnotation);
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser
+     * exits from grammar rule (compiler-annotation).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processCompilerAnnotationExit(TreeWalkListener listener,
+                                                     GeneratedYangParser.CompilerAnnotationStatementContext ctx) {
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, COMPILER_ANNOTATION_DATA, ctx.string().getText(), EXIT);
+        if (!(listener.getParsedDataStack().peek() instanceof YangCompilerAnnotation)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, COMPILER_ANNOTATION_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+
+    /**
+     * Adds to resolution list.
+     *
+     * @param resolutionInfo resolution information.
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangCompilerAnnotation> resolutionInfo,
+                                            GeneratedYangParser.CompilerAnnotationStatementContext ctx) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    COMPILER_ANNOTATION_DATA, ctx.COMPILER_ANNOTATION().getText(), ENTRY, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java
new file mode 100644
index 0000000..d595cb0
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidBooleanValue;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * config-stmt         = config-keyword sep
+ *                       config-arg-str stmtend
+ * config-arg-str      = < a string that matches the rule
+ *                         config-arg >
+ * config-arg          = true-keyword / false-keyword
+ *
+ * ANTLR grammar rule
+ * configStatement : CONFIG_KEYWORD config STMTEND;
+ * config          : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "config"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ConfigListener {
+
+    /**
+     * Creates a new config listener.
+     */
+    private ConfigListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (config), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processConfigEntry(TreeWalkListener listener,
+            GeneratedYangParser.ConfigStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONFIG_DATA, "", ENTRY);
+
+        boolean isConfig = getValidBooleanValue(ctx.config().getText(), CONFIG_DATA, ctx);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_DATA:
+                YangLeaf leaf = (YangLeaf) tmpData;
+                leaf.setConfig(isConfig);
+                break;
+            case CONTAINER_DATA:
+                YangContainer container = (YangContainer) tmpData;
+                container.setConfig(isConfig);
+                break;
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setConfig(isConfig);
+                break;
+            case LIST_DATA:
+                YangList yangList = (YangList) tmpData;
+                yangList.setConfig(isConfig);
+                break;
+            case CHOICE_DATA: // TODO
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, CONFIG_DATA, "", ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java
new file mode 100644
index 0000000..4cab95d
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContactListener.java
@@ -0,0 +1,115 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONTACT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * meta-stmts          = ;; these stmts can appear in any order
+ *                       [organization-stmt stmtsep]
+ *                       [contact-stmt stmtsep]
+ *                       [description-stmt stmtsep]
+ *                       [reference-stmt stmtsep]
+ * contact-stmt        = contact-keyword sep string optsep stmtend
+ *
+ * ANTLR grammar rule
+ * meta_stmts : organization_stmt? contact_stmt? description_stmt? reference_stmt?
+ *            | organization_stmt? contact_stmt? reference_stmt? description_stmt?
+ *            | organization_stmt? description_stmt? contact_stmt? reference_stmt?
+ *            | organization_stmt? description_stmt? reference_stmt? contact_stmt?
+ *            | organization_stmt? reference_stmt? contact_stmt? description_stmt?
+ *            | organization_stmt? reference_stmt? description_stmt? contact_stmt?
+ *            | contact_stmt? organization_stmt? description_stmt? reference_stmt?
+ *            | contact_stmt? organization_stmt? reference_stmt? description_stmt?
+ *            | contact_stmt? reference_stmt? organization_stmt? description_stmt?
+ *            | contact_stmt? reference_stmt? description_stmt? organization_stmt?
+ *            | contact_stmt? description_stmt? reference_stmt? organization_stmt?
+ *            | contact_stmt? description_stmt? organization_stmt? reference_stmt?
+ *            | reference_stmt? contact_stmt? organization_stmt? description_stmt?
+ *            | reference_stmt? contact_stmt? description_stmt? organization_stmt?
+ *            | reference_stmt? organization_stmt? contact_stmt? description_stmt?
+ *            | reference_stmt? organization_stmt? description_stmt? contact_stmt?
+ *            | reference_stmt? description_stmt? organization_stmt? contact_stmt?
+ *            | reference_stmt? description_stmt? contact_stmt? organization_stmt?
+ *            | description_stmt? reference_stmt? contact_stmt? organization_stmt?
+ *            | description_stmt? reference_stmt? organization_stmt? contact_stmt?
+ *            | description_stmt? contact_stmt? reference_stmt? organization_stmt?
+ *            | description_stmt? contact_stmt? organization_stmt? reference_stmt?
+ *            | description_stmt? organization_stmt? contact_stmt? reference_stmt?
+ *            | description_stmt? organization_stmt? reference_stmt? contact_stmt?
+ *            ;
+ * contact_stmt : CONTACT_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "contact"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ContactListener {
+
+    /**
+     * Creates a new contact listener.
+     */
+    private ContactListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (contact), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processContactEntry(TreeWalkListener listener, GeneratedYangParser.ContactStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONTACT_DATA, ctx.string().getText(), ENTRY);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case MODULE_DATA: {
+                YangModule module = (YangModule) tmpNode;
+                module.setContact(ctx.string().getText());
+                break;
+            }
+            case SUB_MODULE_DATA: {
+                YangSubModule subModule = (YangSubModule) tmpNode;
+                subModule.setContact(ctx.string().getText());
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, CONTACT_DATA,
+                        ctx.string().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java
new file mode 100644
index 0000000..7ea261b
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java
@@ -0,0 +1,205 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONTAINER_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.PRESENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangContainerNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  container-stmt      = container-keyword sep identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [when-stmt stmtsep]
+ *                             *(if-feature-stmt stmtsep)
+ *                             *(must-stmt stmtsep)
+ *                             [presence-stmt stmtsep]
+ *                             [config-stmt stmtsep]
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                             *((typedef-stmt /
+ *                                grouping-stmt) stmtsep)
+ *                             *(data-def-stmt stmtsep)
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ *  containerStatement : CONTAINER_KEYWORD identifier
+ *                   (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | mustStatement |
+ *                   presenceStatement | configStatement | statusStatement | descriptionStatement |
+ *                   referenceStatement | typedefStatement | groupingStatement
+ *                    | dataDefStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "container"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ContainerListener {
+
+    /**
+     * Creates a new container listener.
+     */
+    private ContainerListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (container), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processContainerEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.ContainerStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONTAINER_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), CONTAINER_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, CONTAINER_DATA);
+
+        YangContainer container = getYangContainerNode(JAVA_GENERATION);
+        container.setName(identifier);
+
+        container.setLineNumber(line);
+        container.setCharPosition(charPositionInLine);
+        container.setFileName(listener.getFileName());
+        /*
+         * If "config" is not specified, the default is the same as the parent
+         * schema node's "config" value.
+         */
+        if (ctx.configStatement().isEmpty()) {
+            boolean parentConfig = ListenerValidation.getParentNodeConfig(listener);
+            container.setConfig(parentConfig);
+        }
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangSubModule
+                || curData instanceof YangContainer || curData instanceof YangList
+                || curData instanceof YangCase || curData instanceof YangNotification
+                || curData instanceof YangInput || curData instanceof YangOutput
+                || curData instanceof YangAugment || curData instanceof YangGrouping) {
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(container);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        CONTAINER_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(container);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, CONTAINER_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (container), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processContainerExit(TreeWalkListener listener,
+                                            GeneratedYangParser.ContainerStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, CONTAINER_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangContainer) {
+            YangContainer yangContainer = (YangContainer) listener.getParsedDataStack().peek();
+            try {
+                yangContainer.validateDataOnExit();
+            } catch (DataModelException e) {
+                ParserException parserException = new ParserException(constructExtendedListenerErrorMessage(
+                        UNHANDLED_PARSED_DATA, CONTAINER_DATA, ctx.identifier().getText(), EXIT, e.getMessage()));
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, CONTAINER_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of container sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.ContainerStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.presenceStatement(), PRESENCE_DATA, CONTAINER_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.configStatement(), CONFIG_DATA, CONTAINER_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, CONTAINER_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, CONTAINER_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, CONTAINER_DATA, ctx.identifier().getText());
+        // TODO validate 'when' cardinality
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DataStructureKeyListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DataStructureKeyListener.java
new file mode 100644
index 0000000..9cee91f
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DataStructureKeyListener.java
@@ -0,0 +1,91 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAppDataStructure;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.KEY_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.utils.UtilConstants.SPACE;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *   data-structure-key-stmt = prefix:key-keyword string ";"
+ *
+ * ANTLR grammar rule
+ *   dataStructureKeyStatement : DATA_STRUCTURE_KEY string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "key"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class DataStructureKeyListener {
+
+    /**
+     * Creates a new data-structure-key listener.
+     */
+    private DataStructureKeyListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser receives an
+     * input matching the grammar rule(key).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processDataStructureKeyEntry(TreeWalkListener listener,
+                                                    GeneratedYangParser.DataStructureKeyStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, KEY_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (listener.getParsedDataStack().peek() instanceof YangAppDataStructure) {
+            YangAppDataStructure dataStructure = (YangAppDataStructure) tmpData;
+
+            dataStructure.setLineNumber(ctx.getStart().getLine());
+            dataStructure.setCharPosition(ctx.getStart().getCharPositionInLine());
+            dataStructure.setFileName(listener.getFileName());
+            String tmpKeyValue = removeQuotesAndHandleConcat(ctx.string().getText());
+            if (tmpKeyValue.contains(SPACE)) {
+                String[] keyValues = tmpKeyValue.split(SPACE);
+                for (String keyValue : keyValues) {
+                    dataStructure.addKey(keyValue);
+                }
+            } else {
+                dataStructure.addKey(tmpKeyValue);
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, KEY_DATA, ctx.string().getText(),
+                    ENTRY));
+        }
+    }
+}
+
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/Decimal64Listener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/Decimal64Listener.java
new file mode 100644
index 0000000..14ae935
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/Decimal64Listener.java
@@ -0,0 +1,151 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * type-body-stmts     = numerical-restrictions /
+ *                       decimal64-specification /
+ *                       string-restrictions /
+ *                       enum-specification /
+ *                       leafref-specification /
+ *                       identityref-specification /
+ *                       instance-identifier-specification /
+ *                       bits-specification /
+ *                       union-specification
+ *
+ * decimal64-specification = fraction-digits-stmt [range-stmt stmtsep]
+ *
+ * fraction-digits-stmt = fraction-digits-keyword sep
+ *                         fraction-digits-arg-str stmtend
+ *
+ * fraction-digits-arg-str = < a string that matches the rule
+ *                             fraction-digits-arg >
+ *
+ * fraction-digits-arg = ("1" ["0" / "1" / "2" / "3" / "4" /
+ *                              "5" / "6" / "7" / "8"])
+ *                        / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
+ *
+ * range-stmt          = range-keyword sep range-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [error-message-stmt stmtsep]
+ *                             [error-app-tag-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ * ANTLR grammar rule
+ *
+ * typeBodyStatements : numericalRestrictions | decimal64Specification | stringRestrictions | enumSpecification
+ *                     | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+ *                     | bitsSpecification | unionSpecification;
+ *
+ * decimal64Specification : fractionDigitStatement rangeStatement?;
+ *
+ * fractionDigitStatement : FRACTION_DIGITS_KEYWORD fraction STMTEND;
+ *
+ * fraction : string;
+ */
+
+import org.onosproject.yangutils.datamodel.YangDecimal64;
+import org.onosproject.yangutils.datamodel.YangRangeRestriction;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DECIMAL64_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "decimal64" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class Decimal64Listener {
+
+    /**
+     * Creates a new Decimal64 listener.
+     */
+    private Decimal64Listener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (decimal64), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processDecimal64Entry(TreeWalkListener listener,
+                                             GeneratedYangParser.Decimal64SpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, DECIMAL64_DATA, "", ENTRY);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangType) {
+            YangType<YangDecimal64<YangRangeRestriction>> typeNode =
+                    (YangType<YangDecimal64<YangRangeRestriction>>) tmpNode;
+            YangDecimal64 decimal64Node = new YangDecimal64();
+            typeNode.setDataTypeExtendedInfo(decimal64Node);
+
+            decimal64Node.setLineNumber(ctx.getStart().getLine());
+            decimal64Node.setCharPosition(ctx.getStart().getCharPositionInLine());
+            decimal64Node.setFileName(listener.getFileName());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, DECIMAL64_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * Performs validation and updates the data model tree.
+     * It is called when parser exits from grammar rule (decimal64).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processDecimal64Exit(TreeWalkListener listener,
+                                            GeneratedYangParser.Decimal64SpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, DECIMAL64_DATA, "", EXIT);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangType) {
+            YangType<YangDecimal64<YangRangeRestriction>> typeNode =
+                    (YangType<YangDecimal64<YangRangeRestriction>>) tmpNode;
+            YangDecimal64<YangRangeRestriction> decimal64Node = typeNode.getDataTypeExtendedInfo();
+            try {
+                decimal64Node.validateRange();
+            } catch (DataModelException e) {
+                throw new ParserException(e);
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, DECIMAL64_DATA, "", EXIT));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java
new file mode 100644
index 0000000..b93fe52
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DefaultListener.java
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           ;; these stmts can appear in any order
+ *                           type-stmt stmtsep
+ *                          [units-stmt stmtsep]
+ *                           [default-stmt stmtsep]
+ *                           [status-stmt stmtsep]
+ *                           [description-stmt stmtsep]
+ *                           [reference-stmt stmtsep]
+ *                         "}"
+ * default-stmt        = default-keyword sep string stmtend
+
+ *
+ * ANTLR grammar rule
+ * typedefStatement : TYPEDEF_KEYWORD IDENTIFIER LEFT_CURLY_BRACE
+ *                (typeStatement | unitsStatement | defaultStatement | statusStatement
+ *                | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ * defaultStatement : DEFAULT_KEYWORD string STMTEND;
+ */
+
+import org.onosproject.yangutils.datamodel.YangChoice;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DEFAULT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener for default YANG statement.
+ */
+public final class DefaultListener {
+
+    /**
+     * Creates a new default listener.
+     */
+    private DefaultListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (default), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processDefaultEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.DefaultStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, DEFAULT_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case TYPEDEF_DATA: {
+                YangTypeDef typeDef = (YangTypeDef) tmpNode;
+                typeDef.setDefaultValueInString(removeQuotesAndHandleConcat(ctx.string().getText()));
+                break;
+            }
+            case LEAF_DATA: {
+                YangLeaf leaf = (YangLeaf) tmpNode;
+                leaf.setDefaultValueInString(removeQuotesAndHandleConcat(ctx.string().getText()));
+                break;
+            }
+            case CHOICE_DATA: {
+                YangChoice choice = (YangChoice) tmpNode;
+                choice.setDefaultValueInString(removeQuotesAndHandleConcat(ctx.string().getText()));
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                        DEFAULT_DATA, ctx.string().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DescriptionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DescriptionListener.java
new file mode 100644
index 0000000..c7988a8
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/DescriptionListener.java
@@ -0,0 +1,77 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangDesc;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * description-stmt    = description-keyword sep string optsep stmtend
+ *
+ * ANTLR grammar rule
+ * descriptionStatement : DESCRIPTION_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "description" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class DescriptionListener {
+
+    /**
+     * Creates a new description listener.
+     */
+    private DescriptionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (description), perform validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processDescriptionEntry(TreeWalkListener listener,
+            GeneratedYangParser.DescriptionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, DESCRIPTION_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangDesc) {
+            YangDesc description = (YangDesc) tmpData;
+            description.setDescription(ctx.string().getText());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, DESCRIPTION_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumListener.java
new file mode 100644
index 0000000..b0beef5
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumListener.java
@@ -0,0 +1,190 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  enum-stmt           = enum-keyword sep string optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [value-stmt stmtsep]
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ * enumStatement : ENUM_KEYWORD string (STMTEND | LEFT_CURLY_BRACE enumStatementBody RIGHT_CURLY_BRACE);
+ *
+ *         enumStatementBody : valueStatement? statusStatement? descriptionStatement? referenceStatement?
+ *         | valueStatement? statusStatement? referenceStatement? descriptionStatement?
+ *         | valueStatement? descriptionStatement? statusStatement? referenceStatement?
+ *         | valueStatement? descriptionStatement? referenceStatement? statusStatement?
+ *         | valueStatement? referenceStatement? statusStatement? descriptionStatement?
+ *         | valueStatement? referenceStatement? descriptionStatement? statusStatement?
+ *         | statusStatement? valueStatement? descriptionStatement? referenceStatement?
+ *         | statusStatement? valueStatement? referenceStatement? descriptionStatement?
+ *         | statusStatement? descriptionStatement? descriptionStatement? valueStatement?
+ *         | statusStatement? descriptionStatement? valueStatement? descriptionStatement?
+ *         | statusStatement? referenceStatement? valueStatement? descriptionStatement?
+ *         | statusStatement? referenceStatement? descriptionStatement? valueStatement?
+ *         | descriptionStatement? valueStatement? statusStatement? referenceStatement?
+ *         | descriptionStatement? valueStatement? referenceStatement? statusStatement?
+ *         | descriptionStatement? statusStatement? valueStatement? referenceStatement?
+ *         | descriptionStatement? statusStatement? referenceStatement? valueStatement?
+ *         | descriptionStatement? referenceStatement? valueStatement? statusStatement?
+ *         | descriptionStatement? referenceStatement? statusStatement? valueStatement?
+ *         | referenceStatement? valueStatement? descriptionStatement? statusStatement?
+ *         | referenceStatement? valueStatement? statusStatement? descriptionStatement?
+ *         | referenceStatement? statusStatement? descriptionStatement? valueStatement?
+ *         | referenceStatement? statusStatement? valueStatement? descriptionStatement?
+ *         | referenceStatement? descriptionStatement? valueStatement? statusStatement?
+ *         | referenceStatement? descriptionStatement? statusStatement? valueStatement?
+ *         ;
+ */
+
+import org.onosproject.yangutils.datamodel.YangEnum;
+import org.onosproject.yangutils.datamodel.YangEnumeration;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ENUM_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.DUPLICATE_ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.utils.UtilConstants.QUOTES;
+import static org.onosproject.yangutils.utils.UtilConstants.EMPTY_STRING;
+
+/**
+ * Represents listener based call back function corresponding to the "enum" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class EnumListener {
+
+    /**
+     * Creates a new enum listener.
+     */
+    private EnumListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (enum), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processEnumEntry(TreeWalkListener listener, GeneratedYangParser.EnumStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUM_DATA, ctx.string().getText(), ENTRY);
+
+        YangEnum enumNode = new YangEnum();
+        enumNode.setNamedValue(getValidNamedValue(ctx.string().getText()));
+
+        enumNode.setLineNumber(ctx.getStart().getLine());
+        enumNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+        enumNode.setFileName(listener.getFileName());
+        listener.getParsedDataStack().push(enumNode);
+    }
+
+    /*Removes quotes from the enum name if present.*/
+    private static String getValidNamedValue(String name) {
+        if (name.contains(QUOTES)) {
+            name = name.replace(QUOTES, EMPTY_STRING);
+        }
+        return name;
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (enum), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processEnumExit(TreeWalkListener listener, GeneratedYangParser.EnumStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUM_DATA, ctx.string().getText(), EXIT);
+
+        Parsable tmpEnumNode = listener.getParsedDataStack().peek();
+        if (tmpEnumNode instanceof YangEnum) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUM_DATA, ctx.string().getText(), EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case ENUMERATION_DATA: {
+                    YangEnumeration yangEnumeration = (YangEnumeration) tmpNode;
+                    if (ctx.enumStatementBody() == null || ctx.enumStatementBody().valueStatement() == null) {
+                        int maxValue = 0;
+                        boolean isValuePresent = false;
+
+                        for (YangEnum curEnum : yangEnumeration.getEnumSet()) {
+                            if (curEnum.getValue() == Integer.MAX_VALUE) {
+                                ParserException parserException = new ParserException("YANG file error : "
+                                        + "An enum value MUST be specified for enum substatements following the one"
+                                        + "with the current highest value");
+                                parserException.setLine(ctx.getStart().getLine());
+                                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                                throw parserException;
+                            } else if (maxValue <= curEnum.getValue()) {
+                                maxValue = curEnum.getValue();
+                                isValuePresent = true;
+                            }
+                        }
+                        if (isValuePresent) {
+                            maxValue++;
+                        }
+                        ((YangEnum) tmpEnumNode).setValue(maxValue);
+                    }
+                    try {
+                        yangEnumeration.addEnumInfo((YangEnum) tmpEnumNode);
+                    } catch (DataModelException e) {
+                        ParserException parserException = new ParserException(constructExtendedListenerErrorMessage(
+                                DUPLICATE_ENTRY, ENUM_DATA, ctx.string().getText(), EXIT, e.getMessage()));
+                        parserException.setLine(ctx.getStart().getLine());
+                        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                        throw parserException;
+                    }
+                    break;
+                }
+                default:
+                    throw new ParserException(
+                            constructListenerErrorMessage(INVALID_HOLDER, ENUM_DATA, ctx.string().getText(), EXIT));
+            }
+        } else {
+            throw new ParserException(
+                    constructListenerErrorMessage(MISSING_CURRENT_HOLDER, ENUM_DATA, ctx.string().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumerationListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumerationListener.java
new file mode 100644
index 0000000..5eff217
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/EnumerationListener.java
@@ -0,0 +1,228 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * type-body-stmts     = numerical-restrictions /
+ *                       decimal64-specification /
+ *                      string-restrictions /
+ *                       enum-specification /
+ *                       leafref-specification /
+ *                       identityref-specification /
+ *                       instance-identifier-specification /
+ *                       bits-specification /
+ *                       union-specification
+ *
+ * enum-specification  = 1*(enum-stmt stmtsep)
+ *
+ * ANTLR grammar rule
+ *
+ * typeBodyStatements : numericalRestrictions | stringRestrictions | enumSpecification
+ *                 | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+ *                 | bitsSpecification | unionSpecification;
+ *
+ * enumSpecification : enumStatement+;
+ */
+
+import org.onosproject.yangutils.datamodel.YangEnumeration;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.YangUnion;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ENUMERATION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangEnumerationNode;
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "enumeration" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class EnumerationListener {
+
+    /**
+     * Suffix to be used while creating enumeration class.
+     */
+    private static final String ENUMERATION_CLASS_SUFFIX = "_enum";
+
+    /**
+     * Creates a new enumeration listener.
+     */
+    private EnumerationListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (enumeration), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processEnumerationEntry(TreeWalkListener listener,
+                                               GeneratedYangParser.EnumSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUMERATION_DATA, "", ENTRY);
+
+        if (listener.getParsedDataStack().peek() instanceof YangType) {
+            YangEnumeration enumerationNode = getYangEnumerationNode(JAVA_GENERATION);
+            enumerationNode.setLineNumber(ctx.getStart().getLine());
+            enumerationNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+            enumerationNode.setFileName(listener.getFileName());
+            Parsable typeData = listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUMERATION_DATA, "", ENTRY);
+
+            Parsable tmpData = listener.getParsedDataStack().peek();
+
+            switch (tmpData.getYangConstructType()) {
+                case LEAF_DATA:
+                    // Set the name of enumeration same as leaf.
+                    enumerationNode.setName(((YangLeaf) tmpData).getName() + ENUMERATION_CLASS_SUFFIX);
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leaf = listener.getParsedDataStack().pop();
+                    // Add the enumeration node to the parent holder of leaf.
+                    addChildToParentNode(listener, enumerationNode);
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leaf);
+                    break;
+                case LEAF_LIST_DATA:
+                    // Set the name of enumeration same as leaf list.
+                    enumerationNode.setName(((YangLeafList) tmpData).getName() + ENUMERATION_CLASS_SUFFIX);
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leafList = listener.getParsedDataStack().pop();
+                    // Add the enumeration node to the parent holder of leaf.
+                    addChildToParentNode(listener, enumerationNode);
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leafList);
+                    break;
+                case UNION_DATA:
+                    YangUnion yangUnion = (YangUnion) tmpData;
+                    /*
+                     * In case parent of enumeration is a union, name of the
+                     * enumeration is parent union name suffixed with running
+                     * integer number, this is done because under union there
+                     * could be multiple child union types.
+                     */
+                    enumerationNode.setName(yangUnion.getName() + ENUMERATION_CLASS_SUFFIX
+                            + yangUnion.getChildUnionNumber());
+                    // Increment the running number.
+                    yangUnion.setChildUnionNumber(yangUnion.getChildUnionNumber() + 1);
+                    // Add union as a child to parent union.
+                    addChildToParentNode(listener, enumerationNode);
+                    break;
+                case TYPEDEF_DATA:
+                    YangTypeDef typeDef = (YangTypeDef) tmpData;
+                    // Set the name of enumeration same as typedef name.
+                    enumerationNode.setName(typeDef.getName() + ENUMERATION_CLASS_SUFFIX);
+                    // Add enumeration as a child to parent type def.
+                    addChildToParentNode(listener, enumerationNode);
+                    break;
+                // TODO deviate.
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                            ((YangType<?>) typeData).getDataTypeName(), ENTRY));
+            }
+            listener.getParsedDataStack().push(typeData);
+            listener.getParsedDataStack().push(enumerationNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ENUMERATION_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (enumeration), it
+     * perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processEnumerationExit(TreeWalkListener listener,
+            GeneratedYangParser.EnumSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUMERATION_DATA, "", EXIT);
+
+        Parsable tmpEnumerationNode = listener.getParsedDataStack().peek();
+        if (tmpEnumerationNode instanceof YangEnumeration) {
+            YangEnumeration enumerationNode = (YangEnumeration) tmpEnumerationNode;
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, ENUMERATION_DATA, "", EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case TYPE_DATA: {
+                    YangType<YangEnumeration> typeNode = (YangType<YangEnumeration>) tmpNode;
+                    typeNode.setDataTypeExtendedInfo(enumerationNode);
+                    break;
+                }
+                default:
+                    throw new ParserException(
+                            constructListenerErrorMessage(INVALID_HOLDER, ENUMERATION_DATA, "", EXIT));
+            }
+        } else {
+            throw new ParserException(
+                    constructListenerErrorMessage(MISSING_CURRENT_HOLDER, ENUMERATION_DATA, "", EXIT));
+        }
+    }
+
+    /**
+     * Adds the enumeration node to the parent holder.
+     *
+     * @param listener listener's object
+     * @param enumerationNode enumeration node which needs to be added to parent
+     */
+    private static void addChildToParentNode(TreeWalkListener listener, YangEnumeration enumerationNode) {
+        if (!(listener.getParsedDataStack().peek() instanceof YangNode)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ENUMERATION_DATA,
+                    "", ENTRY));
+        } else {
+            YangNode curNode = (YangNode) listener.getParsedDataStack().peek();
+            try {
+                curNode.addChild(enumerationNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        YangConstructType.ENUMERATION_DATA, "", ENTRY, e.getMessage()));
+            }
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorAppTagListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorAppTagListener.java
new file mode 100644
index 0000000..64f718b
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorAppTagListener.java
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAppErrorHolder;
+import org.onosproject.yangutils.datamodel.YangAppErrorInfo;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ERROR_APP_TAG_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC 6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC 6020
+ *
+ *  error-app-tag-stmt  = error-app-tag-keyword sep string stmtend
+ *
+ * ANTLR grammar rule
+ * errorAppTagStatement : ERROR_APP_TAG_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * error app tag defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class ErrorAppTagListener {
+
+    /**
+     * Creates a new error app tag listener.
+     */
+    private ErrorAppTagListener() {
+    }
+
+    /**
+     * Performs validations and updates the data model tree. It is called when parser
+     * receives an input matching the grammar rule error app tag.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processErrorAppTagMessageEntry(TreeWalkListener listener,
+                                                GeneratedYangParser.ErrorAppTagStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ERROR_APP_TAG_DATA, ctx.string().getText(), ENTRY);
+        String errorMessage = removeQuotesAndHandleConcat(ctx.string().getText());
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangAppErrorHolder) {
+            YangAppErrorInfo yangAppErrorInfo = ((YangAppErrorHolder) tmpNode).getAppErrorInfo();
+            yangAppErrorInfo.setErrorAppTag(errorMessage);
+
+            yangAppErrorInfo.setLineNumber(ctx.getStart().getLine());
+            yangAppErrorInfo.setCharPosition(ctx.getStart().getCharPositionInLine());
+            yangAppErrorInfo.setFileName(listener.getFileName());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ERROR_APP_TAG_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListener.java
new file mode 100644
index 0000000..ead1746
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ErrorMessageListener.java
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAppErrorHolder;
+import org.onosproject.yangutils.datamodel.YangAppErrorInfo;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ERROR_MESSAGE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ *  error-message-stmt  = error-message-keyword sep string stmtend
+ *
+ * ANTLR grammar rule
+ * errorMessageStatement : ERROR_MESSAGE_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * app error message defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class ErrorMessageListener {
+
+    /**
+     * Creates a new must listener.
+     */
+    private ErrorMessageListener() {
+    }
+
+    /**
+     * Performs validations and updates the data model tree. It is called when parser
+     * receives an input matching the grammar rule (app error message).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processErrorMessageEntry(TreeWalkListener listener,
+                                                GeneratedYangParser.ErrorMessageStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ERROR_MESSAGE_DATA, ctx.string().getText(), ENTRY);
+        String errorMessage = removeQuotesAndHandleConcat(ctx.string().getText());
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangAppErrorHolder) {
+            YangAppErrorInfo yangAppErrorInfo = ((YangAppErrorHolder) tmpNode).getAppErrorInfo();
+            yangAppErrorInfo.setErrorMessage(errorMessage);
+
+            yangAppErrorInfo.setLineNumber(ctx.getStart().getLine());
+            yangAppErrorInfo.setCharPosition(ctx.getStart().getCharPositionInLine());
+            yangAppErrorInfo.setFileName(listener.getFileName());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ERROR_MESSAGE_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java
new file mode 100644
index 0000000..9a1180f
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangExtension;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.EXTENSION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * extension-stmt      = extension-keyword sep identifier-arg-str optsep
+ *                       (";" /
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [argument-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                        "}")
+ *
+ * ANTLR grammar rule
+ * extensionStatement : EXTENSION_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE extensionBody RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "extension"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ExtensionListener {
+
+    /**
+     * Creates a new extension listener.
+     */
+    private ExtensionListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser
+     * receives an input matching the grammar rule (extension).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processExtensionEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.ExtensionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, EXTENSION_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), EXTENSION_DATA, ctx);
+
+        YangExtension extension = new YangExtension();
+
+        extension.setLineNumber(ctx.getStart().getLine());
+        extension.setCharPosition(ctx.getStart().getCharPositionInLine());
+        extension.setFileName(listener.getFileName());
+        extension.setName(identifier);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        switch (curData.getYangConstructType()) {
+            case MODULE_DATA:
+                YangModule module = ((YangModule) curData);
+                module.addExtension(extension);
+                break;
+            case SUB_MODULE_DATA:
+                YangSubModule subModule = ((YangSubModule) curData);
+                subModule.addExtension(extension);
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, EXTENSION_DATA,
+                        ctx.identifier().getText(), ENTRY));
+        }
+        listener.getParsedDataStack().push(extension);
+    }
+
+    /**
+     * Performs validation and updates the data model tree. It is called when parser exits
+     * from grammar rule(extension).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processExtensionExit(TreeWalkListener listener,
+                                            GeneratedYangParser.ExtensionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, EXTENSION_DATA, ctx.identifier().getText(), EXIT);
+
+        if (!(listener.getParsedDataStack().peek() instanceof YangExtension)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, EXTENSION_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FeatureListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FeatureListener.java
new file mode 100644
index 0000000..12e83b1
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FeatureListener.java
@@ -0,0 +1,122 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  feature-stmt        = feature-keyword sep identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             *(if-feature-stmt stmtsep)
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                         "}")
+ *
+ *
+ *
+ * ANTLR grammar rule
+ * featureStatement : FEATURE_KEYWORD string (STMTEND | LEFT_CURLY_BRACE featureBody RIGHT_CURLY_BRACE);
+ */
+
+import org.onosproject.yangutils.datamodel.YangFeature;
+import org.onosproject.yangutils.datamodel.YangFeatureHolder;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.FEATURE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "feature"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class FeatureListener {
+
+    /**
+     * Creates a new feature listener.
+     */
+    private FeatureListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree.It is called when parser receives
+     * an input matching the grammar rule (feature).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processFeatureEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.FeatureStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, FEATURE_DATA, ctx.string().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.string().getText(), FEATURE_DATA, ctx);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangFeatureHolder) {
+            YangFeatureHolder featureHolder = (YangFeatureHolder) tmpNode;
+
+            YangFeature feature = new YangFeature();
+            feature.setName(identifier);
+
+            feature.setLineNumber(ctx.getStart().getLine());
+            feature.setCharPosition(ctx.getStart().getCharPositionInLine());
+            feature.setFileName(listener.getFileName());
+            featureHolder.addFeatureList(feature);
+            listener.getParsedDataStack().push(feature);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, FEATURE_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Perform validations and updates the data model tree.It is called when parser exits from
+     * grammar rule(feature).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processFeatureExit(TreeWalkListener listener,
+                                          GeneratedYangParser.FeatureStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, FEATURE_DATA, ctx.string().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangFeature) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, FEATURE_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FractionDigitsListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FractionDigitsListener.java
new file mode 100644
index 0000000..baeb252
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/FractionDigitsListener.java
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * decimal64-specification = fraction-digits-stmt
+ *
+ * fraction-digits-stmt = fraction-digits-keyword sep
+ *                        fraction-digits-arg-str stmtend
+ *
+ * fraction-digits-arg-str = < a string that matches the rule
+ *                             fraction-digits-arg >
+ *
+ * fraction-digits-arg = ("1" ["0" / "1" / "2" / "3" / "4" /
+ *                              "5" / "6" / "7" / "8"])
+ *                       / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
+ *
+ * ANTLR grammar rule
+ * decimal64Specification : FRACTION_DIGITS_KEYWORD fraction STMTEND;
+ *
+ * fraction : string;
+ */
+
+import org.onosproject.yangutils.datamodel.YangDecimal64;
+import org.onosproject.yangutils.datamodel.YangRangeRestriction;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.FRACTION_DIGITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "fraction-digits"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class FractionDigitsListener {
+
+    /**
+     * Creates a new bit listener.
+     */
+    private FractionDigitsListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (fraction-digits), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processFractionDigitsEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.FractionDigitStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, FRACTION_DIGITS_DATA, ctx.fraction().getText(), ENTRY);
+
+        int value = getValidFractionDigits(ctx);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangType) {
+            YangType<YangDecimal64<YangRangeRestriction>> typeNode =
+                    (YangType<YangDecimal64<YangRangeRestriction>>) tmpNode;
+            YangDecimal64 decimal64Node = typeNode.getDataTypeExtendedInfo();
+            decimal64Node.setFractionDigit(value);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, FRACTION_DIGITS_DATA,
+                                                                    ctx.fraction().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Validate fraction digits.
+     *
+     * @param ctx context object of the grammar rule
+     * @return validated fraction-digits
+     */
+    public static int getValidFractionDigits(GeneratedYangParser.FractionDigitStatementContext ctx) {
+        String value = ctx.fraction().getText().trim();
+        ParserException parserException;
+
+        int fractionDigits = Integer.parseInt(value);
+        if ((fractionDigits >= YangDecimal64.MIN_FRACTION_DIGITS_VALUE) &&
+                (fractionDigits <= YangDecimal64.MAX_FRACTION_DIGITS_VALUE)) {
+            return fractionDigits;
+        } else {
+            parserException =
+                    new ParserException("YANG file error : fraction-digits value should be between 1 and 18.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java
new file mode 100644
index 0000000..46ca2e0
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java
@@ -0,0 +1,178 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.GROUPING_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangGroupingNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * grouping-stmt       = grouping-keyword sep identifier-arg-str optsep
+ *                      (";" /
+ *                       "{" stmtsep
+ *                          ;; these stmts can appear in any order
+ *                          [status-stmt stmtsep]
+ *                           [description-stmt stmtsep]
+ *                           [reference-stmt stmtsep]
+ *                           *((typedef-stmt /
+ *                              grouping-stmt) stmtsep)
+ *                           *(data-def-stmt stmtsep)
+ *                       "}")
+ *
+ * ANTLR grammar rule
+ * groupingStatement : GROUPING_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE
+ *       (statusStatement | descriptionStatement | referenceStatement | typedefStatement | groupingStatement
+ *       | dataDefStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "grouping"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class GroupingListener {
+
+    /**
+     * Creates a new grouping listener.
+     */
+    private GroupingListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (grouping), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processGroupingEntry(TreeWalkListener listener,
+                                            GeneratedYangParser.GroupingStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, GROUPING_DATA, ctx.identifier().getText(), ENTRY);
+
+        // Check validity of identifier and remove double quotes.
+        String identifier = getValidIdentifier(ctx.identifier().getText(), GROUPING_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Increase the grouping count by one.
+        listener.increaseGroupingDepth();
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, GROUPING_DATA);
+
+        if (curData instanceof YangModule || curData instanceof YangSubModule
+                || curData instanceof YangContainer || curData instanceof YangNotification
+                || curData instanceof YangList || curData instanceof YangGrouping
+                || curData instanceof YangRpc || curData instanceof YangInput
+                || curData instanceof YangOutput) {
+
+            YangGrouping groupingNode = getYangGroupingNode(JAVA_GENERATION);
+            groupingNode.setName(identifier);
+            groupingNode.setGroupingDepth(listener.getGroupingDepth());
+
+            groupingNode.setLineNumber(line);
+            groupingNode.setCharPosition(charPositionInLine);
+            groupingNode.setFileName(listener.getFileName());
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(groupingNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        GROUPING_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(groupingNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    GROUPING_DATA, ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (grouping), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processGroupingExit(TreeWalkListener listener,
+                                           GeneratedYangParser.GroupingStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, GROUPING_DATA, ctx.identifier().getText(), EXIT);
+
+        // Decrease the grouping count by one.
+        listener.decreaseGroupingDepth();
+        if (listener.getParsedDataStack().peek() instanceof YangGrouping) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, GROUPING_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of case sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.GroupingStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, GROUPING_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, GROUPING_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, GROUPING_DATA, ctx.identifier().getText());
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityListener.java
new file mode 100644
index 0000000..332ae4f
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityListener.java
@@ -0,0 +1,126 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangIdentity;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangIdentityNode;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.IDENTITY_DATA;
+
+/**
+ * Reference: RFC6020 and YANG ANTLR Grammar.
+ *
+ * ABNF grammar as per RFC6020
+ * identity-stmt       = identity-keyword sep identifier-arg-str optsep
+ *                       (";" /
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [base-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                        "}")
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "identity"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class IdentityListener {
+
+    //Creates a identity listener.
+    private IdentityListener() {
+    }
+
+    /**
+     * Performs validations and update the data model tree when parser receives an input
+     * matching the grammar rule (identity).
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIdentityEntry(TreeWalkListener listener,
+                                            GeneratedYangParser.IdentityStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IDENTITY_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), IDENTITY_DATA, ctx);
+
+        YangIdentity identity = getYangIdentityNode(JAVA_GENERATION);
+        identity.setName(identifier);
+
+        identity.setLineNumber(ctx.getStart().getLine());
+        identity.setCharPosition(ctx.getStart().getCharPositionInLine());
+        identity.setFileName(listener.getFileName());
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangSubModule) {
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(identity);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        IDENTITY_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            // Push identity node to the stack.
+            listener.getParsedDataStack().push(identity);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IDENTITY_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+
+    }
+
+    /**
+     * Performs validations and update the data model tree when parser exits from grammar
+     * rule (identity).
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIdentityExit(TreeWalkListener listener,
+                                           GeneratedYangParser.IdentityStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_CURRENT_HOLDER, IDENTITY_DATA, ctx.identifier().getText(), EXIT);
+
+        Parsable parsableType = listener.getParsedDataStack().pop();
+        if (!(parsableType instanceof YangIdentity)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IDENTITY_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityrefListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityrefListener.java
new file mode 100644
index 0000000..17f197a
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IdentityrefListener.java
@@ -0,0 +1,232 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangIdentityRef;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.UNRESOLVED;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.BASE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.IDENTITYREF_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNodeIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * identityref-specification =
+ *                        base-stmt stmtsep
+ * base-stmt           = base-keyword sep identifier-ref-arg-str
+ *                          optsep stmtend*
+ * identifier-ref-arg  = [prefix ":"] identifier
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "identityref"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class IdentityrefListener {
+
+    //Creates a new type listener.
+    private IdentityrefListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree when parser receives an input
+     * matching the grammar rule (identityref).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIdentityrefEntry(TreeWalkListener listener,
+                                               GeneratedYangParser.IdentityrefSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IDENTITYREF_DATA, "", ENTRY);
+
+        if (listener.getParsedDataStack().peek() instanceof YangType) {
+
+            YangIdentityRef identityRef = new YangIdentityRef();
+            Parsable typeData = listener.getParsedDataStack().pop();
+            YangDataTypes yangDataTypes = ((YangType) typeData).getDataType();
+            YangResolutionInfoImpl resolutionInfo;
+
+            // Validate node identifier.
+            YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(ctx.baseStatement().string().getText(),
+                    BASE_DATA, ctx);
+            identityRef.setBaseIdentity(nodeIdentifier);
+            ((YangType) typeData).setDataTypeExtendedInfo(identityRef);
+
+            int errorLine = ctx.getStart().getLine();
+            int errorPosition = ctx.getStart().getCharPositionInLine();
+
+            identityRef.setLineNumber(errorLine);
+            identityRef.setCharPosition(errorPosition);
+            identityRef.setFileName(listener.getFileName());
+            Parsable tmpData = listener.getParsedDataStack().peek();
+            switch (tmpData.getYangConstructType()) {
+                case LEAF_DATA:
+
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leaf = listener.getParsedDataStack().pop();
+                    Parsable parentNodeOfLeaf = listener.getParsedDataStack().peek();
+
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leaf);
+
+                    // Verify parent node of leaf
+                    if (!(parentNodeOfLeaf instanceof YangNode)) {
+                        throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                                IDENTITYREF_DATA, ctx.getText(), EXIT));
+                    }
+
+                    identityRef.setResolvableStatus(UNRESOLVED);
+
+                    if (listener.getGroupingDepth() == 0) {
+                        // Add resolution information to the list
+                        resolutionInfo = new YangResolutionInfoImpl<YangIdentityRef>(identityRef,
+                                (YangNode) parentNodeOfLeaf, errorLine, errorPosition);
+                        addToResolutionList(resolutionInfo, ctx);
+                    } else {
+                        identityRef.setInGrouping(true);
+                    }
+                    break;
+                case LEAF_LIST_DATA:
+
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leafList = listener.getParsedDataStack().pop();
+                    Parsable parentNodeOfLeafList = listener.getParsedDataStack().peek();
+
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leafList);
+
+                    // Verify parent node of leaf
+                    if (!(parentNodeOfLeafList instanceof YangNode)) {
+                        throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                                IDENTITYREF_DATA, ctx.getText(), EXIT));
+                    }
+
+                    identityRef.setResolvableStatus(UNRESOLVED);
+
+                    if (listener.getGroupingDepth() == 0) {
+                        // Add resolution information to the list
+                        resolutionInfo = new YangResolutionInfoImpl<YangIdentityRef>(identityRef,
+                                (YangNode) parentNodeOfLeafList, errorLine, errorPosition);
+                        addToResolutionList(resolutionInfo, ctx);
+                    } else {
+                        identityRef.setInGrouping(true);
+                    }
+                    break;
+                case UNION_DATA:
+
+                    Parsable parentNodeOfUnionNode = listener.getParsedDataStack().peek();
+
+                    // Verify parent node of leaf
+                    if (!(parentNodeOfUnionNode instanceof YangNode)) {
+                        throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                                IDENTITYREF_DATA, ctx.getText(), EXIT));
+                    }
+
+                    identityRef.setResolvableStatus(UNRESOLVED);
+
+                    if (listener.getGroupingDepth() == 0) {
+                        // Add resolution information to the list
+                        resolutionInfo = new YangResolutionInfoImpl<YangIdentityRef>(identityRef,
+                                (YangNode) parentNodeOfUnionNode, errorLine, errorPosition);
+                        addToResolutionList(resolutionInfo, ctx);
+                    } else {
+                        identityRef.setInGrouping(true);
+                    }
+                    break;
+                case TYPEDEF_DATA:
+                    if (listener.getGroupingDepth() != 0) {
+                        identityRef.setInGrouping(true);
+                    }
+                    /**
+                     * Do not add the identity ref to resolution list. It needs to be
+                     * added to resolution list, when leaf/leaf list references to
+                     * this typedef. At this time that leaf/leaf-list becomes the
+                     * parent for the identityref.
+                     */
+                    break;
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IDENTITYREF_DATA,
+                            ctx.getText(), EXIT));
+            }
+            listener.getParsedDataStack().push(typeData);
+            listener.getParsedDataStack().push(identityRef);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IDENTITYREF_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * Performs validations and update the data model tree when parser exits from grammar
+     * rule (identityref).
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIdentityrefExit(TreeWalkListener listener,
+                                              GeneratedYangParser.IdentityrefSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_CURRENT_HOLDER, IDENTITYREF_DATA, ctx.getText(), EXIT);
+
+        Parsable parsableType = listener.getParsedDataStack().pop();
+        if (!(parsableType instanceof YangIdentityRef)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IDENTITYREF_DATA,
+                    ctx.getText(), EXIT));
+        }
+    }
+
+    /**
+     * Adds to resolution list.
+     *
+     * @param resolutionInfo resolution information
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangIdentityRef> resolutionInfo,
+                                            GeneratedYangParser.IdentityrefSpecificationContext ctx) {
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    IDENTITYREF_DATA, ctx.getText(), ENTRY, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IfFeatureListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IfFeatureListener.java
new file mode 100644
index 0000000..ab11780
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IfFeatureListener.java
@@ -0,0 +1,147 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ * if-feature-stmt     = if-feature-keyword sep identifier-ref-arg-str
+ *                        optsep stmtend
+ *
+ * ANTLR grammar rule
+ * ifFeatureStatement : IF_FEATURE_KEYWORD string STMTEND;
+ */
+
+import org.onosproject.yangutils.datamodel.YangFeature;
+import org.onosproject.yangutils.datamodel.YangIfFeature;
+import org.onosproject.yangutils.datamodel.YangIfFeatureHolder;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.YangResolutionInfo;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.UNRESOLVED;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.IF_FEATURE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNodeIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "if-feature"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class IfFeatureListener {
+
+    /**
+     * Creates a new IfFeature listener.
+     */
+    private IfFeatureListener() {
+    }
+
+    /**
+     * Performs validation and updates the data model tree.It is called when parser receives
+     * an input matching the grammar rule (if-feature).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIfFeatureEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.IfFeatureStatementContext ctx) {
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IF_FEATURE_DATA, ctx.string().getText(), ENTRY);
+
+        // Validate if-feature argument string
+        YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(ctx.string().getText(),
+                IF_FEATURE_DATA, ctx);
+
+        YangIfFeature ifFeature = new YangIfFeature();
+        ifFeature.setName(nodeIdentifier);
+        ifFeature.setResolvableStatus(UNRESOLVED);
+
+        ifFeature.setLineNumber(ctx.getStart().getLine());
+        ifFeature.setCharPosition(ctx.getStart().getCharPositionInLine());
+        ifFeature.setFileName(listener.getFileName());
+        YangIfFeatureHolder ifFeatureHolder;
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangIfFeatureHolder) {
+            ifFeatureHolder = (YangIfFeatureHolder) tmpNode;
+            ifFeatureHolder.addIfFeatureList(ifFeature);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IF_FEATURE_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+
+        // Add resolution information to the list
+        Parsable parentNode;
+        if (tmpNode instanceof YangLeafList || tmpNode instanceof YangLeaf
+                || tmpNode instanceof YangFeature) {
+            Parsable leafData = listener.getParsedDataStack().pop();
+            parentNode = listener.getParsedDataStack().peek();
+            listener.getParsedDataStack().push(leafData);
+        } else {
+            parentNode = tmpNode;
+        }
+
+        // Verify parent node of leaf
+        if (!(parentNode instanceof YangNode)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IF_FEATURE_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+        YangResolutionInfoImpl resolutionInfo = new YangResolutionInfoImpl<YangIfFeature>(ifFeature,
+                (YangNode) parentNode, errorLine,
+                errorPosition);
+        addToResolutionList(resolutionInfo, ctx);
+    }
+
+    /**
+     * Add to resolution list.
+     *
+     * @param resolutionInfo resolution information.
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfo<YangIfFeature> resolutionInfo,
+                                            GeneratedYangParser.IfFeatureStatementContext ctx) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    IF_FEATURE_DATA, ctx.string().getText(), EXIT, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
new file mode 100644
index 0000000..1f7a7d7
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ImportListener.java
@@ -0,0 +1,141 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangImport;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.IMPORT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * linkage-stmts       = ;; these stmts can appear in any order
+ *                       *(import-stmt stmtsep)
+ *                       *(include-stmt stmtsep)
+ *
+ * import-stmt         = import-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           prefix-stmt stmtsep
+ *                           [revision-date-stmt stmtsep]
+ *                        "}"
+ *
+ * ANTLR grammar rule
+ * linkage_stmts : (import_stmt
+ *               | include_stmt)*;
+ * import_stmt : IMPORT_KEYWORD identifier LEFT_CURLY_BRACE import_stmt_body
+ *               RIGHT_CURLY_BRACE;
+ * import_stmt_body : prefix_stmt revision_date_stmt?;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "import"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ImportListener {
+
+    /**
+     * Creates a new import listener.
+     */
+    private ImportListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (import), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processImportEntry(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), IMPORT_DATA, ctx);
+
+        YangImport importNode = new YangImport();
+        importNode.setModuleName(identifier);
+
+        // Set the line number and character position in line for the belongs to.
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+        importNode.setLineNumber(errorLine);
+        importNode.setCharPosition(errorPosition);
+        importNode.setFileName(listener.getFileName());
+
+        // Push import node to the stack.
+        listener.getParsedDataStack().push(importNode);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (import), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processImportExit(TreeWalkListener listener, GeneratedYangParser.ImportStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.identifier().getText(), EXIT);
+
+        Parsable tmpImportNode = listener.getParsedDataStack().peek();
+        if (tmpImportNode instanceof YangImport) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, IMPORT_DATA, ctx.identifier().getText(),
+                    EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case MODULE_DATA: {
+                    YangModule module = (YangModule) tmpNode;
+                    module.addToImportList((YangImport) tmpImportNode);
+                    break;
+                }
+                case SUB_MODULE_DATA: {
+                    YangSubModule subModule = (YangSubModule) tmpNode;
+                    subModule.addToImportList((YangImport) tmpImportNode);
+                    break;
+                }
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, IMPORT_DATA,
+                            ctx.identifier().getText(),
+                            EXIT));
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, IMPORT_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java
new file mode 100644
index 0000000..5842a7e
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/IncludeListener.java
@@ -0,0 +1,140 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangInclude;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.INCLUDE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * linkage-stmts       = ;; these stmts can appear in any order
+ *                       *(import-stmt stmtsep)
+ *                       *(include-stmt stmtsep)
+ *
+ * include-stmt        = include-keyword sep identifier-arg-str optsep
+ *                             (";" /
+ *                              "{" stmtsep
+ *                                  [revision-date-stmt stmtsep]
+ *                            "}")
+ *
+ * ANTLR grammar rule
+ * linkage_stmts : (import_stmt
+ *               | include_stmt)*;
+ * include_stmt : INCLUDE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE
+ *                revision_date_stmt? RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "include"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class IncludeListener {
+
+    /**
+     * Creates a new include listener.
+     */
+    private IncludeListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (include), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIncludeEntry(TreeWalkListener listener, GeneratedYangParser.IncludeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.identifier().getText(),
+                ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), INCLUDE_DATA, ctx);
+
+        YangInclude includeNode = new YangInclude();
+        includeNode.setSubModuleName(identifier);
+
+        // Set the line number and character position in line for the belongs to.
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+        includeNode.setLineNumber(errorLine);
+        includeNode.setCharPosition(errorPosition);
+        includeNode.setFileName(listener.getFileName());
+
+        listener.getParsedDataStack().push(includeNode);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (include), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processIncludeExit(TreeWalkListener listener, GeneratedYangParser.IncludeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.identifier().getText(), EXIT);
+
+        Parsable tmpIncludeNode = listener.getParsedDataStack().peek();
+        if (tmpIncludeNode instanceof YangInclude) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, INCLUDE_DATA, ctx.identifier().getText(),
+                    EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case MODULE_DATA: {
+                    YangModule module = (YangModule) tmpNode;
+                    module.addToIncludeList((YangInclude) tmpIncludeNode);
+                    break;
+                }
+                case SUB_MODULE_DATA: {
+                    YangSubModule subModule = (YangSubModule) tmpNode;
+                    subModule.addToIncludeList((YangInclude) tmpIncludeNode);
+                    break;
+                }
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, INCLUDE_DATA,
+                            ctx.identifier().getText(),
+                            EXIT));
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, INCLUDE_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/InputListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/InputListener.java
new file mode 100644
index 0000000..0b7e116
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/InputListener.java
@@ -0,0 +1,131 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.INPUT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangInputNode;
+import static org.onosproject.yangutils.utils.UtilConstants.INPUT;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ * input-stmt          = input-keyword optsep
+ *                       "{" stmtsep
+ *                           ;; these stmts can appear in any order
+ *                           *((typedef-stmt /
+ *                              grouping-stmt) stmtsep)
+ *                           1*(data-def-stmt stmtsep)
+ *                         "}"
+ *
+ * inputStatement : INPUT_KEYWORD LEFT_CURLY_BRACE inputStatementBody RIGHT_CURLY_BRACE;
+
+ * inputStatementBody : typedefStatement* dataDefStatement+
+ *                    | dataDefStatement+ typedefStatement*
+ *                    | groupingStatement* dataDefStatement+
+ *                    | dataDefStatement+ groupingStatement*;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "input"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class InputListener {
+
+    /**
+     * Creates a new input listener.
+     */
+    private InputListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (input), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processInputEntry(TreeWalkListener listener,
+                                         GeneratedYangParser.InputStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INPUT_DATA, "", ENTRY);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangRpc) {
+
+            YangInput yangInput = getYangInputNode(JAVA_GENERATION);
+            yangInput.setName(INPUT);
+            yangInput.setLineNumber(ctx.getStart().getLine());
+            yangInput.setCharPosition(ctx.getStart().getCharPositionInLine());
+            yangInput.setFileName(listener.getFileName());
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(yangInput);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        INPUT_DATA, "", ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(yangInput);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, INPUT_DATA,
+                    "", ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (input), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processInputExit(TreeWalkListener listener,
+                                        GeneratedYangParser.InputStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, INPUT_DATA, "", EXIT);
+
+        if (!(listener.getParsedDataStack().peek() instanceof YangInput)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, INPUT_DATA,
+                    "", EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java
new file mode 100644
index 0000000..889de0a
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java
@@ -0,0 +1,99 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.KEY_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * key-stmt            = key-keyword sep key-arg-str stmtend
+ *
+ * ANTLR grammar rule
+ * keyStatement : KEY_KEYWORD key STMTEND;
+ * key          : string;
+ */
+
+/**
+ * Represesnts listener based call back function corresponding to the "key" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class KeyListener {
+
+    /**
+     * Creates a new key listener.
+     */
+    private KeyListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (key), perform validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processKeyEntry(TreeWalkListener listener,
+            GeneratedYangParser.KeyStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, KEY_DATA, ctx.key().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (listener.getParsedDataStack().peek() instanceof YangList) {
+            YangList yangList = (YangList) tmpData;
+            String tmpKeyValue = removeQuotesAndHandleConcat(ctx.key().getText());
+            if (tmpKeyValue.contains(" ")) {
+                String[] keyValues = tmpKeyValue.split(" ");
+                for (String keyValue : keyValues) {
+                    try {
+                        yangList.addKey(keyValue);
+                    } catch (DataModelException e) {
+                        throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA, KEY_DATA,
+                                ctx.key().getText(), ENTRY, e.getMessage()));
+                    }
+                }
+            } else {
+                try {
+                    yangList.addKey(tmpKeyValue);
+                } catch (DataModelException e) {
+                    throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA, KEY_DATA,
+                            ctx.key().getText(), ENTRY, e.getMessage()));
+                }
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, KEY_DATA, ctx.key().getText(),
+                    ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListListener.java
new file mode 100644
index 0000000..8dd33b8
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListListener.java
@@ -0,0 +1,181 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangLeavesHolder;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.LEAF_LIST_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MAX_ELEMENT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MIN_ELEMENT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityEqualsOne;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangLeafList;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  leaf-list-stmt      = leaf-list-keyword sep identifier-arg-str optsep
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [when-stmt stmtsep]
+ *                            *(if-feature-stmt stmtsep)
+ *                            type-stmt stmtsep
+ *                            [units-stmt stmtsep]
+ *                            *(must-stmt stmtsep)
+ *                            [config-stmt stmtsep]
+ *                            [min-elements-stmt stmtsep]
+ *                            [max-elements-stmt stmtsep]
+ *                            [ordered-by-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ *  leafListStatement : LEAF_LIST_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement |
+ *  typeStatement | unitsStatement | mustStatement | configStatement | minElementsStatement | maxElementsStatement |
+ *  orderedByStatement | statusStatement | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "leaf-list"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class LeafListListener {
+
+    /**
+     * Creates a new leaf list listener.
+     */
+    private LeafListListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (leaf-list), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafListEntry(TreeWalkListener listener,
+                                            GeneratedYangParser.LeafListStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LEAF_LIST_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), LEAF_LIST_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, LEAF_LIST_DATA);
+
+        YangLeafList leafList = getYangLeafList(JAVA_GENERATION);
+        leafList.setName(identifier);
+        leafList.setLineNumber(line);
+        leafList.setCharPosition(charPositionInLine);
+        leafList.setFileName(listener.getFileName());
+        /*
+         * If "config" is not specified, the default is the same as the parent
+         * schema node's "config" value.
+         */
+        if (ctx.configStatement().isEmpty()) {
+            boolean parentConfig = ListenerValidation.getParentNodeConfig(listener);
+            leafList.setConfig(parentConfig);
+        }
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        YangLeavesHolder leavesHolder;
+
+        if (tmpData instanceof YangLeavesHolder) {
+            leavesHolder = (YangLeavesHolder) tmpData;
+            leavesHolder.addLeafList(leafList);
+            leafList.setContainedIn(leavesHolder);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAF_LIST_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+        listener.getParsedDataStack().push(leafList);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (leaf-list), it performs
+     * validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafListExit(TreeWalkListener listener,
+                                           GeneratedYangParser.LeafListStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LEAF_LIST_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangLeafList) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, LEAF_LIST_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of leaf-list sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.LeafListStatementContext ctx) {
+
+        validateCardinalityEqualsOne(ctx.typeStatement(), TYPE_DATA, LEAF_LIST_DATA, ctx.identifier().getText(), ctx);
+        validateCardinalityMaxOne(ctx.unitsStatement(), UNITS_DATA, LEAF_LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.configStatement(), CONFIG_DATA, LEAF_LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.maxElementsStatement(), MAX_ELEMENT_DATA, LEAF_LIST_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.minElementsStatement(), MIN_ELEMENT_DATA, LEAF_LIST_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, LEAF_LIST_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, LEAF_LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, LEAF_LIST_DATA, ctx.identifier().getText());
+        //TODO ordered by
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListener.java
new file mode 100644
index 0000000..d6f06ff
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafListener.java
@@ -0,0 +1,190 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Implements listener based call back function corresponding to the "leaf"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeavesHolder;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.LEAF_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MANDATORY_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CONTENT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityEqualsOne;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangLeaf;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  leaf-stmt           = leaf-keyword sep identifier-arg-str optsep
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [when-stmt stmtsep]
+ *                            *(if-feature-stmt stmtsep)
+ *                            type-stmt stmtsep
+ *                            [units-stmt stmtsep]
+ *                            *(must-stmt stmtsep)
+ *                            [default-stmt stmtsep]
+ *                            [config-stmt stmtsep]
+ *                            [mandatory-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ *  leafStatement : LEAF_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | typeStatement |
+ *  unitsStatement | mustStatement | defaultStatement | configStatement | mandatoryStatement | statusStatement  |
+ *  descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "leaf" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class LeafListener {
+
+    /**
+     * Creates a new leaf listener.
+     */
+    private LeafListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (leaf), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.LeafStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LEAF_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), LEAF_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, LEAF_DATA);
+
+        YangLeaf leaf = getYangLeaf(JAVA_GENERATION);
+        leaf.setName(identifier);
+        leaf.setLineNumber(line);
+        leaf.setCharPosition(charPositionInLine);
+        leaf.setFileName(listener.getFileName());
+
+        /*
+         * If "config" is not specified, the default is the same as the parent
+         * schema node's "config" value.
+         */
+        if (ctx.configStatement().isEmpty()) {
+            boolean parentConfig = ListenerValidation.getParentNodeConfig(listener);
+            leaf.setConfig(parentConfig);
+        }
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        YangLeavesHolder leavesHolder;
+
+        if (tmpData instanceof YangLeavesHolder) {
+            leavesHolder = (YangLeavesHolder) tmpData;
+            leavesHolder.addLeaf(leaf);
+            leaf.setContainedIn(leavesHolder);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAF_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+
+        listener.getParsedDataStack().push(leaf);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (leaf), performs
+     * validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafExit(TreeWalkListener listener,
+                                       GeneratedYangParser.LeafStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LEAF_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangLeaf) {
+            YangLeaf leafNode = (YangLeaf) listener.getParsedDataStack().peek();
+            try {
+                leafNode.validateDataOnExit();
+            } catch (DataModelException e) {
+                throw new ParserException(constructListenerErrorMessage(INVALID_CONTENT, LEAF_DATA,
+                        ctx.identifier().getText(), EXIT));
+            }
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, LEAF_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of leaf sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.LeafStatementContext ctx) {
+
+        validateCardinalityEqualsOne(ctx.typeStatement(), TYPE_DATA, LEAF_DATA, ctx.identifier().getText(), ctx);
+        validateCardinalityMaxOne(ctx.unitsStatement(), UNITS_DATA, LEAF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.configStatement(), CONFIG_DATA, LEAF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.mandatoryStatement(), MANDATORY_DATA, LEAF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, LEAF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, LEAF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, LEAF_DATA, ctx.identifier().getText());
+        //TODO when.
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafrefListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafrefListener.java
new file mode 100644
index 0000000..25ac31c
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LeafrefListener.java
@@ -0,0 +1,229 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangLeafRef;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.UNRESOLVED;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.LEAFREF_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * type-body-stmts     = numerical-restrictions /
+ *                       decimal64-specification /
+ *                       string-restrictions /
+ *                       enum-specification /
+ *                       leafref-specification /
+ *                       identityref-specification /
+ *                       instance-identifier-specification /
+ *                       bits-specification /
+ *                       union-specification
+ *
+ * leafref-specification =
+ *                         ;; these stmts can appear in any order
+ *                        path-stmt stmtsep
+ *                        [require-instance-stmt stmtsep]
+ *
+ * ANTLR grammar rule
+ *
+ * typeBodyStatements : numericalRestrictions | stringRestrictions | enumSpecification
+ *                 | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+ *                 | bitsSpecification | unionSpecification;
+ *
+ * leafrefSpecification : (pathStatement (requireInstanceStatement)?) | ((requireInstanceStatement)? pathStatement);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "leafref" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class LeafrefListener {
+
+    /**
+     * Creates a new leafref listener.
+     */
+    private LeafrefListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (leafref), perform validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafrefEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.LeafrefSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LEAFREF_DATA, "", ENTRY);
+
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+
+        YangLeafRef<?> leafRef = new YangLeafRef<>();
+
+        leafRef.setLineNumber(errorLine);
+        leafRef.setCharPosition(errorPosition);
+        leafRef.setFileName(listener.getFileName());
+        Parsable typeData = listener.getParsedDataStack().pop();
+
+        if (!(typeData instanceof YangType)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAFREF_DATA,
+                    "", ENTRY));
+        }
+
+        YangType type = (YangType) typeData;
+        type.setDataTypeExtendedInfo(leafRef);
+
+        // Setting by default the value of require-instance as true.
+        leafRef.setRequireInstance(true);
+        Parsable tmpData = listener.getParsedDataStack().peek();
+
+        switch (tmpData.getYangConstructType()) {
+
+            case LEAF_DATA:
+
+                // Parent YANG node of leaf to be added in resolution information.
+                YangLeaf leaf = (YangLeaf) listener.getParsedDataStack().pop();
+                Parsable parentNodeOfLeaf = listener.getParsedDataStack().peek();
+                listener.getParsedDataStack().push(leaf);
+
+                // Verify parent node of leaf.
+                if (!(parentNodeOfLeaf instanceof YangNode)) {
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAFREF_DATA,
+                            "", ENTRY));
+                }
+
+                leafRef.setResolvableStatus(UNRESOLVED);
+                leafRef.setParentNodeOfLeafref((YangNode) parentNodeOfLeaf);
+                if (listener.getGroupingDepth() == 0) {
+                    // Add resolution information to the list.
+                    YangResolutionInfoImpl resolutionInfo = new YangResolutionInfoImpl<YangLeafRef>(leafRef,
+                            (YangNode) parentNodeOfLeaf, errorLine, errorPosition);
+                    addToResolutionList(resolutionInfo);
+                } else {
+                    leafRef.setInGrouping(true);
+                }
+                break;
+
+            case LEAF_LIST_DATA:
+
+                // Parent YANG node of leaf-list to be added in resolution information.
+                YangLeafList leafList = (YangLeafList) listener.getParsedDataStack().pop();
+                Parsable parentNodeOfLeafList = listener.getParsedDataStack().peek();
+                listener.getParsedDataStack().push(leafList);
+
+                // Verify parent node of leaf-list.
+                if (!(parentNodeOfLeafList instanceof YangNode)) {
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAFREF_DATA,
+                            "", ENTRY));
+                }
+
+                leafRef.setResolvableStatus(UNRESOLVED);
+                leafRef.setParentNodeOfLeafref((YangNode) parentNodeOfLeafList);
+
+                if (listener.getGroupingDepth() == 0) {
+                    // Add resolution information to the list.
+                    YangResolutionInfoImpl resolutionInfoImpl = new YangResolutionInfoImpl<YangLeafRef>(leafRef,
+                            (YangNode) parentNodeOfLeafList, errorLine, errorPosition);
+                    addToResolutionList(resolutionInfoImpl);
+                } else {
+                    leafRef.setInGrouping(true);
+                }
+                break;
+
+            case TYPEDEF_DATA:
+                Parsable parentNodeOfLeafref = listener.getParsedDataStack().peek();
+                leafRef.setParentNodeOfLeafref((YangNode) parentNodeOfLeafref);
+                if (listener.getGroupingDepth() != 0) {
+                    leafRef.setInGrouping(true);
+                }
+                /*
+                 * Do not add the leaf ref to resolution list. It needs to be
+                 * added to resolution list, when leaf/leaf list references to
+                 * this typedef. At this time that leaf/leaf-list becomes the
+                 * parent for the leafref.
+                 */
+                break;
+
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAFREF_DATA,
+                        "", ENTRY));
+        }
+        listener.getParsedDataStack().push(typeData);
+        listener.getParsedDataStack().push(leafRef);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (leafref), it performs
+     * validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLeafrefExit(TreeWalkListener listener,
+                                          GeneratedYangParser.LeafrefSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_CURRENT_HOLDER, LEAFREF_DATA, "", EXIT);
+
+        Parsable parsableType = listener.getParsedDataStack().pop();
+        if (!(parsableType instanceof YangLeafRef)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LEAFREF_DATA,
+                    "", EXIT));
+        }
+    }
+
+    /**
+     * Adds to resolution list.
+     *
+     * @param resolutionInfo resolution information
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl resolutionInfo) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    LEAFREF_DATA, "", ENTRY, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LengthRestrictionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LengthRestrictionListener.java
new file mode 100644
index 0000000..52b7143
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/LengthRestrictionListener.java
@@ -0,0 +1,179 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangDerivedInfo;
+import org.onosproject.yangutils.datamodel.YangRangeRestriction;
+import org.onosproject.yangutils.datamodel.YangStringRestriction;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.BINARY;
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.DERIVED;
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.STRING;
+import static org.onosproject.yangutils.datamodel.utils.RestrictionResolver.processLengthRestriction;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.LENGTH_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  length-stmt         = length-keyword sep length-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [error-message-stmt stmtsep]
+ *                             [error-app-tag-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ *
+ * ANTLR grammar rule
+ * lengthStatement : LENGTH_KEYWORD length
+ *                 (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "length"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class LengthRestrictionListener {
+
+    /**
+     * Creates a new length restriction listener.
+     */
+    private LengthRestrictionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (length), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLengthRestrictionEntry(TreeWalkListener listener,
+                                                     GeneratedYangParser.LengthStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LENGTH_DATA, ctx.length().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData.getYangConstructType() == TYPE_DATA) {
+            YangType type = (YangType) tmpData;
+            setLengthRestriction(listener, type, ctx);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LENGTH_DATA,
+                    ctx.length().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Sets the length restriction to type.
+     *
+     * @param listener listener's object
+     * @param type     Yang type for which length restriction to be set
+     * @param ctx      context object of the grammar rule
+     */
+    private static void setLengthRestriction(TreeWalkListener listener, YangType type,
+                                             GeneratedYangParser.LengthStatementContext ctx) {
+
+        if (type.getDataType() == DERIVED) {
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setLengthRestrictionString(ctx.length().getText());
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setLineNumber(ctx.getStart().getLine());
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setCharPosition(ctx.getStart().getCharPositionInLine());
+            return;
+        }
+
+        if (type.getDataType() != STRING && type.getDataType() != BINARY) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(LENGTH_DATA) + " name " + ctx.length().getText() +
+                    " can be used to restrict the built-in type string/binary or types derived from string/binary.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        YangRangeRestriction lengthRestriction = null;
+        try {
+            lengthRestriction = processLengthRestriction(null, ctx.getStart().getLine(),
+                    ctx.getStart().getCharPositionInLine(), false, ctx.length().getText());
+        } catch (DataModelException e) {
+            ParserException parserException = new ParserException(e.getMessage());
+            parserException.setCharPosition(e.getCharPositionInLine());
+            parserException.setLine(e.getLineNumber());
+            throw parserException;
+        }
+
+        if (type.getDataType() == STRING) {
+            YangStringRestriction stringRestriction = (YangStringRestriction) type.getDataTypeExtendedInfo();
+            if (stringRestriction == null) {
+                stringRestriction = new YangStringRestriction();
+                type.setDataTypeExtendedInfo(stringRestriction);
+            }
+
+            stringRestriction.setLengthRestriction(lengthRestriction);
+        } else {
+            type.setDataTypeExtendedInfo(lengthRestriction);
+        }
+
+        listener.getParsedDataStack().push(lengthRestriction);
+    }
+
+    /**
+     * Performs validation and updates the data model tree.
+     * It is called when parser exits from grammar rule (length).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processLengthRestrictionExit(TreeWalkListener listener,
+                                                    GeneratedYangParser.LengthStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LENGTH_DATA, ctx.length().getText(), EXIT);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangRangeRestriction) {
+            listener.getParsedDataStack().pop();
+        } else if (tmpData instanceof YangType
+                && ((YangType) tmpData).getDataType() == DERIVED) {
+            // TODO : need to handle in linker
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, LENGTH_DATA,
+                    ctx.length().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ListListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ListListener.java
new file mode 100644
index 0000000..ab91675
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ListListener.java
@@ -0,0 +1,212 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONFIG_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DATA_DEF_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.KEY_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.LIST_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MAX_ELEMENT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MIN_ELEMENT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.validateUniqueInList;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityNonZero;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangListNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  list-stmt           = list-keyword sep identifier-arg-str optsep
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [when-stmt stmtsep]
+ *                            *(if-feature-stmt stmtsep)
+ *                            *(must-stmt stmtsep)
+ *                            [key-stmt stmtsep]
+ *                            *(unique-stmt stmtsep)
+ *                            [config-stmt stmtsep]
+ *                            [min-elements-stmt stmtsep]
+ *                            [max-elements-stmt stmtsep]
+ *                            [ordered-by-stmt stmtsep]
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                            *((typedef-stmt /
+ *                               grouping-stmt) stmtsep)
+ *                            1*(data-def-stmt stmtsep)
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ *  listStatement : LIST_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | mustStatement |
+ *  keyStatement | uniqueStatement | configStatement | minElementsStatement | maxElementsStatement |
+ *  orderedByStatement | statusStatement | descriptionStatement | referenceStatement | typedefStatement |
+ *  groupingStatement| dataDefStatement)* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "list" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ListListener {
+
+    /**
+     * Creates a new list listener.
+     */
+    private ListListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (list), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processListEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.ListStatementContext ctx) {
+
+        YangNode curNode;
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LIST_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), LIST_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, LIST_DATA);
+
+        YangList yangList = getYangListNode(JAVA_GENERATION);
+        yangList.setName(identifier);
+        yangList.setLineNumber(line);
+        yangList.setCharPosition(charPositionInLine);
+        yangList.setFileName(listener.getFileName());
+        /*
+         * If "config" is not specified, the default is the same as the parent
+         * schema node's "config" value.
+         */
+        if (ctx.configStatement().isEmpty()) {
+            boolean parentConfig = ListenerValidation.getParentNodeConfig(listener);
+            yangList.setConfig(parentConfig);
+        }
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangContainer
+                || curData instanceof YangList || curData instanceof YangCase
+                || curData instanceof YangNotification || curData instanceof YangInput
+                || curData instanceof YangOutput || curData instanceof YangAugment
+                || curData instanceof YangGrouping || curData instanceof YangSubModule) {
+            curNode = (YangNode) curData;
+            try {
+                curNode.addChild(yangList);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        LIST_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(yangList);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, LIST_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (list), it performs
+     * validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processListExit(TreeWalkListener listener,
+                                       GeneratedYangParser.ListStatementContext ctx) {
+
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, LIST_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangList) {
+            YangList yangList = (YangList) listener.getParsedDataStack().peek();
+            try {
+                yangList.validateDataOnExit();
+                validateUniqueInList(yangList, ctx);
+            } catch (DataModelException e) {
+                ParserException parserException = new ParserException(constructExtendedListenerErrorMessage(
+                        UNHANDLED_PARSED_DATA, LIST_DATA, ctx.identifier().getText(), EXIT, e.getMessage()));
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, LIST_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of list sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.ListStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.keyStatement(), KEY_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.configStatement(), CONFIG_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.maxElementsStatement(), MAX_ELEMENT_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.minElementsStatement(), MIN_ELEMENT_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, LIST_DATA, ctx.identifier().getText());
+        validateCardinalityNonZero(ctx.dataDefStatement(), DATA_DEF_DATA, LIST_DATA, ctx.identifier().getText(), ctx);
+        //TODO when, typedef, grouping, unique
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java
new file mode 100644
index 0000000..b945f81
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java
@@ -0,0 +1,90 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MANDATORY_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidBooleanValue;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  mandatory-stmt      = mandatory-keyword sep
+ *                        mandatory-arg-str stmtend
+ *
+ *  mandatory-arg-str   = < a string that matches the rule
+ *                          mandatory-arg >
+ *
+ *  mandatory-arg       = true-keyword / false-keyword
+ *
+ * ANTLR grammar rule
+ *  mandatoryStatement : MANDATORY_KEYWORD mandatory STMTEND;
+ *  mandatory          : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "mandatory"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class MandatoryListener {
+
+    /**
+     * Creates a new mandatory listener.
+     */
+    private MandatoryListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (mandatory), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processMandatoryEntry(TreeWalkListener listener,
+                                          GeneratedYangParser.MandatoryStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MANDATORY_DATA, "", ENTRY);
+
+        boolean isMandatory = getValidBooleanValue(ctx.mandatory().getText(), MANDATORY_DATA, ctx);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case LEAF_DATA:
+                YangLeaf leaf = (YangLeaf) tmpNode;
+                leaf.setMandatory(isMandatory);
+                break;
+            case CHOICE_DATA: // TODO
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MANDATORY_DATA, "", ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
new file mode 100644
index 0000000..2f06387
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
@@ -0,0 +1,143 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangMaxElement;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MAX_ELEMENT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  max-elements-stmt   = max-elements-keyword sep
+ *                        max-value-arg-str stmtend
+ *  max-value-arg-str   = < a string that matches the rule
+ *                          max-value-arg >
+ *
+ * ANTLR grammar rule
+ * maxElementsStatement : MAX_ELEMENTS_KEYWORD maxValue STMTEND;
+ * maxValue             : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "max-elements" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class MaxElementsListener {
+
+    private static final String POSITIVE_INTEGER_PATTERN = "[1-9][0-9]*";
+    private static final String UNBOUNDED_KEYWORD = "unbounded";
+
+    /**
+     * Creates a new max-elements listener.
+     */
+    private MaxElementsListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (max-elements), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processMaxElementsEntry(TreeWalkListener listener,
+                                               GeneratedYangParser.MaxElementsStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MAX_ELEMENT_DATA, "", ENTRY);
+
+        int maxElementsValue = getValidMaxElementValue(ctx);
+
+        YangMaxElement maxElement = new YangMaxElement();
+        maxElement.setMaxElement(maxElementsValue);
+
+        maxElement.setLineNumber(ctx.getStart().getLine());
+        maxElement.setCharPosition(ctx.getStart().getCharPositionInLine());
+        maxElement.setFileName(listener.getFileName());
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setMaxElements(maxElement);
+                break;
+            case LIST_DATA:
+                YangList yangList = (YangList) tmpData;
+                yangList.setMaxElements(maxElement);
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MAX_ELEMENT_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * Validates max element value and returns the value from context.
+     *
+     * @param ctx context object of the grammar rule
+     * @return max element's value
+     */
+    private static int getValidMaxElementValue(GeneratedYangParser.MaxElementsStatementContext ctx) {
+
+        int maxElementsValue;
+
+        String value = removeQuotesAndHandleConcat(ctx.maxValue().getText());
+        if (value.equals(UNBOUNDED_KEYWORD)) {
+            maxElementsValue = Integer.MAX_VALUE;
+        } else if (value.matches(POSITIVE_INTEGER_PATTERN)) {
+            try {
+                maxElementsValue = Integer.parseInt(value);
+            } catch (NumberFormatException e) {
+                ParserException parserException = new ParserException("YANG file error : " +
+                                                                              YangConstructType.getYangConstructType(
+                                                                                      MAX_ELEMENT_DATA) + " value " +
+                                                                              value + " is not " +
+                                                                              "valid.");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          YangConstructType.getYangConstructType(
+                                                                                  MAX_ELEMENT_DATA) + " value " +
+                                                                          value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        return maxElementsValue;
+    }
+
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java
new file mode 100644
index 0000000..27cd100
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java
@@ -0,0 +1,101 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangMinElement;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MIN_ELEMENT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNonNegativeIntegerValue;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  min-elements-stmt   = min-elements-keyword sep
+ *                        min-value-arg-str stmtend
+ *  min-value-arg-str   = < a string that matches the rule
+ *                          min-value-arg >
+ *  min-value-arg       = non-negative-integer-value
+ *
+ * ANTLR grammar rule
+ * minElementsStatement : MIN_ELEMENTS_KEYWORD minValue STMTEND;
+ * minValue             : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "min-elements"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class MinElementsListener {
+
+    /**
+     * Creates a new min-elements listener.
+     */
+    private MinElementsListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (min-elements), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processMinElementsEntry(TreeWalkListener listener,
+                                               GeneratedYangParser.MinElementsStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MIN_ELEMENT_DATA, ctx.minValue().getText(), ENTRY);
+
+        int minElementValue = getValidNonNegativeIntegerValue(ctx.minValue().getText(), MIN_ELEMENT_DATA, ctx);
+
+        YangMinElement minElement = new YangMinElement();
+
+        minElement.setMinElement(minElementValue);
+        minElement.setLineNumber(ctx.getStart().getLine());
+        minElement.setCharPosition(ctx.getStart().getCharPositionInLine());
+        minElement.setFileName(listener.getFileName());
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setMinElements(minElement);
+                break;
+            case LIST_DATA:
+                YangList yangList = (YangList) tmpData;
+                yangList.setMinElements(minElement);
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MIN_ELEMENT_DATA,
+                                                                        ctx.minValue().getText(), ENTRY));
+        }
+    }
+
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java
new file mode 100644
index 0000000..02389a1
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ModuleListener.java
@@ -0,0 +1,148 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.ResolvableType;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangReferenceResolver;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.exceptions.LinkerException;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MODULE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CHILD;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangModuleNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * module-stmt         = optsep module-keyword sep identifier-arg-str
+ *                       optsep
+ *                       "{" stmtsep
+ *                           module-header-stmts
+ *                           linkage-stmts
+ *                           meta-stmts
+ *                           revision-stmts
+ *                           body-stmts
+ *                       "}" optsep
+ *
+ * ANTLR grammar rule
+ * module_stmt : MODULE_KEYWORD identifier LEFT_CURLY_BRACE module_body* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "module"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ModuleListener {
+
+    /**
+     * Creates a new module listener.
+     */
+    private ModuleListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (module), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processModuleEntry(TreeWalkListener listener, GeneratedYangParser.ModuleStatementContext ctx) {
+
+        // Check if stack is empty.
+        checkStackIsEmpty(listener, INVALID_HOLDER, MODULE_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), MODULE_DATA, ctx);
+
+        YangModule yangModule = getYangModuleNode(JAVA_GENERATION);
+        yangModule.setName(identifier);
+        yangModule.setLineNumber(ctx.getStart().getLine());
+        yangModule.setCharPosition(ctx.getStart().getCharPositionInLine());
+        yangModule.setFileName(listener.getFileName());
+
+        if (ctx.moduleBody().moduleHeaderStatement().yangVersionStatement() == null) {
+            yangModule.setVersion((byte) 1);
+        }
+
+        listener.getParsedDataStack().push(yangModule);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (module), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processModuleExit(TreeWalkListener listener, GeneratedYangParser.ModuleStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MODULE_DATA, ctx.identifier().getText(), EXIT);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (!(tmpNode instanceof YangModule)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, MODULE_DATA,
+                                                                    ctx.identifier().getText(), EXIT));
+        }
+
+        YangModule module = (YangModule) tmpNode;
+        if (module.getUnresolvedResolutionList(ResolvableType.YANG_COMPILER_ANNOTATION) != null
+                && module.getUnresolvedResolutionList(ResolvableType.YANG_COMPILER_ANNOTATION).size() != 0
+                && module.getChild() != null) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CHILD, MODULE_DATA,
+                                                                    ctx.identifier().getText(), EXIT));
+        }
+
+        try {
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_IF_FEATURE);
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_USES);
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_DERIVED_DATA_TYPE);
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_LEAFREF);
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_BASE);
+            ((YangReferenceResolver) listener.getParsedDataStack()
+                    .peek()).resolveSelfFileLinking(ResolvableType.YANG_IDENTITYREF);
+        } catch (DataModelException e) {
+            LinkerException linkerException = new LinkerException(e.getMessage());
+            linkerException.setLine(e.getLineNumber());
+            linkerException.setCharPosition(e.getCharPositionInLine());
+            linkerException.setFileName(listener.getFileName());
+            throw linkerException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MustListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MustListener.java
new file mode 100644
index 0000000..421ede1
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MustListener.java
@@ -0,0 +1,123 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangMust;
+import org.onosproject.yangutils.datamodel.YangMustHolder;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MUST_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ *  must-stmt           = must-keyword sep string optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [error-message-stmt stmtsep]
+ *                             [error-app-tag-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ * mustStatement : MUST_KEYWORD string (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "must" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class MustListener {
+
+    /**
+     * Creates a new must listener.
+     */
+    private MustListener() {
+    }
+
+    /**
+     * Perform validations and updates the data model tree.It is called when parser
+     * receives an input matching the grammar rule (must).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processMustEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.MustStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MUST_DATA, ctx.string().getText(), ENTRY);
+        String constraint = removeQuotesAndHandleConcat(ctx.string().getText());
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangMustHolder) {
+
+            YangMust must = new YangMust();
+            must.setConstraint(constraint);
+
+            must.setLineNumber(ctx.getStart().getLine());
+            must.setCharPosition(ctx.getStart().getCharPositionInLine());
+            must.setFileName(listener.getFileName());
+            YangMustHolder mustHolder = (YangMustHolder) tmpNode;
+            mustHolder.addMust(must);
+
+            listener.getParsedDataStack().push(must);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MUST_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+
+    }
+
+    /**
+     * Performs validation and updates the data model tree.It is called when parser
+     * exits from grammar rule (must).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processMustExit(TreeWalkListener listener,
+                                       GeneratedYangParser.MustStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MUST_DATA, ctx.string().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangMust) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, MUST_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java
new file mode 100644
index 0000000..6bfaf50
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NamespaceListener.java
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.net.URI;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.NAMESPACE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * module-header-stmts = ;; these stmts can appear in any order
+ *                       [yang-version-stmt stmtsep]
+ *                        namespace-stmt stmtsep
+ *                        prefix-stmt stmtsep
+ *
+ * namespace-stmt      = namespace-keyword sep uri-str optsep stmtend
+ *
+ * ANTLR grammar rule
+ * module_header_statement : yang_version_stmt? namespace_stmt prefix_stmt
+ *                         | yang_version_stmt? prefix_stmt namespace_stmt
+ *                         | namespace_stmt yang_version_stmt? prefix_stmt
+ *                         | namespace_stmt prefix_stmt yang_version_stmt?
+ *                         | prefix_stmt namespace_stmt yang_version_stmt?
+ *                         | prefix_stmt yang_version_stmt? namespace_stmt
+ *                         ;
+ * namespace_stmt : NAMESPACE_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "namespace"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class NamespaceListener {
+
+    /**
+     * Creates a new namespace listener.
+     */
+    private NamespaceListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (namespace), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processNamespaceEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.NamespaceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, NAMESPACE_DATA, ctx.string().getText(), ENTRY);
+
+        if (!validateUriValue(ctx.string().getText())) {
+            ParserException parserException = new ParserException("YANG file error: Invalid namespace URI");
+            parserException.setLine(ctx.string().STRING(0).getSymbol().getLine());
+            parserException.setCharPosition(ctx.string().STRING(0).getSymbol().getCharPositionInLine());
+            throw parserException;
+        }
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case MODULE_DATA: {
+                YangModule module = (YangModule) tmpNode;
+                module.setModuleNamespace(removeQuotesAndHandleConcat(ctx.string().getText()));
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, NAMESPACE_DATA,
+                        ctx.string().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Validate input URI.
+     *
+     * @param uri input namespace URI
+     * @return validation result
+     */
+    private static boolean validateUriValue(String uri) {
+        uri = uri.replace("\"", "");
+        try {
+            URI.create(uri);
+        } catch (Exception e1) {
+            return false;
+        }
+        return true;
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java
new file mode 100644
index 0000000..6109518
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java
@@ -0,0 +1,173 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.RpcNotificationContainer;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.NOTIFICATION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangNotificationNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  notification-stmt   = notification-keyword sep
+ *                        identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             *(if-feature-stmt stmtsep)
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                             *((typedef-stmt /
+ *                                grouping-stmt) stmtsep)
+ *                             *(data-def-stmt stmtsep)
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ *    notificationStatement : NOTIFICATION_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (ifFeatureStatement
+ *                          | statusStatement | descriptionStatement | referenceStatement | typedefStatement
+ *                          | groupingStatement | dataDefStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "notification"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class NotificationListener {
+
+    /**
+     * Creates a new notification listener.
+     */
+    private NotificationListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (notification), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processNotificationEntry(TreeWalkListener listener,
+                                                GeneratedYangParser.NotificationStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, NOTIFICATION_DATA,
+                             ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(),
+                                               NOTIFICATION_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier,
+                                 NOTIFICATION_DATA);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangSubModule) {
+
+            YangNotification notification = getYangNotificationNode(JAVA_GENERATION);
+            notification.setName(identifier);
+
+            notification.setLineNumber(ctx.getStart().getLine());
+            notification.setCharPosition(ctx.getStart().getCharPositionInLine());
+            notification.setFileName(listener.getFileName());
+            ((RpcNotificationContainer) curData).setNotificationPresenceFlag(true);
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(notification);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        NOTIFICATION_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(notification);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, NOTIFICATION_DATA,
+                                                                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (notification), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processNotificationExit(TreeWalkListener listener,
+                                               GeneratedYangParser.NotificationStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, NOTIFICATION_DATA,
+                             ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangNotification) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, NOTIFICATION_DATA,
+                                                                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of notification sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.NotificationStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA,
+                                  NOTIFICATION_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(),
+                                  DESCRIPTION_DATA, NOTIFICATION_DATA,
+                                  ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA,
+                                  NOTIFICATION_DATA,
+                                  ctx.identifier().getText());
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java
new file mode 100644
index 0000000..20a42c1
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OrganizationListener.java
@@ -0,0 +1,119 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.ORGANIZATION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * meta-stmts          = ;; these stmts can appear in any order
+ *                       [organization-stmt stmtsep]
+ *                       [contact-stmt stmtsep]
+ *                       [description-stmt stmtsep]
+ *                       [reference-stmt stmtsep]
+ * organization-stmt   = organization-keyword sep string
+ *                            optsep stmtend
+ *
+ * ANTLR grammar rule
+ * meta_stmts : organization_stmt? contact_stmt? description_stmt? reference_stmt?
+ *            | organization_stmt? contact_stmt? reference_stmt? description_stmt?
+ *            | organization_stmt? description_stmt? contact_stmt? reference_stmt?
+ *            | organization_stmt? description_stmt? reference_stmt? contact_stmt?
+ *            | organization_stmt? reference_stmt? contact_stmt? description_stmt?
+ *            | organization_stmt? reference_stmt? description_stmt? contact_stmt?
+ *            | contact_stmt? organization_stmt? description_stmt? reference_stmt?
+ *            | contact_stmt? organization_stmt? reference_stmt? description_stmt?
+ *            | contact_stmt? reference_stmt? organization_stmt? description_stmt?
+ *            | contact_stmt? reference_stmt? description_stmt? organization_stmt?
+ *            | contact_stmt? description_stmt? reference_stmt? organization_stmt?
+ *            | contact_stmt? description_stmt? organization_stmt? reference_stmt?
+ *            | reference_stmt? contact_stmt? organization_stmt? description_stmt?
+ *            | reference_stmt? contact_stmt? description_stmt? organization_stmt?
+ *            | reference_stmt? organization_stmt? contact_stmt? description_stmt?
+ *            | reference_stmt? organization_stmt? description_stmt? contact_stmt?
+ *            | reference_stmt? description_stmt? organization_stmt? contact_stmt?
+ *            | reference_stmt? description_stmt? contact_stmt? organization_stmt?
+ *            | description_stmt? reference_stmt? contact_stmt? organization_stmt?
+ *            | description_stmt? reference_stmt? organization_stmt? contact_stmt?
+ *            | description_stmt? contact_stmt? reference_stmt? organization_stmt?
+ *            | description_stmt? contact_stmt? organization_stmt? reference_stmt?
+ *            | description_stmt? organization_stmt? contact_stmt? reference_stmt?
+ *            | description_stmt? organization_stmt? reference_stmt? contact_stmt?
+ *            ;
+ * organization_stmt : ORGANIZATION_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "organization" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class OrganizationListener {
+
+    /**
+     * Creates a new organization listener.
+     */
+    private OrganizationListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (organization), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processOrganizationEntry(TreeWalkListener listener,
+                                                GeneratedYangParser.OrganizationStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, ORGANIZATION_DATA, ctx.string().getText(),
+                             ENTRY);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case MODULE_DATA: {
+                YangModule module = (YangModule) tmpNode;
+                module.setOrganization(ctx.string().getText());
+                break;
+            }
+            case SUB_MODULE_DATA: {
+                YangSubModule subModule = (YangSubModule) tmpNode;
+                subModule.setOrganization(ctx.string().getText());
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ORGANIZATION_DATA,
+                        ctx.string().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OutputListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OutputListener.java
new file mode 100644
index 0000000..6ae74b8
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/OutputListener.java
@@ -0,0 +1,131 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.OUTPUT_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangOutputNode;
+import static org.onosproject.yangutils.utils.UtilConstants.OUTPUT;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ *  output-stmt         = output-keyword optsep
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            *((typedef-stmt /
+ *                               grouping-stmt) stmtsep)
+ *                            1*(data-def-stmt stmtsep)
+ *                        "}"
+ *
+ *  outputStatement : OUTPUT_KEYWORD LEFT_CURLY_BRACE outputStatementBody RIGHT_CURLY_BRACE;
+
+ *  outputStatementBody : typedefStatement* dataDefStatement+
+ *                      | dataDefStatement+ typedefStatement*
+ *                      | groupingStatement* dataDefStatement+
+ *                      | dataDefStatement+ groupingStatement*;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "output"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class OutputListener {
+
+    /**
+     * Creates a new output listener.
+     */
+    private OutputListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (output), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processOutputEntry(TreeWalkListener listener,
+                                          GeneratedYangParser.OutputStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, OUTPUT_DATA, "", ENTRY);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangRpc) {
+
+            YangOutput yangOutput = getYangOutputNode(JAVA_GENERATION);
+            yangOutput.setName(OUTPUT);
+            yangOutput.setLineNumber(ctx.getStart().getLine());
+            yangOutput.setCharPosition(ctx.getStart().getCharPositionInLine());
+            yangOutput.setFileName(listener.getFileName());
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(yangOutput);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        OUTPUT_DATA, "", ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(yangOutput);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, OUTPUT_DATA,
+                    "", ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (output), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processOutputExit(TreeWalkListener listener,
+                                         GeneratedYangParser.OutputStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, OUTPUT_DATA, "", EXIT);
+
+        if (!(listener.getParsedDataStack().peek() instanceof YangOutput)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, OUTPUT_DATA,
+                    "", EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PathListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PathListener.java
new file mode 100644
index 0000000..b02c6f4
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PathListener.java
@@ -0,0 +1,89 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeafRef;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.validatePathArgument;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.PATH_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  leafref-specification =
+ *                        ;; these stmts can appear in any order
+ *                        path-stmt stmtsep
+ *                        [require-instance-stmt stmtsep]
+ *
+ * path-stmt           = path-keyword sep path-arg-str stmtend
+ *
+ * ANTLR grammar rule
+ *
+ * leafrefSpecification : (pathStatement (requireInstanceStatement)?) | ((requireInstanceStatement)? pathStatement);
+ *
+ * pathStatement : PATH_KEYWORD path STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "path" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class PathListener {
+
+    /**
+     * Creates a new path listener.
+     */
+    private PathListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (path), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processPathEntry(TreeWalkListener listener,
+            GeneratedYangParser.PathStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PATH_DATA, ctx.path().getText(), ENTRY);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        // Checks the holder of path as leafref, else throws error.
+        if (curData instanceof YangLeafRef) {
+
+            // Splitting the path argument and updating it in the datamodel tree.
+            validatePathArgument(ctx.path().getText(), PATH_DATA, ctx, (YangLeafRef) curData);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, PATH_DATA,
+                    ctx.path().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PatternRestrictionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PatternRestrictionListener.java
new file mode 100644
index 0000000..0d6d1f4
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PatternRestrictionListener.java
@@ -0,0 +1,191 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.util.regex.Pattern;
+import java.util.regex.PatternSyntaxException;
+import org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes;
+import org.onosproject.yangutils.datamodel.YangDerivedInfo;
+import org.onosproject.yangutils.datamodel.YangPatternRestriction;
+import org.onosproject.yangutils.datamodel.YangStringRestriction;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.DERIVED;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.PATTERN_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  pattern-stmt        = pattern-keyword sep string optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [error-message-stmt stmtsep]
+ *                             [error-app-tag-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ *  patternStatement : PATTERN_KEYWORD string (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "pattern"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class PatternRestrictionListener {
+
+    private static final String EMPTY_STRING = "";
+
+    /**
+     * Creates a new pattern restriction listener.
+     */
+    private PatternRestrictionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (pattern), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processPatternRestrictionEntry(TreeWalkListener listener,
+                                                      GeneratedYangParser.PatternStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PATTERN_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData.getYangConstructType() == TYPE_DATA) {
+            YangType type = (YangType) tmpData;
+            setPatternRestriction(listener, type, ctx);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, PATTERN_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Sets the pattern restriction to type.
+     *
+     * @param listener listener's object
+     * @param type     Yang type for which pattern restriction to be set
+     * @param ctx      context object of the grammar rule
+     */
+    private static void setPatternRestriction(TreeWalkListener listener, YangType type,
+                                              GeneratedYangParser.PatternStatementContext ctx) {
+
+        if (type.getDataType() != YangDataTypes.STRING && type.getDataType() != YangDataTypes.DERIVED) {
+
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(PATTERN_DATA) + " name " + ctx.string().getText() +
+                    " can be used to restrict the built-in type string or types derived from string.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        // Validate and get valid pattern restriction string.
+        String patternArgument = getValidPattern(ctx);
+
+        if (type.getDataType() == YangDataTypes.STRING) {
+            YangStringRestriction stringRestriction = (YangStringRestriction) type.getDataTypeExtendedInfo();
+            if (stringRestriction == null) {
+                stringRestriction = new YangStringRestriction();
+                type.setDataTypeExtendedInfo(stringRestriction);
+                stringRestriction.addPattern(patternArgument);
+            } else {
+                stringRestriction.addPattern(patternArgument);
+            }
+            listener.getParsedDataStack().push(stringRestriction);
+        } else {
+            YangPatternRestriction patternRestriction = (YangPatternRestriction) ((YangDerivedInfo<?>) type
+                    .getDataTypeExtendedInfo()).getPatternRestriction();
+            if (patternRestriction == null) {
+                patternRestriction = new YangPatternRestriction();
+                ((YangDerivedInfo<?>) type.getDataTypeExtendedInfo()).setPatternRestriction(patternRestriction);
+                patternRestriction.addPattern(patternArgument);
+            } else {
+                ((YangDerivedInfo<?>) type.getDataTypeExtendedInfo()).setPatternRestriction(patternRestriction);
+                patternRestriction.addPattern(patternArgument);
+            }
+        }
+    }
+
+    /**
+     * Performs validation and updates the data model tree.
+     * It is called when parser exits from grammar rule (pattern).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processPatternRestrictionExit(TreeWalkListener listener,
+                                                    GeneratedYangParser.PatternStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PATTERN_DATA, ctx.string().getText(), EXIT);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangStringRestriction) {
+            listener.getParsedDataStack().pop();
+        } else if (tmpData instanceof YangType
+                && ((YangType) tmpData).getDataType() == DERIVED) {
+            // TODO : need to handle in linker
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, PATTERN_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates and return the valid pattern.
+     *
+     * @param ctx context object of the grammar rule
+     * @return validated string
+     */
+    private static String getValidPattern(GeneratedYangParser.PatternStatementContext ctx) {
+        String userInputPattern = ctx.string().getText().replace("\"", EMPTY_STRING);
+        try {
+            Pattern.compile(userInputPattern);
+        } catch (PatternSyntaxException exception) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(PATTERN_DATA) + " name " + ctx.string().getText() +
+                    " is not a valid regular expression");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        return userInputPattern;
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java
new file mode 100644
index 0000000..3a14927
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java
@@ -0,0 +1,128 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * position-stmt       = position-keyword sep
+ *                       position-value-arg-str stmtend
+ * position-value-arg-str = < a string that matches the rule
+ *                            position-value-arg >
+ * position-value-arg  = non-negative-integer-value
+ * non-negative-integer-value = "0" / positive-integer-value
+ * positive-integer-value = (non-zero-digit *DIGIT)
+ * zero-integer-value  = 1*DIGIT
+ *
+ * ANTLR grammar rule
+ * positionStatement : POSITION_KEYWORD position STMTEND;
+ * position          : string;
+ */
+
+import org.onosproject.yangutils.datamodel.YangBit;
+import org.onosproject.yangutils.datamodel.YangBits;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.POSITION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNonNegativeIntegerValue;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/**
+ * Represents listener based call back function corresponding to the "position"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class PositionListener {
+
+    /**
+     * Creates a new position listener.
+     */
+    private PositionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (position), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processPositionEntry(TreeWalkListener listener,
+            GeneratedYangParser.PositionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case BIT_DATA: {
+                YangBit bitNode = (YangBit) tmpNode;
+                int positionValue = getValidBitPosition(listener, ctx);
+                bitNode.setPosition(positionValue);
+                break;
+            }
+            default:
+                throw new ParserException(
+                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Validates BITS position value correctness and uniqueness.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     * @return position value
+     */
+    private static int getValidBitPosition(TreeWalkListener listener,
+            GeneratedYangParser.PositionStatementContext ctx) {
+        Parsable bitNode = listener.getParsedDataStack().pop();
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY);
+
+        int positionValue = getValidNonNegativeIntegerValue(ctx.position().getText(), POSITION_DATA, ctx);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case BITS_DATA: {
+                YangBits yangBits = (YangBits) tmpNode;
+                listener.getParsedDataStack().push(bitNode);
+                if (yangBits.isBitPositionExists(positionValue)) {
+                    ParserException parserException = new ParserException("YANG file error: Duplicate value of " +
+                                                                                  "position is invalid.");
+                    parserException.setLine(ctx.getStart().getLine());
+                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                    throw parserException;
+                }
+                return positionValue;
+            }
+            default:
+                listener.getParsedDataStack().push(bitNode);
+                throw new ParserException(
+                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java
new file mode 100644
index 0000000..b75f77c
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PrefixListener.java
@@ -0,0 +1,107 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangBelongsTo;
+import org.onosproject.yangutils.datamodel.YangImport;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.PREFIX_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * module-header-stmts = ;; these stmts can appear in any order
+ *                       [yang-version-stmt stmtsep]
+ *                        namespace-stmt stmtsep
+ *                        prefix-stmt stmtsep
+ *
+ * prefix-stmt         = prefix-keyword sep prefix-arg-str
+ *                       optsep stmtend
+ *
+ * ANTLR grammar rule
+ * module_header_statement : yang_version_stmt? namespace_stmt prefix_stmt
+ *                         | yang_version_stmt? prefix_stmt namespace_stmt
+ *                         | namespace_stmt yang_version_stmt? prefix_stmt
+ *                         | namespace_stmt prefix_stmt yang_version_stmt?
+ *                         | prefix_stmt namespace_stmt yang_version_stmt?
+ *                         | prefix_stmt yang_version_stmt? namespace_stmt
+ *                         ;
+ * prefix_stmt : PREFIX_KEYWORD identifier STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "prefix"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class PrefixListener {
+
+    /**
+     * Creates a new prefix listener.
+     */
+    private PrefixListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (prefix),perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processPrefixEntry(TreeWalkListener listener, GeneratedYangParser.PrefixStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PREFIX_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), PREFIX_DATA, ctx);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case MODULE_DATA: {
+                YangModule module = (YangModule) tmpNode;
+                module.setPrefix(identifier);
+                break;
+            }
+            case IMPORT_DATA: {
+                YangImport importNode = (YangImport) tmpNode;
+                importNode.setPrefixId(identifier);
+                break;
+            }
+            case BELONGS_TO_DATA: {
+                YangBelongsTo belongstoNode = (YangBelongsTo) tmpNode;
+                belongstoNode.setPrefix(identifier);
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, PREFIX_DATA,
+                        ctx.identifier().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PresenceListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PresenceListener.java
new file mode 100644
index 0000000..ef744d5
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PresenceListener.java
@@ -0,0 +1,78 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CONTAINER_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.PRESENCE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * presence-stmt       = presence-keyword sep string stmtend
+ *
+ * ANTLR grammar rule
+ * presenceStatement : PRESENCE_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "presence"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class PresenceListener {
+
+    /**
+     * Creates a new presence listener.
+     */
+    private PresenceListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (presence), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processPresenceEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.PresenceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, PRESENCE_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData.getYangConstructType() == CONTAINER_DATA) {
+            YangContainer container = (YangContainer) tmpData;
+            container.setPresence(ctx.string().getText());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, PRESENCE_DATA,
+                    ctx.string().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RangeRestrictionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RangeRestrictionListener.java
new file mode 100644
index 0000000..3b4ae43
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RangeRestrictionListener.java
@@ -0,0 +1,180 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangDecimal64;
+import org.onosproject.yangutils.datamodel.YangDerivedInfo;
+import org.onosproject.yangutils.datamodel.YangRangeRestriction;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.DECIMAL64;
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes.DERIVED;
+import static org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypeUtils.isOfRangeRestrictedType;
+import static org.onosproject.yangutils.datamodel.utils.RestrictionResolver.processRangeRestriction;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.RANGE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  range-stmt          = range-keyword sep range-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [error-message-stmt stmtsep]
+ *                             [error-app-tag-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ *  rangeStatement : RANGE_KEYWORD range (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "range"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class RangeRestrictionListener {
+
+    /**
+     * Creates a new range restriction listener.
+     */
+    private RangeRestrictionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (range), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processRangeRestrictionEntry(TreeWalkListener listener,
+                                                    GeneratedYangParser.RangeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, RANGE_DATA, ctx.range().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData.getYangConstructType() == TYPE_DATA) {
+            YangType type = (YangType) tmpData;
+            setRangeRestriction(listener, type, ctx);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, RANGE_DATA,
+                    ctx.range().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Sets the range restriction to type.
+     *
+     * @param listener listener's object
+     * @param type     YANG type for which range restriction to be added
+     * @param ctx      context object of the grammar rule
+     */
+    private static void setRangeRestriction(TreeWalkListener listener, YangType type,
+                                            GeneratedYangParser.RangeStatementContext ctx) {
+
+        if (type.getDataType() == DERIVED) {
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setRangeRestrictionString(ctx.range().getText());
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setLineNumber(ctx.getStart().getLine());
+            ((YangDerivedInfo<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                    .setCharPosition(ctx.getStart().getCharPositionInLine());
+            return;
+        }
+
+        if (!(isOfRangeRestrictedType(type.getDataType())) && (type.getDataType() != DECIMAL64)) {
+            ParserException parserException = new ParserException("YANG file error: Range restriction can't be " +
+                    "applied to a given type");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        YangRangeRestriction rangeRestriction = null;
+        try {
+            if (type.getDataType() == DECIMAL64) {
+                YangDecimal64 yangDecimal64 = (YangDecimal64) type.getDataTypeExtendedInfo();
+                rangeRestriction = processRangeRestriction(yangDecimal64.getDefaultRangeRestriction(),
+                                                           ctx.getStart().getLine(),
+                                                           ctx.getStart().getCharPositionInLine(),
+                                                           true, ctx.range().getText(), type.getDataType());
+            } else {
+                rangeRestriction = processRangeRestriction(null, ctx.getStart().getLine(),
+                                                           ctx.getStart().getCharPositionInLine(),
+                                                           false, ctx.range().getText(), type.getDataType());
+            }
+        } catch (DataModelException e) {
+            ParserException parserException = new ParserException(e.getMessage());
+            parserException.setCharPosition(e.getCharPositionInLine());
+            parserException.setLine(e.getLineNumber());
+            throw parserException;
+        }
+
+        if (rangeRestriction != null) {
+            if (type.getDataType() == DECIMAL64) {
+                ((YangDecimal64<YangRangeRestriction>) type.getDataTypeExtendedInfo())
+                        .setRangeRestrictedExtendedInfo(rangeRestriction);
+            } else {
+                type.setDataTypeExtendedInfo(rangeRestriction);
+            }
+        }
+        listener.getParsedDataStack().push(rangeRestriction);
+    }
+
+    /**
+     * Performs validation and updates the data model tree.
+     * It is called when parser exits from grammar rule (range).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processRangeRestrictionExit(TreeWalkListener listener,
+                                                   GeneratedYangParser.RangeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, RANGE_DATA, ctx.range().getText(), EXIT);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangRangeRestriction) {
+            listener.getParsedDataStack().pop();
+        } else if (tmpData instanceof YangType
+                && ((YangType) tmpData).getDataType() == DERIVED) {
+            // TODO : need to handle in linker
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, RANGE_DATA,
+                    ctx.range().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ReferenceListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ReferenceListener.java
new file mode 100644
index 0000000..02cdf62
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ReferenceListener.java
@@ -0,0 +1,77 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangReference;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * reference-stmt      = reference-keyword sep string optsep stmtend
+ *
+ * ANTLR grammar rule
+ * referenceStatement : REFERENCE_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "reference"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ReferenceListener {
+
+    /**
+     * Creates a new reference listener.
+     */
+    private ReferenceListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (reference), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processReferenceEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.ReferenceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REFERENCE_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangReference) {
+            YangReference reference = (YangReference) tmpData;
+            reference.setReference(ctx.string().getText());
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REFERENCE_DATA,
+                            ctx.string().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RequireInstanceListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RequireInstanceListener.java
new file mode 100644
index 0000000..21c7533
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RequireInstanceListener.java
@@ -0,0 +1,106 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeafRef;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REQUIRE_INSTANCE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidBooleanValue;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * require-instance-stmt = require-instance-keyword sep
+ *                            require-instance-arg-str stmtend
+ *
+ * require-instance-arg-str = < a string that matches the rule
+ *                            require-instance-arg >
+ *
+ * require-instance-arg = true-keyword / false-keyword
+ *
+ * ANTLR grammar rule
+ *
+ * requireInstanceStatement : REQUIRE_INSTANCE_KEYWORD requireInstance STMTEND;
+ *
+ * requireInstance : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "require-instance" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class RequireInstanceListener {
+
+    /**
+     * Creates a new require instance listener.
+     */
+    private RequireInstanceListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (require-instance), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processRequireInstanceEntry(TreeWalkListener listener,
+            GeneratedYangParser.RequireInstanceStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REQUIRE_INSTANCE_DATA, "", ENTRY);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        // Gets the status of require instance
+        boolean isRequireInstance = getValidBooleanValue(ctx.requireInstance().getText(), REQUIRE_INSTANCE_DATA, ctx);
+
+        // Checks the holder of require-instance as leafref or type, else throws error.
+        if (curData instanceof YangLeafRef) {
+
+            // Sets the require-instance status to leafref.
+            ((YangLeafRef) curData).setRequireInstance(isRequireInstance);
+        } else if (curData instanceof YangType) {
+
+            // Checks type should be instance-identifier, else throw error.
+            if (((YangType) curData).getDataType() == YangDataTypes.INSTANCE_IDENTIFIER) {
+
+                // Sets the require-instance status to instance-identifier type.
+                ((YangType) curData).setDataTypeExtendedInfo(isRequireInstance);
+            } else {
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REQUIRE_INSTANCE_DATA,
+                        ctx.getText(), ENTRY));
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REQUIRE_INSTANCE_DATA,
+                    ctx.getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java
new file mode 100644
index 0000000..3ff67fe
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionDateListener.java
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.util.Date;
+import org.onosproject.yangutils.datamodel.YangImport;
+import org.onosproject.yangutils.datamodel.YangInclude;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REVISION_DATE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidDateFromString;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * import-stmt         = import-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           prefix-stmt stmtsep
+ *                           [revision-date-stmt stmtsep]
+ *                        "}"
+ * include-stmt        = include-keyword sep identifier-arg-str optsep
+ *                             (";" /
+ *                              "{" stmtsep
+ *                                  [revision-date-stmt stmtsep]
+ *                            "}")
+ * revision-date-stmt = revision-date-keyword sep revision-date stmtend
+ *
+ * ANTLR grammar rule
+ * import_stmt : IMPORT_KEYWORD IDENTIFIER LEFT_CURLY_BRACE import_stmt_body
+ *               RIGHT_CURLY_BRACE;
+ * import_stmt_body : prefix_stmt revision_date_stmt?;
+ *
+ * include_stmt : INCLUDE_KEYWORD IDENTIFIER (STMTEND | LEFT_CURLY_BRACE
+ *                revision_date_stmt_body? RIGHT_CURLY_BRACE);
+ *
+ * revision_date_stmt : REVISION_DATE_KEYWORD DATE_ARG STMTEND;
+ *
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "revision date" rule defined in ANTLR grammar file for corresponding ABNF
+ * rule in RFC 6020.
+ */
+public final class RevisionDateListener {
+
+    /**
+     * Creates a new revision date listener.
+     */
+    private RevisionDateListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (revision date),perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processRevisionDateEntry(TreeWalkListener listener,
+            GeneratedYangParser.RevisionDateStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATE_DATA, ctx.dateArgumentString().getText(),
+                ENTRY);
+
+        Date date = getValidDateFromString(ctx.dateArgumentString().getText(), ctx);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case IMPORT_DATA: {
+                YangImport importNode = (YangImport) tmpNode;
+                importNode.setRevision(date);
+                break;
+            }
+            case INCLUDE_DATA: {
+                YangInclude includeNode = (YangInclude) tmpNode;
+                includeNode.setRevision(date);
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REVISION_DATE_DATA,
+                        ctx.dateArgumentString().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java
new file mode 100644
index 0000000..cb633b8
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RevisionListener.java
@@ -0,0 +1,169 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import java.util.Date;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangRevision;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REVISION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidDateFromString;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * module-stmt         = optsep module-keyword sep identifier-arg-str
+ *                       optsep
+ *                       "{" stmtsep
+ *                           module-header-stmts
+ *                           linkage-stmts
+ *                           meta-stmts
+ *                           revision-stmts
+ *                           body-stmts
+ *                       "}" optsep
+ *
+ * revision-stmt       = revision-keyword sep revision-date optsep
+ *                             (";" /
+ *                              "{" stmtsep
+ *                                  [description-stmt stmtsep]
+ *                                  [reference-stmt stmtsep]
+ *                              "}")
+ *
+ * ANTLR grammar rule
+ * module_stmt : MODULE_KEYWORD IDENTIFIER LEFT_CURLY_BRACE module_body* RIGHT_CURLY_BRACE;
+ *
+ * revision_stmt : REVISION_KEYWORD DATE_ARG (STMTEND | LEFT_CURLY_BRACE revision_stmt_body RIGHT_CURLY_BRACE);
+ * revision_stmt_body : description_stmt? reference_stmt?;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "revision"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class RevisionListener {
+
+    /**
+     * Creates a new revision listener.
+     */
+    private RevisionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (revision),perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processRevisionEntry(TreeWalkListener listener,
+                                            GeneratedYangParser.RevisionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.dateArgumentString().getText(), ENTRY);
+
+        Date date = getValidDateFromString(ctx.dateArgumentString().getText(), ctx);
+
+        YangRevision revisionNode = new YangRevision();
+        revisionNode.setRevDate(date);
+
+        listener.getParsedDataStack().push(revisionNode);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (revision), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processRevisionExit(TreeWalkListener listener, GeneratedYangParser.RevisionStatementContext
+            ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.dateArgumentString().getText(), EXIT);
+
+        Parsable tmpRevisionNode = listener.getParsedDataStack().peek();
+        if (tmpRevisionNode instanceof YangRevision) {
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, REVISION_DATA, ctx.dateArgumentString().getText(),
+                                 EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case MODULE_DATA: {
+                    YangModule module = (YangModule) tmpNode;
+                    if (module.getRevision() != null) {
+                        Date curRevisionDate = module.getRevision().getRevDate();
+                        if (curRevisionDate.before(((YangRevision) tmpRevisionNode).getRevDate())) {
+                            module.setRevision((YangRevision) tmpRevisionNode);
+                        }
+                    } else {
+                        module.setRevision((YangRevision) tmpRevisionNode);
+                    }
+                    break;
+                }
+                case SUB_MODULE_DATA: {
+                    YangSubModule subModule = (YangSubModule) tmpNode;
+                    if (subModule.getRevision() != null) {
+                        Date curRevisionDate = subModule.getRevision().getRevDate();
+                        if (curRevisionDate.before(((YangRevision) tmpRevisionNode).getRevDate())) {
+                            subModule.setRevision((YangRevision) tmpRevisionNode);
+                        }
+                    } else {
+                        subModule.setRevision((YangRevision) tmpRevisionNode);
+                    }
+                    break;
+                }
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, REVISION_DATA,
+                            ctx.dateArgumentString().getText(),
+                            EXIT));
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, REVISION_DATA,
+                                                                    ctx.dateArgumentString().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validate revision.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     * @return validation result
+     */
+    private static boolean validateRevision(TreeWalkListener listener,
+                                            GeneratedYangParser.RevisionStatementContext ctx) {
+        // TODO to be implemented
+        return true;
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java
new file mode 100644
index 0000000..e037e52
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java
@@ -0,0 +1,166 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.INPUT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.OUTPUT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.RPC_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangRpcNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  rpc-stmt            = rpc-keyword sep identifier-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             *(if-feature-stmt stmtsep)
+ *                             [status-stmt stmtsep]
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                             *((typedef-stmt /
+ *                                grouping-stmt) stmtsep)
+ *                             [input-stmt stmtsep]
+ *                             [output-stmt stmtsep]
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ *  rpcStatement : RPC_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (ifFeatureStatement | statusStatement
+ *               | descriptionStatement | referenceStatement | typedefStatement | groupingStatement | inputStatement
+ *               | outputStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "rpc"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class RpcListener {
+
+    /**
+     * Creates a new rpc listener.
+     */
+    private RpcListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (rpc), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processRpcEntry(TreeWalkListener listener,
+                                       GeneratedYangParser.RpcStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, RPC_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), RPC_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, RPC_DATA);
+
+        Parsable curData = listener.getParsedDataStack().peek();
+        if (curData instanceof YangModule || curData instanceof YangSubModule) {
+
+            YangNode curNode = (YangNode) curData;
+            YangRpc yangRpc = getYangRpcNode(JAVA_GENERATION);
+
+            yangRpc.setLineNumber(ctx.getStart().getLine());
+            yangRpc.setCharPosition(ctx.getStart().getCharPositionInLine());
+            yangRpc.setFileName(listener.getFileName());
+            yangRpc.setName(identifier);
+            try {
+                curNode.addChild(yangRpc);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        RPC_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(yangRpc);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, RPC_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (rpc), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processRpcExit(TreeWalkListener listener,
+                                      GeneratedYangParser.RpcStatementContext ctx) {
+
+        //Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, RPC_DATA, ctx.identifier().getText(), EXIT);
+
+        if (!(listener.getParsedDataStack().peek() instanceof YangRpc)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, RPC_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+        listener.getParsedDataStack().pop();
+    }
+
+    /**
+     * Validates the cardinality of rpc sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.RpcStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, RPC_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, RPC_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, RPC_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.inputStatement(), INPUT_DATA, RPC_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.outputStatement(), OUTPUT_DATA, RPC_DATA, ctx.identifier().getText());
+    }
+
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ShortCaseListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ShortCaseListener.java
new file mode 100644
index 0000000..6963a98
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ShortCaseListener.java
@@ -0,0 +1,149 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangChoice;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.CASE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.SHORT_CASE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CHILD;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangCaseNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * short-case-stmt     = container-stmt /
+ *                       leaf-stmt /
+ *                       leaf-list-stmt /
+ *                       list-stmt /
+ *                       anyxml-stmt
+ *
+ * ANTLR grammar rule
+ * shortCaseStatement : containerStatement | leafStatement | leafListStatement | listStatement;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "short
+ * case" rule defined in ANTLR grammar file for corresponding ABNF rule in RFC
+ * 6020.
+ */
+public final class ShortCaseListener {
+
+    /**
+     * Create a new short case listener.
+     */
+    private ShortCaseListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (short case), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processShortCaseEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.ShortCaseStatementContext ctx) {
+
+        ParseTree errorConstructContext;
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, SHORT_CASE_DATA, "", ENTRY);
+
+        YangCase caseNode = getYangCaseNode(JAVA_GENERATION);
+
+        caseNode.setLineNumber(ctx.getStart().getLine());
+        caseNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+        caseNode.setFileName(listener.getFileName());
+        if (ctx.containerStatement() != null) {
+            caseNode.setName(getValidIdentifier(ctx.containerStatement().identifier().getText(), CASE_DATA, ctx));
+            errorConstructContext = ctx.containerStatement();
+        } else if (ctx.listStatement() != null) {
+            caseNode.setName(getValidIdentifier(ctx.listStatement().identifier().getText(), CASE_DATA, ctx));
+            errorConstructContext = ctx.listStatement();
+        } else if (ctx.leafListStatement() != null) {
+            caseNode.setName(getValidIdentifier(ctx.leafListStatement().identifier().getText(), CASE_DATA, ctx));
+            errorConstructContext = ctx.leafListStatement();
+        } else if (ctx.leafStatement() != null) {
+            caseNode.setName(getValidIdentifier(ctx.leafStatement().identifier().getText(), CASE_DATA, ctx));
+            errorConstructContext = ctx.leafStatement();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CHILD, SHORT_CASE_DATA, "", ENTRY));
+        }
+        // TODO implement for augment.
+
+        int line = ((ParserRuleContext) errorConstructContext).getStart().getLine();
+        int charPositionInLine = ((ParserRuleContext) errorConstructContext).getStart().getCharPositionInLine();
+
+        // Check for identifier collision
+        detectCollidingChildUtil(listener, line, charPositionInLine, caseNode.getName(), CASE_DATA);
+
+        if ((listener.getParsedDataStack().peek()) instanceof YangChoice) {
+            try {
+                ((YangChoice) listener.getParsedDataStack().peek()).addChild(caseNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        SHORT_CASE_DATA, caseNode.getName(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(caseNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, SHORT_CASE_DATA,
+                    caseNode.getName(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (short case), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processShortCaseExit(TreeWalkListener listener,
+                                            GeneratedYangParser.ShortCaseStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, SHORT_CASE_DATA, "", EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangCase) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, SHORT_CASE_DATA,
+                    "", EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java
new file mode 100644
index 0000000..81d6b61
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java
@@ -0,0 +1,127 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangStatus;
+import org.onosproject.yangutils.datamodel.YangStatusType;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  status-stmt         = status-keyword sep status-arg-str stmtend
+ *  status-arg-str      = < a string that matches the rule
+ *                         status-arg >
+ *  status-arg          = current-keyword /
+ *                        obsolete-keyword /
+ *                        deprecated-keyword
+ *
+ * ANTLR grammar rule
+ * statusStatement : STATUS_KEYWORD status STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "status"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class StatusListener {
+
+    private static final String CURRENT_KEYWORD = "current";
+    private static final String DEPRECATED_KEYWORD = "deprecated";
+    private static final String OBSOLETE_KEYWORD = "obsolete";
+
+    /**
+     * Creates a new status listener.
+     */
+    private StatusListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (status), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processStatusEntry(TreeWalkListener listener,
+                                          GeneratedYangParser.StatusStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, STATUS_DATA, "", ENTRY);
+
+        YangStatusType status = getValidStatus(ctx);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (tmpData instanceof YangStatus) {
+            YangStatus yangStatus = (YangStatus) tmpData;
+            yangStatus.setStatus(status);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, STATUS_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * Validates status value and returns the value from context.
+     *
+     * @param ctx context object of the grammar rule
+     * @return status current/deprecated/obsolete
+     */
+    private static YangStatusType getValidStatus(GeneratedYangParser.StatusStatementContext ctx) {
+
+        YangStatusType status;
+
+        String value = removeQuotesAndHandleConcat(ctx.status().getText());
+        switch (value) {
+            case CURRENT_KEYWORD: {
+                status = YangStatusType.CURRENT;
+                break;
+            }
+            case DEPRECATED_KEYWORD: {
+                status = YangStatusType.DEPRECATED;
+                break;
+            }
+            case OBSOLETE_KEYWORD: {
+                status = YangStatusType.OBSOLETE;
+                break;
+            }
+            default: {
+                ParserException parserException = new ParserException("YANG file error : " +
+                        YangConstructType.getYangConstructType(STATUS_DATA) + " " + ctx.status().getText() +
+                        " is not valid.");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+        }
+
+        return status;
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
new file mode 100644
index 0000000..d2c7347
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/SubModuleListener.java
@@ -0,0 +1,154 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.ResolvableType;
+import org.onosproject.yangutils.datamodel.YangReferenceResolver;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.exceptions.LinkerException;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.MODULE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.SUB_MODULE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CHILD;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangSubModuleNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * submodule-stmt      = optsep submodule-keyword sep identifier-arg-str
+ *                             optsep
+ *                             "{" stmtsep
+ *                                 submodule-header-stmts
+ *                                 linkage-stmts
+ *                                 meta-stmts
+ *                                 revision-stmts
+ *                                 body-stmts
+ *                             "}" optsep
+ *
+ * ANTLR grammar rule
+ * submodule_stmt : SUBMODULE_KEYWORD identifier LEFT_CURLY_BRACE submodule_body* RIGHT_CURLY_BRACE;
+ * submodule_body : submodule_header_statement linkage_stmts meta_stmts revision_stmts body_stmts;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "submodule"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class SubModuleListener {
+
+    /**
+     * Creates a new sub module listener.
+     */
+    private SubModuleListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule (sub
+     * module), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processSubModuleEntry(TreeWalkListener listener,
+                                             GeneratedYangParser.SubModuleStatementContext ctx) {
+
+        // Check if stack is empty.
+        checkStackIsEmpty(listener, INVALID_HOLDER, SUB_MODULE_DATA, ctx.identifier().getText(),
+                          ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), SUB_MODULE_DATA, ctx);
+
+        YangSubModule yangSubModule = getYangSubModuleNode(JAVA_GENERATION);
+        yangSubModule.setName(identifier);
+
+        yangSubModule.setLineNumber(ctx.getStart().getLine());
+        yangSubModule.setCharPosition(ctx.getStart().getCharPositionInLine());
+        yangSubModule.setFileName(listener.getFileName());
+        if (ctx.submoduleBody().submoduleHeaderStatement().yangVersionStatement() == null) {
+            yangSubModule.setVersion((byte) 1);
+        }
+
+        listener.getParsedDataStack().push(yangSubModule);
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (submodule), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processSubModuleExit(TreeWalkListener listener,
+                                            GeneratedYangParser.SubModuleStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, SUB_MODULE_DATA, ctx.identifier().getText(),
+                             EXIT);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (!(tmpNode instanceof YangSubModule)) {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, SUB_MODULE_DATA,
+                                                                    ctx.identifier().getText(), EXIT));
+        }
+
+        YangSubModule subModule = (YangSubModule) tmpNode;
+        if (subModule.getUnresolvedResolutionList(ResolvableType.YANG_COMPILER_ANNOTATION) != null
+                && subModule.getUnresolvedResolutionList(ResolvableType.YANG_COMPILER_ANNOTATION).size() != 0
+                && subModule.getChild() != null) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CHILD, MODULE_DATA,
+                                                                    ctx.identifier().getText(), EXIT));
+        }
+
+        try {
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_IF_FEATURE);
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_USES);
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_DERIVED_DATA_TYPE);
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_LEAFREF);
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_BASE);
+            ((YangReferenceResolver) listener.getParsedDataStack().peek())
+                    .resolveSelfFileLinking(ResolvableType.YANG_IDENTITYREF);
+        } catch (DataModelException e) {
+            LinkerException linkerException = new LinkerException(e.getMessage());
+            linkerException.setLine(e.getLineNumber());
+            linkerException.setCharPosition(e.getCharPositionInLine());
+            linkerException.setFileName(listener.getFileName());
+            throw linkerException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
new file mode 100644
index 0000000..4821cfa
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeDefListener.java
@@ -0,0 +1,200 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DEFAULT_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPEDEF_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CONTENT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityEqualsOne;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangTypeDefNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * body-stmts          = *((extension-stmt /
+ *                          feature-stmt /
+ *                          identity-stmt /
+ *                          typedef-stmt /
+ *                          grouping-stmt /
+ *                          data-def-stmt /
+ *                          augment-stmt /
+ *                          rpc-stmt /
+ *                          notification-stmt /
+ *                          deviation-stmt) stmtsep)
+ *
+ * typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
+ *                       "{" stmtsep
+ *                           ;; these stmts can appear in any order
+ *                           type-stmt stmtsep
+ *                          [units-stmt stmtsep]
+ *                           [default-stmt stmtsep]
+ *                           [status-stmt stmtsep]
+ *                           [description-stmt stmtsep]
+ *                           [reference-stmt stmtsep]
+ *                         "}"
+ *
+ * ANTLR grammar rule
+ * typedefStatement : TYPEDEF_KEYWORD identifier LEFT_CURLY_BRACE
+ *                (typeStatement | unitsStatement | defaultStatement | statusStatement
+ *                | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "typedef"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class TypeDefListener {
+
+    /**
+     * Creates a new typedef listener.
+     */
+    private TypeDefListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (typedef), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processTypeDefEntry(TreeWalkListener listener,
+            GeneratedYangParser.TypedefStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, TYPEDEF_DATA, ctx.identifier().getText(), ENTRY);
+
+        String identifier = getValidIdentifier(ctx.identifier().getText(), TYPEDEF_DATA, ctx);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+        detectCollidingChildUtil(listener, line, charPositionInLine, identifier, TYPEDEF_DATA);
+
+        /*
+         * Create a derived type information, the base type must be set in type
+         * listener.
+         */
+        YangTypeDef typeDefNode = getYangTypeDefNode(JAVA_GENERATION);
+        typeDefNode.setName(identifier);
+
+        typeDefNode.setLineNumber(ctx.getStart().getLine());
+        typeDefNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+        typeDefNode.setFileName(listener.getFileName());
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        if (curData instanceof YangModule || curData instanceof YangSubModule || curData instanceof YangContainer
+                || curData instanceof YangList || curData instanceof YangNotification || curData instanceof YangRpc
+                || curData instanceof YangInput || curData instanceof YangOutput || curData instanceof YangGrouping) {
+
+            YangNode curNode = (YangNode) curData;
+            try {
+                curNode.addChild(typeDefNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        TYPEDEF_DATA, ctx.identifier().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(typeDefNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    TYPEDEF_DATA, ctx.identifier().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (typedef), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processTypeDefExit(TreeWalkListener listener,
+            GeneratedYangParser.TypedefStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, TYPEDEF_DATA, ctx.identifier().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangTypeDef) {
+            YangTypeDef typeDefNode = (YangTypeDef) listener.getParsedDataStack().peek();
+            try {
+                typeDefNode.validateDataOnExit();
+            } catch (DataModelException e) {
+                throw new ParserException(constructListenerErrorMessage(INVALID_CONTENT, TYPEDEF_DATA,
+                        ctx.identifier().getText(), EXIT));
+            }
+
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, TYPEDEF_DATA,
+                    ctx.identifier().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Validates the cardinality of typedef sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.TypedefStatementContext ctx) {
+
+        validateCardinalityMaxOne(ctx.unitsStatement(), UNITS_DATA, TYPEDEF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.defaultStatement(), DEFAULT_DATA, TYPEDEF_DATA, ctx.identifier().getText());
+        validateCardinalityEqualsOne(ctx.typeStatement(), TYPE_DATA, TYPEDEF_DATA, ctx.identifier().getText(), ctx);
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, TYPEDEF_DATA,
+                ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, TYPEDEF_DATA, ctx.identifier().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, TYPEDEF_DATA, ctx.identifier().getText());
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeListener.java
new file mode 100644
index 0000000..8ed701e
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/TypeListener.java
@@ -0,0 +1,339 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangDerivedInfo;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.YangUnion;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.builtindatatype.YangDataTypes;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.UNRESOLVED;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPEDEF_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNodeIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangType;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *  type-stmt           = type-keyword sep identifier-ref-arg-str optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                            type-body-stmts
+ *                         "}")
+ *
+ * ANTLR grammar rule
+ * typeStatement : TYPE_KEYWORD string (STMTEND | LEFT_CURLY_BRACE typeBodyStatements RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "type" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class TypeListener {
+
+    /**
+     * Creates a new type listener.
+     */
+    private TypeListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (type), performs validation and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processTypeEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.TypeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, TYPE_DATA, ctx.string().getText(), ENTRY);
+
+        // Validate node identifier.
+        YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(ctx.string().getText(), TYPE_DATA,
+                ctx);
+
+        // Obtain the YANG data type.
+        YangDataTypes yangDataTypes = YangDataTypes.getType(ctx.string().getText());
+
+        // validate type sub-statement cardinality
+        validateTypeSubStatementCardinality(ctx, yangDataTypes);
+
+        // Create YANG type object and fill the values.
+        YangType<?> type = getYangType(JAVA_GENERATION);
+        type.setNodeIdentifier(nodeIdentifier);
+        type.setDataType(yangDataTypes);
+
+        type.setLineNumber(ctx.getStart().getLine());
+        type.setCharPosition(ctx.getStart().getCharPositionInLine());
+        type.setFileName(listener.getFileName());
+        // Set default require instance value as true for instance identifier.
+        setDefaultRequireInstanceForInstanceIdentifier(type);
+
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_DATA:
+                YangLeaf leaf = (YangLeaf) tmpData;
+                leaf.setDataType(type);
+
+                /*
+                 * If data type is derived, resolution information to be added
+                 * in resolution list.
+                 */
+                if (yangDataTypes == YangDataTypes.DERIVED) {
+                    // Parent YANG node of leaf to be added in resolution information.
+                    Parsable leafData = listener.getParsedDataStack().pop();
+                    Parsable parentNodeOfLeaf = listener.getParsedDataStack().peek();
+                    listener.getParsedDataStack().push(leafData);
+
+                    // Verify parent node of leaf
+                    if (!(parentNodeOfLeaf instanceof YangNode)) {
+                        throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                                ctx.string().getText(), EXIT));
+                    }
+
+                    // Create empty derived info and attach it to type extended info.
+                    YangDerivedInfo<?> yangDerivedInfo = new YangDerivedInfo<>();
+                    ((YangType<YangDerivedInfo>) type).setDataTypeExtendedInfo(yangDerivedInfo);
+
+                    type.setResolvableStatus(UNRESOLVED);
+
+                    // Add resolution information to the list
+                    YangResolutionInfoImpl resolutionInfo =
+                            new YangResolutionInfoImpl<YangType>(
+                                    type,(YangNode) parentNodeOfLeaf, errorLine,
+                                    errorPosition);
+                    addToResolutionList(resolutionInfo, ctx);
+                }
+                break;
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setDataType(type);
+
+                /*
+                 * If data type is derived, resolution information to be added
+                 * in resolution list.
+                 */
+                if (yangDataTypes == YangDataTypes.DERIVED) {
+                    // Parent YANG node of leaf list to be added in resolution information.
+                    Parsable leafListData = listener.getParsedDataStack().pop();
+                    Parsable parentNodeOfLeafList = listener.getParsedDataStack().peek();
+                    listener.getParsedDataStack().push(leafListData);
+
+                    // Verify parent node of leaf
+                    if (!(parentNodeOfLeafList instanceof YangNode)) {
+                        throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                                ctx.string().getText(), EXIT));
+                    }
+
+                    // Create empty derived info and attach it to type extended info.
+                    YangDerivedInfo<?> yangDerivedInfo = new YangDerivedInfo<>();
+                    ((YangType<YangDerivedInfo>) type).setDataTypeExtendedInfo(yangDerivedInfo);
+
+                    // Add resolution information to the list
+                    YangResolutionInfoImpl resolutionInfo =
+                            new YangResolutionInfoImpl<YangType>(
+                                    type, (YangNode) parentNodeOfLeafList,
+                                    errorLine, errorPosition);
+                    addToResolutionList(resolutionInfo, ctx);
+                }
+                break;
+            case UNION_DATA:
+                YangUnion unionNode = (YangUnion) tmpData;
+                try {
+                    unionNode.addType(type);
+                } catch (DataModelException e) {
+                    ParserException parserException = new ParserException(e.getMessage());
+                    parserException.setLine(ctx.getStart().getLine());
+                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                    throw parserException;
+                }
+
+                /*
+                 * If data type is derived, resolution information to be added
+                 * in resolution list.
+                 */
+                if (yangDataTypes == YangDataTypes.DERIVED) {
+
+                    // Create empty derived info and attach it to type extended info.
+                    YangDerivedInfo<?> yangDerivedInfo = new YangDerivedInfo<>();
+                    ((YangType<YangDerivedInfo>) type).setDataTypeExtendedInfo(yangDerivedInfo);
+
+                    type.setResolvableStatus(UNRESOLVED);
+
+                    // Add resolution information to the list
+                    YangResolutionInfoImpl resolutionInfo =
+                            new YangResolutionInfoImpl<YangType>(
+                                    type, unionNode, errorLine, errorPosition);
+                    addToResolutionList(resolutionInfo, ctx);
+                }
+
+                break;
+            case TYPEDEF_DATA:
+                /* Prepare the base type info and set in derived type */
+                YangTypeDef typeDef = (YangTypeDef) tmpData;
+                typeDef.setDataType(type);
+
+                /*
+                 * If data type is derived, resolution information to be added
+                 * in resolution list.
+                 */
+                if (yangDataTypes == YangDataTypes.DERIVED) {
+                    // Create empty derived info and attach it to type extended info.
+                    YangDerivedInfo<?> yangDerivedInfo = new YangDerivedInfo<>();
+                    ((YangType<YangDerivedInfo>) type).setDataTypeExtendedInfo(yangDerivedInfo);
+
+                    type.setResolvableStatus(UNRESOLVED);
+                    // Add resolution information to the list
+                    YangResolutionInfoImpl resolutionInfo =
+                            new YangResolutionInfoImpl<YangType>(
+                                    type, typeDef, errorLine, errorPosition);
+                    addToResolutionList(resolutionInfo, ctx);
+                }
+                break;
+            //TODO: deviate replacement statement.
+
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                        ctx.string().getText(), EXIT));
+        }
+
+        // Push the type to the stack.
+        listener.getParsedDataStack().push(type);
+    }
+
+    /**
+     * Sets the default require instance value as true when the type is instance identifier.
+     *
+     * @param type type to which the value has to be set
+     */
+    private static void setDefaultRequireInstanceForInstanceIdentifier(YangType<?> type) {
+
+        if (type.getDataType() == YangDataTypes.INSTANCE_IDENTIFIER) {
+            ((YangType<Boolean>) type).setDataTypeExtendedInfo(true);
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (type), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processTypeExit(TreeWalkListener listener,
+                                       GeneratedYangParser.TypeStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_CURRENT_HOLDER, TYPE_DATA, ctx.string().getText(), EXIT);
+
+        Parsable parsableType = listener.getParsedDataStack().pop();
+        if (!(parsableType instanceof YangType)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+    }
+
+    /**
+     * Adds to resolution list.
+     *
+     * @param resolutionInfo resolution information
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangType> resolutionInfo,
+                                            GeneratedYangParser.TypeStatementContext ctx) {
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    TYPE_DATA, ctx.string().getText(), ENTRY, e.getMessage()));
+        }
+    }
+
+    /**
+     * Validates type body statements cardinality.
+     *
+     * @param ctx          context object of the grammar rule
+     * @param yangDataType yang data type
+     */
+    private static void validateTypeSubStatementCardinality(GeneratedYangParser.TypeStatementContext ctx,
+                                                            YangDataTypes yangDataType) {
+        if (ctx.typeBodyStatements() == null || ctx.typeBodyStatements().isEmpty()) {
+            ParserException parserException;
+            switch (yangDataType) {
+                case UNION:
+                    parserException = new ParserException("YANG file error : a type union" +
+                            " must have atleast one type statement.");
+                    break;
+                case ENUMERATION:
+                    parserException = new ParserException("YANG file error : a type enumeration" +
+                            " must have atleast one enum statement.");
+                    break;
+                case BITS:
+                    parserException = new ParserException("YANG file error : a type bits" +
+                            " must have atleast one bit statement.");
+                    break;
+                case DECIMAL64:
+                    parserException = new ParserException("YANG file error : a type decimal64" +
+                            " must have fraction-digits statement.");
+                    break;
+                case LEAFREF:
+                    parserException = new ParserException("YANG file error : a type leafref" +
+                            " must have one path statement.");
+                    break;
+                case IDENTITYREF:
+                    parserException = new ParserException("YANG file error : a type identityref" +
+                            " must have base statement.");
+                    break;
+                default:
+                    return;
+            }
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnionListener.java
new file mode 100644
index 0000000..9653e40
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnionListener.java
@@ -0,0 +1,223 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * type-body-stmts     = numerical-restrictions /
+ *                       decimal64-specification /
+ *                      string-restrictions /
+ *                       enum-specification /
+ *                       leafref-specification /
+ *                       identityref-specification /
+ *                       instance-identifier-specification /
+ *                       bits-specification /
+ *                       union-specification
+ *
+ * union-specification = 1*(type-stmt stmtsep)
+ *
+ * ANTLR grammar rule
+ * typeBodyStatements : numericalRestrictions | stringRestrictions | enumSpecification
+ *                 | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+ *                 | bitsSpecification | unionSpecification;
+ *
+ * unionSpecification : typeStatement+;
+ */
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangType;
+import org.onosproject.yangutils.datamodel.YangTypeDef;
+import org.onosproject.yangutils.datamodel.YangUnion;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.TYPE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangUnionNode;
+
+/**
+ * Represents listener based call back function corresponding to the "union" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class UnionListener {
+
+    /**
+     * Suffix to be used while creating union class.
+     */
+    private static final String UNION_CLASS_SUFFIX = "_union";
+
+    /**
+     * Creates a new union listener.
+     */
+    private UnionListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (union), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processUnionEntry(TreeWalkListener listener,
+                                         GeneratedYangParser.UnionSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, UNION_DATA, "", ENTRY);
+
+        if (listener.getParsedDataStack().peek() instanceof YangType) {
+            YangUnion unionNode = getYangUnionNode(JAVA_GENERATION);
+            Parsable typeData = listener.getParsedDataStack().pop();
+
+            unionNode.setLineNumber(ctx.getStart().getLine());
+            unionNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+            unionNode.setFileName(listener.getFileName());
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, UNION_DATA, "", ENTRY);
+
+            Parsable tmpData = listener.getParsedDataStack().peek();
+
+            switch (tmpData.getYangConstructType()) {
+                case LEAF_DATA:
+                    // Set the name of union same as leaf.
+                    unionNode.setName(((YangLeaf) tmpData).getName() + UNION_CLASS_SUFFIX);
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leaf = listener.getParsedDataStack().pop();
+                    // Add the union node to the parent holder of leaf.
+                    addChildToParentNode(listener, unionNode);
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leaf);
+                    break;
+                case LEAF_LIST_DATA:
+                    // Set the name of union same as leaf list.
+                    unionNode.setName(((YangLeafList) tmpData).getName() + UNION_CLASS_SUFFIX);
+                    // Pop the stack entry to obtain the parent YANG node.
+                    Parsable leafList = listener.getParsedDataStack().pop();
+                    // Add the union node to the parent holder of leaf.
+                    addChildToParentNode(listener, unionNode);
+                    // Push the popped entry back to the stack.
+                    listener.getParsedDataStack().push(leafList);
+                    break;
+                case UNION_DATA:
+                    YangUnion parentUnion = (YangUnion) tmpData;
+                    /*
+                     * In case parent of union is again a union, name of the
+                     * child union is parent union name suffixed with running
+                     * integer number, this is done because under union there
+                     * could be multiple child union types.
+                     */
+                    unionNode.setName(parentUnion.getName() + UNION_CLASS_SUFFIX + parentUnion.getChildUnionNumber());
+                    // Increment the running number.
+                    parentUnion.setChildUnionNumber(parentUnion.getChildUnionNumber() + 1);
+                    // Add union as a child to parent union.
+                    addChildToParentNode(listener, unionNode);
+                    break;
+                case TYPEDEF_DATA:
+                    YangTypeDef typeDef = (YangTypeDef) tmpData;
+                    // Set the name of union same as typedef name.
+                    unionNode.setName(typeDef.getName() + UNION_CLASS_SUFFIX);
+                    // Add union as a child to parent type def.
+                    addChildToParentNode(listener, unionNode);
+                    break;
+                // TODO deviate.
+                default:
+                    throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, TYPE_DATA,
+                            ((YangType<?>) typeData).getDataTypeName(), ENTRY));
+            }
+            listener.getParsedDataStack().push(typeData);
+            listener.getParsedDataStack().push(unionNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, UNION_DATA, "", ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (union), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processUnionExit(TreeWalkListener listener,
+                                        GeneratedYangParser.UnionSpecificationContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, UNION_DATA, "", EXIT);
+
+        Parsable tmpUnionNode = listener.getParsedDataStack().peek();
+        if (tmpUnionNode instanceof YangUnion) {
+            YangUnion unionNode = (YangUnion) tmpUnionNode;
+            listener.getParsedDataStack().pop();
+
+            // Check for stack to be non empty.
+            checkStackIsNotEmpty(listener, MISSING_HOLDER, UNION_DATA, "", EXIT);
+
+            Parsable tmpNode = listener.getParsedDataStack().peek();
+            switch (tmpNode.getYangConstructType()) {
+                case TYPE_DATA: {
+                    YangType<YangUnion> typeNode = (YangType<YangUnion>) tmpNode;
+                    typeNode.setDataTypeExtendedInfo(unionNode);
+                    break;
+                }
+                default:
+                    throw new ParserException(
+                            constructListenerErrorMessage(INVALID_HOLDER, UNION_DATA, "", EXIT));
+            }
+        } else {
+            throw new ParserException(
+                    constructListenerErrorMessage(MISSING_CURRENT_HOLDER, UNION_DATA, "", EXIT));
+        }
+    }
+
+    /**
+     * Adds the union node to the parent holder.
+     *
+     * @param listener listener's object
+     * @param unionNode union node which needs to be added to parent
+     */
+    private static void addChildToParentNode(TreeWalkListener listener, YangUnion unionNode) {
+        if (!(listener.getParsedDataStack().peek() instanceof YangNode)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, UNION_DATA,
+                    "", ENTRY));
+        } else {
+            YangNode curNode = (YangNode) listener.getParsedDataStack().peek();
+            try {
+                curNode.addChild(unionNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        UNION_DATA, "", ENTRY, e.getMessage()));
+            }
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UniqueListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UniqueListener.java
new file mode 100644
index 0000000..59920fe
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UniqueListener.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNIQUE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction
+        .constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * unique-stmt         = unique-keyword sep unique-arg-str stmtend
+ *
+ * ANTLR grammar rule
+ * uniqueStatement: UNIQUE_KEYWORD unique STMTEND;
+ * unique : string;
+ */
+
+/**
+ * Represesnts listener based call back function corresponding to the "unique" rule
+ * defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class UniqueListener {
+
+    /**
+     * Creates a new unique listener.
+     */
+    private UniqueListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (unique), perform validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processUniqueEntry(TreeWalkListener listener,
+                                          GeneratedYangParser.UniqueStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, UNIQUE_DATA, ctx.unique().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        if (listener.getParsedDataStack().peek() instanceof YangList) {
+            YangList yangList = (YangList) tmpData;
+            String tmpUniqueValue = removeQuotesAndHandleConcat(ctx.unique().getText());
+
+            if (tmpUniqueValue.contains(" ")) {
+                String[] uniqueValues = tmpUniqueValue.split(" ");
+                for (String uniqueValue : uniqueValues) {
+                    try {
+                        yangList.addUnique(uniqueValue);
+                    } catch (DataModelException e) {
+                        throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                                UNIQUE_DATA,
+                                ctx.unique().getText(), ENTRY, e.getMessage()));
+                    }
+                }
+            } else {
+                try {
+                    yangList.addUnique(tmpUniqueValue);
+                } catch (DataModelException e) {
+                    throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA, UNIQUE_DATA,
+                            ctx.unique().getText(), ENTRY, e.getMessage()));
+                }
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, UNIQUE_DATA, ctx.unique().getText(),
+                    ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java
new file mode 100644
index 0000000..e7acccf
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UnitsListener.java
@@ -0,0 +1,87 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafList;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.UNITS_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * units-stmt          = units-keyword sep string optsep stmtend
+ *
+ * ANTLR grammar rule
+ * unitsStatement : UNITS_KEYWORD string STMTEND;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "units"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class UnitsListener {
+
+    /**
+     * Creates a new units listener.
+     */
+    private UnitsListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar
+     * rule (units), performs validation and updates the data model
+     * tree.
+     *
+     * @param listener listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processUnitsEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.UnitsStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, UNITS_DATA, ctx.string().getText(), ENTRY);
+
+        Parsable tmpData = listener.getParsedDataStack().peek();
+        switch (tmpData.getYangConstructType()) {
+            case LEAF_DATA:
+                YangLeaf leaf = (YangLeaf) tmpData;
+                leaf.setUnits(ctx.string().getText());
+                break;
+            case LEAF_LIST_DATA:
+                YangLeafList leafList = (YangLeafList) tmpData;
+                leafList.setUnits(ctx.string().getText());
+                break;
+            case TYPEDEF_DATA:
+                // TODO
+                break;
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, UNITS_DATA,
+                                ctx.string().getText(), ENTRY));
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UsesListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UsesListener.java
new file mode 100644
index 0000000..2609d44
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/UsesListener.java
@@ -0,0 +1,228 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangContainer;
+import org.onosproject.yangutils.datamodel.YangGrouping;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.YangUses;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.linker.impl.YangResolutionInfoImpl;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
+import static org.onosproject.yangutils.datamodel.utils.GeneratedLanguage.JAVA_GENERATION;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.DESCRIPTION_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.REFERENCE_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.STATUS_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.USES_DATA;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.WHEN_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerCollisionDetector.detectCollidingChildUtil;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.UNHANDLED_PARSED_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNodeIdentifier;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.validateCardinalityMaxOne;
+import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangUsesNode;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * data-def-stmt       = container-stmt /
+ *                      leaf-stmt /
+ *                      leaf-list-stmt /
+ *                      list-stmt /
+ *                      choice-stmt /
+ *                      anyxml-stmt /
+ *                      uses-stmt
+ *
+ * uses-stmt           = uses-keyword sep identifier-ref-arg-str optsep
+ *                       (";" /
+ *                        "{" stmtsep
+ *                            ;; these stmts can appear in any order
+ *                            [when-stmt stmtsep]
+ *                            *(if-feature-stmt stmtsep)
+ *                            [status-stmt stmtsep]
+ *                            [description-stmt stmtsep]
+ *                            [reference-stmt stmtsep]
+ *                            *(refine-stmt stmtsep)
+ *                            *(uses-augment-stmt stmtsep)
+ *                        "}")
+ *
+ * ANTLR grammar rule
+ * dataDefStatement : containerStatement
+ *                 | leafStatement
+ *                 | leafListStatement
+ *                 | listStatement
+ *                 | choiceStatement
+ *                 | usesStatement;
+ *
+ * usesStatement : USES_KEYWORD string (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement
+ *                 | statusStatement | descriptionStatement | referenceStatement | refineStatement
+ *                 | usesAugmentStatement)* RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "uses"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class UsesListener {
+
+    /**
+     * Creates a new uses listener.
+     */
+    private UsesListener() {
+    }
+
+    /**
+     * It is called when parser enters grammar rule (uses), it perform
+     * validations and updates the data model tree.
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processUsesEntry(TreeWalkListener listener, GeneratedYangParser.UsesStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, USES_DATA, ctx.string().getText(), ENTRY);
+
+        // Validate sub statement cardinality.
+        validateSubStatementsCardinality(ctx);
+
+        // Check for identifier collision
+        int line = ctx.getStart().getLine();
+        int charPositionInLine = ctx.getStart().getCharPositionInLine();
+
+        detectCollidingChildUtil(listener, line, charPositionInLine, ctx.string().getText(), USES_DATA);
+        Parsable curData = listener.getParsedDataStack().peek();
+
+        if (curData instanceof YangModule || curData instanceof YangSubModule
+                || curData instanceof YangContainer || curData instanceof YangList
+                || curData instanceof YangUses || curData instanceof YangAugment
+                || curData instanceof YangCase || curData instanceof YangGrouping
+                || curData instanceof YangInput || curData instanceof YangOutput
+                || curData instanceof YangNotification) {
+
+            YangUses usesNode = getYangUsesNode(JAVA_GENERATION);
+
+            usesNode.setLineNumber(ctx.getStart().getLine());
+            usesNode.setCharPosition(ctx.getStart().getCharPositionInLine());
+            usesNode.setFileName(listener.getFileName());
+            YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(ctx.string().getText(), USES_DATA, ctx);
+            usesNode.setNodeIdentifier(nodeIdentifier);
+            usesNode.setCurrentGroupingDepth(listener.getGroupingDepth());
+            YangNode curNode = (YangNode) curData;
+
+            try {
+                curNode.addChild(usesNode);
+            } catch (DataModelException e) {
+                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                        USES_DATA, ctx.string().getText(), ENTRY, e.getMessage()));
+            }
+            listener.getParsedDataStack().push(usesNode);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    USES_DATA, ctx.string().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * It is called when parser exits from grammar rule (uses), it perform
+     * validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processUsesExit(TreeWalkListener listener,
+                                       GeneratedYangParser.UsesStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, USES_DATA, ctx.string().getText(), EXIT);
+
+        Parsable parsableUses = listener.getParsedDataStack().pop();
+        if (!(parsableUses instanceof YangUses)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, USES_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+        YangUses uses = (YangUses) parsableUses;
+        int errorLine = ctx.getStart().getLine();
+        int errorPosition = ctx.getStart().getCharPositionInLine();
+
+        // Parent YANG node of uses to be added in resolution information.
+        Parsable parentNode = listener.getParsedDataStack().peek();
+
+        // Verify parent node of leaf
+        if (!(parentNode instanceof YangNode)) {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, USES_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+
+        // Add resolution information to the list
+        YangResolutionInfoImpl resolutionInfo = new YangResolutionInfoImpl<YangUses>(uses,
+                (YangNode) parentNode, errorLine,
+                errorPosition);
+        addToResolutionList(resolutionInfo, ctx);
+    }
+
+    // TODO linker to handle collision scenarios like leaf obtained by uses, conflicts with some existing leaf.
+
+    /**
+     * Validates the cardinality of case sub-statements as per grammar.
+     *
+     * @param ctx context object of the grammar rule
+     */
+    private static void validateSubStatementsCardinality(GeneratedYangParser.UsesStatementContext ctx) {
+        validateCardinalityMaxOne(ctx.whenStatement(), WHEN_DATA, USES_DATA, ctx.string().getText());
+        validateCardinalityMaxOne(ctx.statusStatement(), STATUS_DATA, USES_DATA, ctx.string().getText());
+        validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, USES_DATA, ctx.string().getText());
+        validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, USES_DATA, ctx.string().getText());
+    }
+
+    /**
+     * Add to resolution list.
+     *
+     * @param resolutionInfo resolution information.
+     * @param ctx            context object of the grammar rule
+     */
+    private static void addToResolutionList(YangResolutionInfoImpl<YangUses> resolutionInfo,
+                                            GeneratedYangParser.UsesStatementContext ctx) {
+
+        try {
+            addResolutionInfo(resolutionInfo);
+        } catch (DataModelException e) {
+            throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
+                    USES_DATA, ctx.string().getText(), EXIT, e.getMessage()));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ValueListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ValueListener.java
new file mode 100644
index 0000000..39efa6b
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ValueListener.java
@@ -0,0 +1,125 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * value-stmt = value-keyword sep integer-value stmtend
+ *
+ * ANTLR grammar rule
+ * valueStatement : VALUE_KEYWORD ((MINUS INTEGER) | INTEGER) STMTEND;
+ */
+
+import org.onosproject.yangutils.datamodel.YangEnum;
+import org.onosproject.yangutils.datamodel.YangEnumeration;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.VALUE_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidIntegerValue;
+
+/**
+ * Represents listener based call back function corresponding to the "value"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class ValueListener {
+
+    /**
+     * Creates a new value listener.
+     */
+    private ValueListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (value), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processValueEntry(TreeWalkListener listener, GeneratedYangParser.ValueStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, VALUE_DATA, ctx.value().getText(), ENTRY);
+
+        // Validate value
+        int value = getValidIntegerValue(ctx.value().getText(), VALUE_DATA, ctx);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case ENUM_DATA: {
+                YangEnum enumNode = (YangEnum) tmpNode;
+                if (!isEnumValueValid(listener, ctx, value)) {
+                    ParserException parserException = new ParserException("Duplicate Value Entry");
+                    parserException.setLine(ctx.getStart().getLine());
+                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                    throw parserException;
+                }
+                enumNode.setValue(value);
+                break;
+            }
+            default:
+                throw new ParserException(
+                        constructListenerErrorMessage(INVALID_HOLDER, VALUE_DATA, ctx.value().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Validates ENUM value uniqueness.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     * @param value enum value
+     * @return validation result
+     */
+    private static boolean isEnumValueValid(TreeWalkListener listener, GeneratedYangParser.ValueStatementContext ctx,
+            int value) {
+        Parsable enumNode = listener.getParsedDataStack().pop();
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, VALUE_DATA, ctx.value().getText(), ENTRY);
+
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case ENUMERATION_DATA: {
+                YangEnumeration yangEnumeration = (YangEnumeration) tmpNode;
+                for (YangEnum curEnum : yangEnumeration.getEnumSet()) {
+                    if (value == curEnum.getValue()) {
+                        listener.getParsedDataStack().push(enumNode);
+                        return false;
+                    }
+                }
+                listener.getParsedDataStack().push(enumNode);
+                return true;
+            }
+            default:
+                listener.getParsedDataStack().push(enumNode);
+                throw new ParserException(
+                        constructListenerErrorMessage(INVALID_HOLDER, VALUE_DATA, ctx.value().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
new file mode 100644
index 0000000..80caaa2
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
@@ -0,0 +1,112 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidVersion;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.VERSION_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ * module-header-stmts = ;; these stmts can appear in any order
+ *                       [yang-version-stmt stmtsep]
+ *                        namespace-stmt stmtsep
+ *                        prefix-stmt stmtsep
+ *
+ * submodule-header-stmts =
+ *                            ;; these stmts can appear in any order
+ *                            [yang-version-stmt stmtsep]
+ *                             belongs-to-stmt stmtsep
+ *
+ * yang-version-stmt   = yang-version-keyword sep yang-version-arg-str
+ *                       optsep stmtend
+ *
+ *
+ * ANTLR grammar rule
+ * module_header_statement : yang_version_stmt? namespace_stmt prefix_stmt
+ *                         | yang_version_stmt? prefix_stmt namespace_stmt
+ *                         | namespace_stmt yang_version_stmt? prefix_stmt
+ *                         | namespace_stmt prefix_stmt yang_version_stmt?
+ *                         | prefix_stmt namespace_stmt yang_version_stmt?
+ *                         | prefix_stmt yang_version_stmt? namespace_stmt?
+ *                         ;
+ * submodule_header_statement : yang_version_stmt? belongs_to_stmt
+ *                            | belongs_to_stmt yang_version_stmt?
+ *                            ;
+ * yang_version_stmt : YANG_VERSION_KEYWORD version STMTEND;
+ * version           : string;
+ */
+
+/**
+ * Represents listener based call back function corresponding to the "version"
+ * rule defined in ANTLR grammar file for corresponding ABNF rule in RFC 6020.
+ */
+public final class VersionListener {
+
+    /**
+     * Creates a new version listener.
+     */
+    private VersionListener() {
+    }
+
+    /**
+     * It is called when parser receives an input matching the grammar rule
+     * (version), perform validations and update the data model tree.
+     *
+     * @param listener Listener's object
+     * @param ctx context object of the grammar rule
+     */
+    public static void processVersionEntry(TreeWalkListener listener,
+                                           GeneratedYangParser.YangVersionStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, VERSION_DATA, ctx.version().getText(), ENTRY);
+
+        byte version = getValidVersion(ctx);
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        switch (tmpNode.getYangConstructType()) {
+            case MODULE_DATA: {
+                YangModule module = (YangModule) tmpNode;
+                module.setVersion(version);
+                break;
+            }
+            case SUB_MODULE_DATA: {
+                YangSubModule subModule = (YangSubModule) tmpNode;
+                subModule.setVersion(version);
+                break;
+            }
+            default:
+                throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, VERSION_DATA,
+                        ctx.version().getText(), ENTRY));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/WhenListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/WhenListener.java
new file mode 100644
index 0000000..218440f
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/WhenListener.java
@@ -0,0 +1,123 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.listeners;
+
+import org.onosproject.yangutils.datamodel.YangWhen;
+import org.onosproject.yangutils.datamodel.YangWhenHolder;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.WHEN_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_CURRENT_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
+
+/*
+ * Reference: RFC6020 and YANG ANTLR Grammar
+ *
+ * ABNF grammar as per RFC6020
+ *
+ *  when-stmt           = when-keyword sep string optsep
+ *                        (";" /
+ *                         "{" stmtsep
+ *                             ;; these stmts can appear in any order
+ *                             [description-stmt stmtsep]
+ *                             [reference-stmt stmtsep]
+ *                          "}")
+ *
+ * ANTLR grammar rule
+ * whenStatement : WHEN_KEYWORD string (STMTEND | LEFT_CURLY_BRACE ((descriptionStatement? referenceStatement?)
+ *       | (referenceStatement? descriptionStatement?)) RIGHT_CURLY_BRACE);
+ */
+
+/**
+ * Represents listener based call back function corresponding to the
+ * "when" rule defined in ANTLR grammar file for corresponding ABNF rule
+ * in RFC 6020.
+ */
+public final class WhenListener {
+
+    /**
+     * Creates a new when listener.
+     */
+    private WhenListener() {
+    }
+
+    /**
+     * Perform validations and updates the data model tree.It is called when parser
+     * receives an input matching the grammar rule (when).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processWhenEntry(TreeWalkListener listener,
+                                        GeneratedYangParser.WhenStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, WHEN_DATA, ctx.string().getText(), ENTRY);
+        String condition = removeQuotesAndHandleConcat(ctx.string().getText());
+
+        YangWhenHolder whenHolder;
+
+        // Obtain the node of the stack.
+        Parsable tmpNode = listener.getParsedDataStack().peek();
+        if (tmpNode instanceof YangWhenHolder) {
+            whenHolder = (YangWhenHolder) tmpNode;
+
+            YangWhen when = new YangWhen();
+            when.setCondition(condition);
+
+            when.setLineNumber(ctx.getStart().getLine());
+            when.setCharPosition(ctx.getStart().getCharPositionInLine());
+            when.setFileName(listener.getFileName());
+
+            whenHolder.setWhen(when);
+            listener.getParsedDataStack().push(when);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER,
+                    WHEN_DATA, ctx.string().getText(), ENTRY));
+        }
+    }
+
+    /**
+     * Performs validation and updates the data model tree.It is called when parser
+     * exits from grammar rule (when).
+     *
+     * @param listener listener's object
+     * @param ctx      context object of the grammar rule
+     */
+    public static void processWhenExit(TreeWalkListener listener,
+                                       GeneratedYangParser.WhenStatementContext ctx) {
+
+        // Check for stack to be non empty.
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, WHEN_DATA, ctx.string().getText(), EXIT);
+
+        if (listener.getParsedDataStack().peek() instanceof YangWhen) {
+            listener.getParsedDataStack().pop();
+        } else {
+            throw new ParserException(constructListenerErrorMessage(MISSING_CURRENT_HOLDER, WHEN_DATA,
+                    ctx.string().getText(), EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/package-info.java
new file mode 100644
index 0000000..240cd55
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/listeners/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Provide call back functions for listeners based tree walk.
+ */
+package org.onosproject.yangutils.parser.impl.listeners;
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/package-info.java
new file mode 100644
index 0000000..d935f7b
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+/**
+ * Parse the YANG information from ANTLR generated parse tree.
+ */
+package org.onosproject.yangutils.parser.impl;
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerCollisionDetector.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerCollisionDetector.java
new file mode 100644
index 0000000..632f50d
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerCollisionDetector.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+import org.onosproject.yangutils.datamodel.CollisionDetector;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.EXIT;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+
+/**
+ * Represents the detector of YANG construct collision in a YANG file.
+ */
+public final class ListenerCollisionDetector {
+
+    /**
+     * Creates a new listener collision.
+     */
+    private ListenerCollisionDetector() {
+    }
+
+    /**
+     * Detects that the identifiers of all these child nodes must be unique
+     * within all cases in a choice.
+     *
+     * @param listener listener's object
+     * @param line line of identifier in YANG file, required for error
+     *            reporting
+     * @param charPosition character position of identifier in YANG file,
+     *            required for error reporting
+     * @param identifierName name for which uniqueness is to be detected
+     * @param constructType type of YANG construct for which collision check is
+     *            to be performed
+     * @throws ParserException if identifier is not unique
+     */
+    public static void detectCollidingChildUtil(TreeWalkListener listener, int line, int charPosition,
+            String identifierName, YangConstructType constructType)
+            throws ParserException {
+
+        if (listener.getParsedDataStack().peek() instanceof CollisionDetector) {
+            try {
+                ((CollisionDetector) listener.getParsedDataStack().peek()).detectCollidingChild(
+                        identifierName, constructType);
+            } catch (DataModelException e) {
+                ParserException parserException = new ParserException(e.getMessage());
+                parserException.setLine(line);
+                parserException.setCharPosition(charPosition);
+                throw parserException;
+            }
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, constructType, identifierName,
+                    EXIT));
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorLocation.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorLocation.java
new file mode 100644
index 0000000..c1c2888
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorLocation.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+/**
+ * Represents listener error location.
+ */
+public enum ListenerErrorLocation {
+    /**
+     * Represents that the error location is before processing.
+     */
+    ENTRY(),
+
+    /**
+     * Represents that the error location is before processing.
+     */
+    EXIT();
+
+    /**
+     * Returns the message corresponding to listener error location.
+     *
+     * @param errorLocation enum value for type of error
+     * @return message corresponding to listener error location
+     */
+    public static String getErrorLocationMessage(ListenerErrorLocation errorLocation) {
+
+        switch (errorLocation) {
+            case ENTRY:
+                return "before";
+            case EXIT:
+                return "after";
+            default:
+                return "during";
+        }
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorMessageConstruction.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorMessageConstruction.java
new file mode 100644
index 0000000..15b2170
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorMessageConstruction.java
@@ -0,0 +1,92 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.getYangConstructType;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.getErrorLocationMessage;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.getErrorType;
+
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+
+/**
+ * Represents a utility to help construct detailed error message.
+ */
+public final class ListenerErrorMessageConstruction {
+
+    /**
+     * Creates a object of listen error message.
+     */
+    private ListenerErrorMessageConstruction() {
+    }
+
+    /**
+     * Constructs message for error with extended information and returns the
+     * same.
+     *
+     * @param errorType error type needs to be set in error message
+     * @param yangConstructType type of parsable data in which error occurred
+     * @param parsableDataTypeName identifier/string of parsable data type in
+     *            which error occurred
+     * @param errorLocation location where error occurred
+     * @param extendedErrorInformation extended error information
+     * @return constructed error message
+     */
+    public static String constructExtendedListenerErrorMessage(ListenerErrorType errorType,
+                                                               YangConstructType yangConstructType,
+                                                               String parsableDataTypeName,
+                                                               ListenerErrorLocation errorLocation,
+                                                               String extendedErrorInformation) {
+        String newErrorMessage;
+        newErrorMessage = constructListenerErrorMessage(errorType, yangConstructType, parsableDataTypeName,
+                                                        errorLocation)
+                + "\n"
+                + "Error Information: "
+                + extendedErrorInformation;
+        return newErrorMessage;
+    }
+
+    /**
+     * Constructs message for error during listener based tree walk and returns
+     * the same.
+     *
+     * @param errorType error type needs to be set in error message
+     * @param yangConstructType type of parsable data in which error occurred
+     * @param parsableDataTypeName identifier/string of parsable data type in
+     *            which error occurred
+     * @param errorLocation location where error occurred
+     * @return constructed error message
+     */
+    public static String constructListenerErrorMessage(ListenerErrorType errorType,
+                                                       YangConstructType yangConstructType,
+                                                       String parsableDataTypeName,
+                                                       ListenerErrorLocation errorLocation) {
+
+        String errorMessage;
+
+        errorMessage = "Internal parser error detected: " + getErrorType(errorType) + " "
+                + getYangConstructType(yangConstructType);
+
+        if (!parsableDataTypeName.isEmpty()) {
+            errorMessage = errorMessage + " \"" + parsableDataTypeName + "\" ";
+        } else {
+            errorMessage = errorMessage + " ";
+
+        }
+        errorMessage = errorMessage + getErrorLocationMessage(errorLocation) + " processing.";
+        return errorMessage;
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorType.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorType.java
new file mode 100644
index 0000000..f1cb284
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerErrorType.java
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+/**
+ * Represents listener error type.
+ */
+public enum ListenerErrorType {
+    /**
+     * Represents the parent holder in parsable stack for given YANG construct
+     * is invalid.
+     */
+    INVALID_HOLDER(),
+
+    /**
+     * Represents the parent holder in parsable stack for given YANG construct
+     * is missing.
+     */
+    MISSING_HOLDER(),
+
+    /**
+     * Represents the current holder in parsable stack for given YANG construct
+     * is missing.
+     */
+    MISSING_CURRENT_HOLDER(),
+
+    /**
+     * Represents that the child in parsable stack for given YANG construct is
+     * invalid.
+     */
+    INVALID_CHILD(),
+
+    /**
+     * Represents that the cardinality for given YANG construct is invalid.
+     */
+    INVALID_CARDINALITY(),
+
+    /**
+     * Represents that the entry is duplicate.
+     */
+    DUPLICATE_ENTRY(),
+
+    /**
+     * Represents that the content is invalid.
+     */
+    INVALID_CONTENT(),
+
+    /**
+     * Represents that the identifier collision is detected.
+     */
+    IDENTIFIER_COLLISION(),
+
+    /**
+     * Represents that some of earlier parsed data is not handled correctly.
+     */
+    UNHANDLED_PARSED_DATA();
+
+    /**
+     * Returns the message corresponding to listener error type.
+     *
+     * @param errorType enum value for type of error
+     * @return message corresponding to listener error type
+     */
+    public static String getErrorType(ListenerErrorType errorType) {
+
+        switch (errorType) {
+            case INVALID_HOLDER:
+                return "Invalid holder for";
+            case MISSING_HOLDER:
+                return "Missing holder at";
+            case MISSING_CURRENT_HOLDER:
+                return "Missing";
+            case INVALID_CHILD:
+                return "Invalid child in";
+            case INVALID_CARDINALITY:
+                return "Invalid cardinality in";
+            case DUPLICATE_ENTRY:
+                return "Duplicate";
+            case INVALID_CONTENT:
+                return "Invalid content in";
+            case IDENTIFIER_COLLISION:
+                return "Identifier collision detected for";
+            case UNHANDLED_PARSED_DATA:
+                return "Unhandled parsed data at";
+            default:
+                return "Problem in";
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
new file mode 100644
index 0000000..df1dcad
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
@@ -0,0 +1,1058 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.onosproject.yangutils.datamodel.YangAtomicPath;
+import org.onosproject.yangutils.datamodel.YangImport;
+import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangLeafRef;
+import org.onosproject.yangutils.datamodel.YangLeavesHolder;
+import org.onosproject.yangutils.datamodel.YangList;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeIdentifier;
+import org.onosproject.yangutils.datamodel.YangPathPredicate;
+import org.onosproject.yangutils.datamodel.YangReferenceResolver;
+import org.onosproject.yangutils.datamodel.YangRelativePath;
+import org.onosproject.yangutils.datamodel.YangSubModule;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.regex.Pattern;
+
+import static org.onosproject.yangutils.datamodel.YangPathArgType.ABSOLUTE_PATH;
+import static org.onosproject.yangutils.datamodel.YangPathArgType.RELATIVE_PATH;
+import static org.onosproject.yangutils.datamodel.YangPathOperator.EQUALTO;
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.getYangConstructType;
+import static org.onosproject.yangutils.utils.UtilConstants.ADD;
+import static org.onosproject.yangutils.utils.UtilConstants.ANCESTOR_ACCESSOR;
+import static org.onosproject.yangutils.utils.UtilConstants.ANCESTOR_ACCESSOR_IN_PATH;
+import static org.onosproject.yangutils.utils.UtilConstants.CARET;
+import static org.onosproject.yangutils.utils.UtilConstants.CHAR_OF_CLOSE_SQUARE_BRACKET;
+import static org.onosproject.yangutils.utils.UtilConstants.CHAR_OF_OPEN_SQUARE_BRACKET;
+import static org.onosproject.yangutils.utils.UtilConstants.CHAR_OF_SLASH;
+import static org.onosproject.yangutils.utils.UtilConstants.CLOSE_PARENTHESIS;
+import static org.onosproject.yangutils.utils.UtilConstants.COLON;
+import static org.onosproject.yangutils.utils.UtilConstants.CURRENT;
+import static org.onosproject.yangutils.utils.UtilConstants.EMPTY_STRING;
+import static org.onosproject.yangutils.utils.UtilConstants.FALSE;
+import static org.onosproject.yangutils.utils.UtilConstants.OPEN_SQUARE_BRACKET;
+import static org.onosproject.yangutils.utils.UtilConstants.QUOTES;
+import static org.onosproject.yangutils.utils.UtilConstants.SLASH;
+import static org.onosproject.yangutils.utils.UtilConstants.SLASH_FOR_STRING;
+import static org.onosproject.yangutils.utils.UtilConstants.TRUE;
+import static org.onosproject.yangutils.utils.UtilConstants.YANG_FILE_ERROR;
+
+/**
+ * Represents an utility for listener.
+ */
+public final class ListenerUtil {
+
+    private static final Pattern IDENTIFIER_PATTERN = Pattern.compile("[a-zA-Z_][a-zA-Z0-9_.-]*");
+    private static final String DATE_PATTERN = "[0-9]{4}-([0-9]{2}|[0-9])-([0-9]{2}|[0-9])";
+    private static final String NON_NEGATIVE_INTEGER_PATTERN = "[0-9]+";
+    private static final Pattern INTEGER_PATTERN = Pattern.compile("[-][0-9]+|[0-9]+");
+    private static final Pattern PATH_PREDICATE_PATTERN = Pattern.compile("\\[(.*?)\\]");
+    private static final String XML = "xml";
+    private static final String ONE = "1";
+    private static final int IDENTIFIER_LENGTH = 64;
+    private static final String DATE_FORMAT = "yyyy-MM-dd";
+    private static final Log log = LogFactory.getLog(ListenerUtil.class);
+
+    /**
+     * Creates a new listener util.
+     */
+    private ListenerUtil() {
+    }
+
+    /**
+     * Removes doubles quotes and concatenates if string has plus symbol.
+     *
+     * @param yangStringData string from yang file
+     * @return concatenated string after removing double quotes
+     */
+    public static String removeQuotesAndHandleConcat(String yangStringData) {
+
+        yangStringData = yangStringData.replace("\"", EMPTY_STRING);
+        String[] tmpData = yangStringData.split(Pattern.quote(ADD));
+        StringBuilder builder = new StringBuilder();
+        for (String yangString : tmpData) {
+            builder.append(yangString);
+        }
+        return builder.toString();
+    }
+
+    /**
+     * Validates identifier and returns concatenated string if string contains plus symbol.
+     *
+     * @param identifier    string from yang file
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           yang construct's context to get the line number and character position
+     * @return concatenated string after removing double quotes
+     */
+    public static String getValidIdentifier(String identifier, YangConstructType yangConstruct, ParserRuleContext ctx) {
+
+        String identifierString = removeQuotesAndHandleConcat(identifier);
+        ParserException parserException;
+
+        if (identifierString.length() > IDENTIFIER_LENGTH) {
+            parserException = new ParserException("YANG file error : " +
+                                                          getYangConstructType(yangConstruct) + " name " + identifierString + " is " +
+                                                          "greater than 64 characters.");
+        } else if (!IDENTIFIER_PATTERN.matcher(identifierString).matches()) {
+            parserException = new ParserException("YANG file error : " +
+                                                          getYangConstructType(yangConstruct) + " name " + identifierString + " is not " +
+                                                          "valid.");
+        } else if (identifierString.toLowerCase().startsWith(XML)) {
+            parserException = new ParserException("YANG file error : " +
+                                                          getYangConstructType(yangConstruct) + " identifier " + identifierString +
+                                                          " must not start with (('X'|'x') ('M'|'m') ('L'|'l')).");
+        } else {
+            return identifierString;
+        }
+
+        parserException.setLine(ctx.getStart().getLine());
+        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+        throw parserException;
+    }
+
+    /**
+     * Validates identifier and returns concatenated string if string contains plus symbol.
+     *
+     * @param identifier    string from yang file
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           yang construct's context to get the line number and character position
+     * @param yangLeafRef   instance of leafref where the path argument has to be set
+     * @return concatenated string after removing double quotes
+     */
+    public static String getValidIdentifierForLeafref(String identifier, YangConstructType yangConstruct,
+                                                      ParserRuleContext ctx, YangLeafRef yangLeafRef) {
+
+        String identifierString = removeQuotesAndHandleConcat(identifier);
+        ParserException parserException;
+
+        if (identifierString.length() > IDENTIFIER_LENGTH) {
+            parserException = new ParserException("YANG file error : " + " identifier " + identifierString + " in " +
+                                                          getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() + " is " +
+                                                          "greater than 64 characters.");
+        } else if (!IDENTIFIER_PATTERN.matcher(identifierString).matches()) {
+            parserException = new ParserException("YANG file error : " + " identifier " + identifierString + " in " +
+                                                          getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() + " is not " +
+                                                          "valid.");
+        } else if (identifierString.toLowerCase().startsWith(XML)) {
+            parserException = new ParserException("YANG file error : " + " identifier " + identifierString + " in " +
+                                                          getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() +
+                                                          " must not start with (('X'|'x') ('M'|'m') ('L'|'l')).");
+        } else {
+            return identifierString;
+        }
+
+        parserException.setLine(ctx.getStart().getLine());
+        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+        throw parserException;
+    }
+
+    /**
+     * Validates the revision date.
+     *
+     * @param dateToValidate input revision date
+     * @return validation result, true for success, false for failure
+     */
+    public static boolean isDateValid(String dateToValidate) {
+        if (dateToValidate == null || !dateToValidate.matches(DATE_PATTERN)) {
+            return false;
+        }
+
+        SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
+        sdf.setLenient(false);
+
+        try {
+            //if not valid, it will throw ParseException
+            sdf.parse(dateToValidate);
+        } catch (ParseException e) {
+            return false;
+        }
+
+        return true;
+    }
+
+    /**
+     * Validates YANG version.
+     *
+     * @param ctx version context object of the grammar rule
+     * @return valid version
+     */
+    public static byte getValidVersion(GeneratedYangParser.YangVersionStatementContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(ctx.version().getText());
+        if (!value.equals(ONE)) {
+            ParserException parserException = new ParserException("YANG file error: Input version not supported");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        return Byte.valueOf(value);
+    }
+
+    /**
+     * Validates non negative integer value.
+     *
+     * @param integerValue  integer to be validated
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           context object of the grammar rule
+     * @return valid non negative integer value
+     */
+    public static int getValidNonNegativeIntegerValue(String integerValue, YangConstructType yangConstruct,
+                                                      ParserRuleContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(integerValue);
+        if (!value.matches(NON_NEGATIVE_INTEGER_PATTERN)) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        int valueInInteger;
+        try {
+            valueInInteger = Integer.parseInt(value);
+        } catch (NumberFormatException e) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        return valueInInteger;
+    }
+
+    /**
+     * Validates integer value.
+     *
+     * @param integerValue  integer to be validated
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           context object of the grammar rule
+     * @return valid integer value
+     */
+    public static int getValidIntegerValue(String integerValue, YangConstructType yangConstruct,
+                                           ParserRuleContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(integerValue);
+        if (!INTEGER_PATTERN.matcher(value).matches()) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        int valueInInteger;
+        try {
+            valueInInteger = Integer.parseInt(value);
+        } catch (NumberFormatException e) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        return valueInInteger;
+    }
+
+    /**
+     * Validates boolean value.
+     *
+     * @param booleanValue  value to be validated
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           context object of the grammar rule
+     * @return boolean value either true or false
+     */
+    public static boolean getValidBooleanValue(String booleanValue, YangConstructType yangConstruct,
+                                               ParserRuleContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(booleanValue);
+        if (value.equals(TRUE)) {
+            return true;
+        } else if (value.equals(FALSE)) {
+            return false;
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                                                                          "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Returns current date and makes it in usable format for revision.
+     *
+     * @return usable current date format for revision
+     */
+    public static Date getCurrentDateForRevision() {
+
+        SimpleDateFormat dateFormat = new SimpleDateFormat(DATE_FORMAT);
+
+        Date date = new Date();
+        String dateInString = dateFormat.format(date);
+        try {
+            //if not valid, it will throw ParseException
+            Date now = dateFormat.parse(dateInString);
+            return date;
+        } catch (ParseException e) {
+            ParserException parserException = new ParserException("YANG file error: Input date is not correct");
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks and return valid node identifier.
+     *
+     * @param nodeIdentifierString string from yang file
+     * @param yangConstruct        yang construct for creating error message
+     * @param ctx                  yang construct's context to get the line number and character position
+     * @return valid node identifier
+     */
+    public static YangNodeIdentifier getValidNodeIdentifier(String nodeIdentifierString,
+                                                            YangConstructType yangConstruct, ParserRuleContext ctx) {
+        String tmpIdentifierString = removeQuotesAndHandleConcat(nodeIdentifierString);
+        String[] tmpData = tmpIdentifierString.split(Pattern.quote(COLON));
+        if (tmpData.length == 1) {
+            YangNodeIdentifier nodeIdentifier = new YangNodeIdentifier();
+            nodeIdentifier.setName(getValidIdentifier(tmpData[0], yangConstruct, ctx));
+            return nodeIdentifier;
+        } else if (tmpData.length == 2) {
+            YangNodeIdentifier nodeIdentifier = new YangNodeIdentifier();
+            nodeIdentifier.setPrefix(getValidIdentifier(tmpData[0], yangConstruct, ctx));
+            nodeIdentifier.setName(getValidIdentifier(tmpData[1], yangConstruct, ctx));
+            return nodeIdentifier;
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " name " + nodeIdentifierString +
+                                                                          " is not valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks and return valid node identifier specific to nodes in leafref path.
+     *
+     * @param nodeIdentifierString string from yang file
+     * @param yangConstruct        yang construct for creating error message
+     * @param ctx                  yang construct's context to get the line number and character position
+     * @param yangLeafRef          instance of leafref where the path argument has to be set
+     * @return valid node identifier
+     */
+    public static YangNodeIdentifier getValidNodeIdentifierForLeafref(String nodeIdentifierString,
+                                                                      YangConstructType yangConstruct,
+                                                                      ParserRuleContext ctx, YangLeafRef yangLeafRef) {
+
+        String tmpIdentifierString = removeQuotesAndHandleConcat(nodeIdentifierString);
+        String[] tmpData = tmpIdentifierString.split(Pattern.quote(COLON));
+        if (tmpData.length == 1) {
+            YangNodeIdentifier nodeIdentifier = new YangNodeIdentifier();
+            nodeIdentifier.setName(getValidIdentifierForLeafref(tmpData[0], yangConstruct, ctx, yangLeafRef));
+            return nodeIdentifier;
+        } else if (tmpData.length == 2) {
+            YangNodeIdentifier nodeIdentifier = new YangNodeIdentifier();
+            nodeIdentifier.setPrefix(getValidIdentifierForLeafref(tmpData[0], yangConstruct, ctx, yangLeafRef));
+            nodeIdentifier.setName(getValidIdentifierForLeafref(tmpData[1], yangConstruct, ctx, yangLeafRef));
+            return nodeIdentifier;
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + yangLeafRef.getPath() +
+                                                                          " is not valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Validates the path argument. It can be either absolute or relative path.
+     *
+     * @param pathString    the path string from the path type
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           yang construct's context to get the line number and character position
+     * @param yangLeafRef   instance of leafref where the path argument has to be set
+     */
+    public static void validatePathArgument(String pathString, YangConstructType yangConstruct,
+                                            ParserRuleContext ctx, YangLeafRef yangLeafRef) {
+
+        String completePathString = removeQuotesAndHandleConcat(pathString);
+        yangLeafRef.setPath(completePathString);
+        if (completePathString.startsWith(SLASH)) {
+            yangLeafRef.setPathType(ABSOLUTE_PATH);
+            List<YangAtomicPath> yangAtomicPathListList = validateAbsolutePath(completePathString, yangConstruct, ctx,
+                                                                               yangLeafRef);
+            validatePrefixAndYangNode(yangAtomicPathListList, yangLeafRef);
+            yangLeafRef.setAtomicPath(yangAtomicPathListList);
+        } else if (completePathString.startsWith(ANCESTOR_ACCESSOR)) {
+            yangLeafRef.setPathType(RELATIVE_PATH);
+            validateRelativePath(completePathString, yangConstruct, ctx, yangLeafRef);
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + yangLeafRef.getPath() +
+                                                                          " does not follow valid path syntax");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Validates the prefixes in the leafref and assigns them to the respective imported name in map.
+     *
+     * @param yangAtomicPathList list of atomic poth
+     * @param yangLeafRef        instance YANG leafref
+     */
+    private static void validatePrefixAndYangNode(List<YangAtomicPath> yangAtomicPathList, YangLeafRef yangLeafRef) {
+        Iterator<YangAtomicPath> yangAtomicPathIterator = yangAtomicPathList.listIterator();
+        while (yangAtomicPathIterator.hasNext()) {
+            YangAtomicPath atomicPath = yangAtomicPathIterator.next();
+            String prefix = atomicPath.getNodeIdentifier().getPrefix();
+            YangNode parentNodeOfLeafref = yangLeafRef.getParentNodeOfLeafref();
+            YangNode moduleOrSubModule = getModuleOrSubmoduleInFileOfTheCurrentNode(parentNodeOfLeafref);
+            YangModule moduleNode = null;
+            if (moduleOrSubModule instanceof YangModule) {
+                moduleNode = (YangModule) moduleOrSubModule;
+            }
+            if (moduleNode != null) {
+                updatePrefixWithTheImportedList(moduleNode, prefix, yangLeafRef);
+            }
+        }
+    }
+
+    /**
+     * Updates the prefix with the imported list in the module.
+     *
+     * @param moduleNode   root node of the leafref
+     * @param prefixInPath prefix in the path
+     * @param yangLeafRef  instance YANG leafref
+     */
+    private static void updatePrefixWithTheImportedList(YangModule moduleNode, String prefixInPath, YangLeafRef
+            yangLeafRef) {
+        if (prefixInPath != null && prefixInPath != EMPTY_STRING && !prefixInPath.equals(moduleNode.getPrefix())) {
+            List<YangImport> moduleImportList = moduleNode.getImportList();
+            if (moduleImportList != null && !moduleImportList.isEmpty()) {
+                Iterator<YangImport> yangImportIterator = moduleImportList.listIterator();
+                while (yangImportIterator.hasNext()) {
+                    YangImport yangImport = yangImportIterator.next();
+                    if (yangImport.getPrefixId().equals(prefixInPath)) {
+                        HashMap prefixMap = new HashMap();
+                        prefixMap.put(prefixInPath, yangImport.getModuleName());
+                        yangLeafRef.setPrefixAndItsImportedModule(prefixMap);
+                    }
+                }
+            }
+        } else {
+            HashMap prefixMap = new HashMap();
+            prefixMap.put(prefixInPath, moduleNode.getName());
+            yangLeafRef.setPrefixAndItsImportedModule(prefixMap);
+        }
+    }
+
+    /**
+     * Returns module or submodule node from the current node.
+     *
+     * @param node current node
+     * @return root node
+     */
+    private static YangNode getModuleOrSubmoduleInFileOfTheCurrentNode(YangNode node) {
+        while (!(node instanceof YangModule) && !(node instanceof YangSubModule)) {
+            if (node == null) {
+                throw new ParserException("Internal datamodel error: Datamodel tree is not correct");
+            }
+            node = node.getParent();
+        }
+        return node;
+    }
+
+    /**
+     * Validates the unique syntax from the reference path.
+     *
+     * @param uniquePath   path of unique
+     * @param prefixOfFile current file's prefix
+     * @param ctx          yang construct's context to get the line number and character position
+     * @return list of absolute path
+     */
+    private static List<YangAtomicPath> validateUniqueValues(String uniquePath, String prefixOfFile,
+                                                             ParserRuleContext ctx) {
+        List<YangAtomicPath> atomicPath = new LinkedList<>();
+        String[] pathInUnique = uniquePath.split(SLASH_FOR_STRING);
+        for (String uniqueValue : pathInUnique) {
+            YangAtomicPath yangAtomicPathPath = new YangAtomicPath();
+            YangNodeIdentifier nodeIdentifier = getValidNodeIdentifier(uniqueValue, YangConstructType.UNIQUE_DATA, ctx);
+            yangAtomicPathPath.setNodeIdentifier(nodeIdentifier);
+            atomicPath.add(yangAtomicPathPath);
+            if (nodeIdentifier.getPrefix() != null && nodeIdentifier.getPrefix() != prefixOfFile) {
+                ParserException parserException = new ParserException("YANG file error : A leaf reference, in unique," +
+                                                                              " must refer to a leaf in the list");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+        }
+        return atomicPath;
+    }
+
+    /**
+     * Validates unique field from the list.
+     *
+     * @param yangList instance of YANG list
+     * @param ctx      yang construct's context to get the line number and character position
+     */
+    public static void validateUniqueInList(YangList yangList, ParserRuleContext ctx) {
+        YangLeaf leaf;
+        // Returns the prefix for the file where unique is present.
+        String prefixOfTheFile = getPrefixInFileOfTheCurrentNode(yangList);
+        List<String> uniques = yangList.getUniqueList();
+        if (uniques != null && !uniques.isEmpty()) {
+            Iterator<String> uniqueList = uniques.listIterator();
+            while (uniqueList.hasNext()) {
+                String pathInUnique = uniqueList.next();
+                List<YangAtomicPath> atomicPathInUnique = validateUniqueValues(pathInUnique, prefixOfTheFile, ctx);
+                YangAtomicPath leafInPath = atomicPathInUnique.get(atomicPathInUnique.size() - 1);
+                if (atomicPathInUnique.size() == 1) {
+                    leaf = getReferenceLeafFromUnique(yangList, leafInPath);
+                } else {
+                    atomicPathInUnique.remove(atomicPathInUnique.size() - 1);
+                    YangNode holderOfLeaf = getNodeUnderListFromPath(atomicPathInUnique, yangList, ctx);
+                    leaf = getReferenceLeafFromUnique(holderOfLeaf, leafInPath);
+                }
+                if (leaf == null) {
+                    ParserException parserException = new ParserException("YANG file error : A leaf reference, in " +
+                                                                                  "unique," +
+                                                                                  " must refer to a leaf under the list");
+                    parserException.setLine(ctx.getStart().getLine());
+                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                    throw parserException;
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns the last node under the unique path.
+     *
+     * @param uniquePath atomic path list
+     * @param node       root node from where it starts searching
+     * @param ctx        yang construct's context to get the line number and character position
+     * @return last node in the list
+     */
+    private static YangNode getNodeUnderListFromPath(List<YangAtomicPath> uniquePath, YangNode node,
+                                                     ParserRuleContext ctx) {
+        Iterator<YangAtomicPath> nodesInReference = uniquePath.listIterator();
+        YangNode potentialReferredNode = node.getChild();
+        while (nodesInReference.hasNext()) {
+            YangAtomicPath nodeInUnique = nodesInReference.next();
+            YangNode referredNode = getReferredNodeFromTheUniqueNodes(nodeInUnique.getNodeIdentifier(),
+                                                                      potentialReferredNode);
+            if (referredNode == null) {
+                ParserException parserException = new ParserException("YANG file error : The target node in unique " +
+                                                                              "reference path is invalid");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            } else {
+                potentialReferredNode = referredNode.getChild();
+            }
+        }
+        return potentialReferredNode;
+    }
+
+    /**
+     * Returns the node that matches with the name of the node in path.
+     *
+     * @param nodeInUnique          node name in path
+     * @param potentialReferredNode node under which it has to match
+     * @return referred node
+     */
+    private static YangNode getReferredNodeFromTheUniqueNodes(YangNodeIdentifier nodeInUnique, YangNode
+            potentialReferredNode) {
+        while (potentialReferredNode != null) {
+            // Check if the potential referred node is the actual referred node
+            if (potentialReferredNode.getName().equals(nodeInUnique.getName())) {
+                return potentialReferredNode;
+            }
+            potentialReferredNode = potentialReferredNode.getNextSibling();
+        }
+        return null;
+    }
+
+    /**
+     * Returns the leaf which unique refers.
+     *
+     * @param nodeForLeaf  last node where leaf is referred
+     * @param leafInUnique leaf in unique path
+     * @return YANG leaf
+     */
+    private static YangLeaf getReferenceLeafFromUnique(YangNode nodeForLeaf, YangAtomicPath leafInUnique) {
+        YangLeavesHolder leavesHolder = (YangLeavesHolder) nodeForLeaf;
+        List<YangLeaf> leaves = leavesHolder.getListOfLeaf();
+        if (leaves != null && !leaves.isEmpty()) {
+            for (YangLeaf leaf : leaves) {
+                if (leafInUnique.getNodeIdentifier().getName().equals(leaf.getName())) {
+                    return leaf;
+                }
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Returns the prefix of the current file.
+     *
+     * @param node node where it needs to find the root node
+     * @return prefix of root node
+     */
+    public static String getPrefixInFileOfTheCurrentNode(YangNode node) {
+        String prefixInFile;
+        while (!(node instanceof YangReferenceResolver)) {
+            node = node.getParent();
+            if (node == null) {
+                throw new ParserException("Internal datamodel error: Datamodel tree is not correct");
+            }
+        }
+        if (node instanceof YangModule) {
+            YangModule yangModule = (YangModule) node;
+            prefixInFile = yangModule.getPrefix();
+        } else {
+            YangSubModule yangSubModule = (YangSubModule) node;
+            prefixInFile = yangSubModule.getPrefix();
+        }
+        return prefixInFile;
+    }
+
+    /**
+     * Validates the relative path.
+     *
+     * @param completePathString the path string of relative path
+     * @param yangConstruct      yang construct for creating error message
+     * @param ctx                yang construct's context to get the line number and character position
+     * @param yangLeafRef        instance of leafref where the path argument has to be set
+     */
+    private static void validateRelativePath(String completePathString, YangConstructType yangConstruct,
+                                             ParserRuleContext ctx, YangLeafRef yangLeafRef) {
+
+        YangRelativePath relativePath = new YangRelativePath();
+        int numberOfAncestors = 0;
+        while (completePathString.startsWith(ANCESTOR_ACCESSOR_IN_PATH)) {
+            completePathString = completePathString.replaceFirst(ANCESTOR_ACCESSOR_IN_PATH, EMPTY_STRING);
+            numberOfAncestors = numberOfAncestors + 1;
+        }
+        if (completePathString == null || completePathString.length() == 0) {
+            ParserException parserException = new ParserException("YANG file error : "
+                                                                          + getYangConstructType(yangConstruct) + yangLeafRef.getPath() +
+                                                                          " does not follow valid path syntax");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        relativePath.setAncestorNodeCount(numberOfAncestors);
+        List<YangAtomicPath> atomicPath = validateAbsolutePath(SLASH_FOR_STRING + completePathString,
+                                                               yangConstruct,
+                                                               ctx, yangLeafRef);
+        validatePrefixAndYangNode(atomicPath, yangLeafRef);
+        relativePath.setAtomicPathList(atomicPath);
+        yangLeafRef.setRelativePath(relativePath);
+    }
+
+    /**
+     * Validates the absolute path.
+     *
+     * @param completePathString the path string of absolute path
+     * @param yangConstruct      yang construct for creating error message
+     * @param ctx                yang construct's context to get the line number and character position
+     * @param yangLeafRef        instance of leafref where the path argument has to be set
+     * @return list of object of node in absolute path
+     */
+    private static List<YangAtomicPath> validateAbsolutePath(String completePathString,
+                                                             YangConstructType yangConstruct, ParserRuleContext
+                                                                     ctx, YangLeafRef yangLeafRef) {
+
+        List<YangAtomicPath> absolutePathList = new LinkedList<>();
+        YangPathPredicate yangPathPredicate = new YangPathPredicate();
+        YangNodeIdentifier yangNodeIdentifier;
+
+        while (completePathString != null) {
+            String path = completePathString.replaceFirst(SLASH_FOR_STRING, EMPTY_STRING);
+            if (path == null || path.length() == 0) {
+                ParserException parserException = new ParserException("YANG file error : "
+                                                                              + getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() +
+                                                                              " does not follow valid path syntax");
+                parserException.setLine(ctx.getStart().getLine());
+                parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                throw parserException;
+            }
+            String matchedPathPredicate;
+            String nodeIdentifier;
+            String[] differentiate = new String[2];
+            int forNodeIdentifier = path.indexOf(CHAR_OF_SLASH);
+            int forPathPredicate = path.indexOf(CHAR_OF_OPEN_SQUARE_BRACKET);
+
+            // Checks if path predicate is present for the node.
+            if ((forPathPredicate < forNodeIdentifier) && (forPathPredicate != -1)) {
+                List<String> pathPredicate = new ArrayList<>();
+                matchedPathPredicate = matchForPathPredicate(path);
+
+                if (matchedPathPredicate == null || matchedPathPredicate.length() == 0) {
+                    ParserException parserException = new ParserException("YANG file error : "
+                                                                                  + getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() +
+                                                                                  " does not follow valid path syntax");
+                    parserException.setLine(ctx.getStart().getLine());
+                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                    throw parserException;
+                }
+                int indexOfMatchedFirstOpenBrace = path.indexOf(CHAR_OF_OPEN_SQUARE_BRACKET);
+                differentiate[0] = path.substring(0, indexOfMatchedFirstOpenBrace);
+                differentiate[1] = path.substring(indexOfMatchedFirstOpenBrace);
+                pathPredicate.add(matchedPathPredicate);
+                nodeIdentifier = differentiate[0];
+                // Starts adding all path predicates of a node into the list.
+                if (!differentiate[1].isEmpty()) {
+                    while (differentiate[1].startsWith(OPEN_SQUARE_BRACKET)) {
+                        matchedPathPredicate = matchForPathPredicate(differentiate[1]);
+                        if (matchedPathPredicate == null || matchedPathPredicate.length() == 0) {
+                            ParserException parserException = new ParserException(
+                                    "YANG file error : " + getYangConstructType(yangConstruct) + " "
+                                            + yangLeafRef.getPath() +
+                                            " does not follow valid path syntax");
+                            parserException.setLine(ctx.getStart().getLine());
+                            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                            throw parserException;
+                        }
+                        pathPredicate.add(matchedPathPredicate);
+                        differentiate[1] = differentiate[1].substring(matchedPathPredicate.length());
+                    }
+                }
+
+                List<YangPathPredicate> pathPredicateList = validatePathPredicate(pathPredicate, yangConstruct, ctx,
+                                                                                  yangPathPredicate, yangLeafRef);
+                YangAtomicPath atomicPath = new YangAtomicPath();
+                yangNodeIdentifier = getValidNodeIdentifierForLeafref(nodeIdentifier, yangConstruct, ctx, yangLeafRef);
+                atomicPath.setNodeIdentifier(yangNodeIdentifier);
+                atomicPath.setPathPredicatesList(pathPredicateList);
+                absolutePathList.add(atomicPath);
+            } else {
+                if (path.contains(SLASH_FOR_STRING)) {
+                    nodeIdentifier = path.substring(0, path.indexOf(CHAR_OF_SLASH));
+                    differentiate[1] = path.substring(path.indexOf(CHAR_OF_SLASH));
+                } else {
+                    nodeIdentifier = path;
+                    differentiate[1] = null;
+                }
+                yangNodeIdentifier = getValidNodeIdentifierForLeafref(nodeIdentifier, yangConstruct, ctx, yangLeafRef);
+
+                YangAtomicPath atomicPath = new YangAtomicPath();
+                atomicPath.setNodeIdentifier(yangNodeIdentifier);
+                atomicPath.setPathPredicatesList(null);
+                absolutePathList.add(atomicPath);
+            }
+            if (differentiate[1] == null || differentiate[1].length() == 0) {
+                completePathString = null;
+            } else {
+                completePathString = differentiate[1];
+            }
+        }
+        return absolutePathList;
+    }
+
+    /**
+     * Validates path predicate in the absolute path's node.
+     *
+     * @param pathPredicate     list of path predicates in the node of absolute path
+     * @param yangConstruct     yang construct for creating error message
+     * @param ctx               yang construct's context to get the line number and character position
+     * @param yangPathPredicate instance of path predicate where it has to be set
+     * @param yangLeafRef       instance of leafref where the path argument has to be set
+     * @return list of object of path predicates in absolute path's node
+     */
+    private static List<YangPathPredicate> validatePathPredicate(List<String> pathPredicate,
+                                                                 YangConstructType yangConstruct, ParserRuleContext
+                                                                         ctx, YangPathPredicate yangPathPredicate,
+                                                                 YangLeafRef yangLeafRef) {
+
+        Iterator<String> pathPredicateString = pathPredicate.iterator();
+        List<String> pathEqualityExpression = new ArrayList<>();
+
+        while (pathPredicateString.hasNext()) {
+            String pathPredicateForNode = pathPredicateString.next();
+            pathPredicateForNode = (pathPredicateForNode.substring(1)).trim();
+            pathPredicateForNode = pathPredicateForNode.substring(0,
+                                                                  pathPredicateForNode.indexOf(CHAR_OF_CLOSE_SQUARE_BRACKET));
+            pathEqualityExpression.add(pathPredicateForNode);
+        }
+        List<YangPathPredicate> validatedPathPredicateList = validatePathEqualityExpression(pathEqualityExpression,
+                                                                                            yangConstruct, ctx, yangPathPredicate, yangLeafRef);
+        return validatedPathPredicateList;
+    }
+
+    /**
+     * Validates the path equality expression.
+     *
+     * @param pathEqualityExpression list of path equality expression in the path predicates of the node
+     * @param yangConstruct          yang construct for creating error message
+     * @param ctx                    yang construct's context to get the line number and character position
+     * @param yangPathPredicate      instance of path predicate where it has to be set
+     * @param yangLeafRef            instance of leafref where the path argument has to be set
+     * @return list of object of path predicates in absolute path's node
+     */
+    private static List<YangPathPredicate> validatePathEqualityExpression(List<String> pathEqualityExpression,
+                                                                          YangConstructType yangConstruct,
+                                                                          ParserRuleContext ctx, YangPathPredicate
+                                                                                  yangPathPredicate,
+                                                                          YangLeafRef yangLeafRef) {
+
+        Iterator<String> pathEqualityExpressionString = pathEqualityExpression.iterator();
+        List<YangPathPredicate> yangPathPredicateList = new ArrayList<>();
+
+        while (pathEqualityExpressionString.hasNext()) {
+            String pathEqualityExpressionForNode = pathEqualityExpressionString.next();
+            String[] pathEqualityExpressionArray = pathEqualityExpressionForNode.split("[=]");
+
+            YangNodeIdentifier yangNodeIdentifierForPredicate;
+            YangRelativePath yangRelativePath;
+            yangNodeIdentifierForPredicate = getValidNodeIdentifierForLeafref(pathEqualityExpressionArray[0].trim(),
+                                                                              yangConstruct, ctx, yangLeafRef);
+            yangRelativePath = validatePathKeyExpression(pathEqualityExpressionArray[1].trim(), yangConstruct, ctx,
+                                                         yangLeafRef);
+            yangPathPredicate.setNodeIdentifier(yangNodeIdentifierForPredicate);
+            yangPathPredicate.setPathOperator(EQUALTO);
+            yangPathPredicate.setRightRelativePath(yangRelativePath);
+            yangPathPredicateList.add(yangPathPredicate);
+        }
+        return yangPathPredicateList;
+    }
+
+    /**
+     * Validate the path key expression.
+     *
+     * @param rightRelativePath relative path in the path predicate
+     * @param yangConstruct     yang construct for creating error message
+     * @param ctx               yang construct's context to get the line number and character position
+     * @param yangLeafRef       instance of leafref where the path argument has to be set
+     * @return object of right relative path in path predicate
+     */
+    private static YangRelativePath validatePathKeyExpression(String rightRelativePath,
+                                                              YangConstructType yangConstruct, ParserRuleContext ctx,
+                                                              YangLeafRef yangLeafRef) {
+
+        YangRelativePath yangRelativePath = new YangRelativePath();
+        String[] relativePath = rightRelativePath.split(SLASH_FOR_STRING);
+        List<String> rightAbsolutePath = new ArrayList<>();
+        int accessAncestor = 0;
+        for (String path : relativePath) {
+            if (path.trim().equals(ANCESTOR_ACCESSOR)) {
+                accessAncestor = accessAncestor + 1;
+            } else {
+                rightAbsolutePath.add(path);
+            }
+        }
+        List<YangAtomicPath> atomicPathInRelativePath = validateRelativePathKeyExpression(rightAbsolutePath,
+                                                                                          yangConstruct, ctx, yangLeafRef);
+        yangRelativePath.setAtomicPathList(atomicPathInRelativePath);
+        yangRelativePath.setAncestorNodeCount(accessAncestor);
+        return yangRelativePath;
+    }
+
+    /**
+     * Validates the relative path key expression.
+     *
+     * @param rightAbsolutePath absolute path nodes present in the relative path
+     * @param yangConstruct     yang construct for creating error message
+     * @param ctx               yang construct's context to get the line number and character position
+     * @param yangLeafRef       instance of leafref where the path argument has to be set
+     * @return list of object of absolute path nodes present in the relative path
+     */
+    private static List<YangAtomicPath> validateRelativePathKeyExpression(List<String> rightAbsolutePath,
+                                                                          YangConstructType yangConstruct,
+                                                                          ParserRuleContext ctx, YangLeafRef
+                                                                                  yangLeafRef) {
+
+        List<YangAtomicPath> atomicPathList = new ArrayList<>();
+        YangNodeIdentifier yangNodeIdentifier;
+
+        Iterator<String> nodes = rightAbsolutePath.iterator();
+        String currentInvocationFunction = nodes.next();
+        currentInvocationFunction = currentInvocationFunction.trim();
+        String[] currentFunction = currentInvocationFunction.split("[(]");
+
+        if (!(currentFunction[0].trim().equals(CURRENT)) || !(currentFunction[1].trim().equals(CLOSE_PARENTHESIS))) {
+            ParserException parserException = new ParserException("YANG file error : "
+                                                                          + getYangConstructType(yangConstruct) + " " + yangLeafRef.getPath() +
+                                                                          " does not follow valid path syntax");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        while (nodes.hasNext()) {
+            YangAtomicPath atomicPath = new YangAtomicPath();
+            String node = nodes.next();
+            yangNodeIdentifier = getValidNodeIdentifierForLeafref(node.trim(), yangConstruct, ctx, yangLeafRef);
+            atomicPath.setNodeIdentifier(yangNodeIdentifier);
+            atomicPathList.add(atomicPath);
+        }
+        return atomicPathList;
+    }
+
+    /**
+     * Validates the match for first path predicate in a given string.
+     *
+     * @param matchRequiredString string for which match has to be done
+     * @return the matched string
+     */
+    private static String matchForPathPredicate(String matchRequiredString) {
+
+        String matchedString = null;
+        java.util.regex.Matcher matcher = PATH_PREDICATE_PATTERN.matcher(matchRequiredString);
+        if (matcher.find()) {
+            matchedString = matcher.group(0);
+        }
+        return matchedString;
+    }
+
+    /**
+     * Checks and return valid absolute schema node id.
+     *
+     * @param argumentString    string from yang file
+     * @param yangConstructType yang construct for creating error message
+     * @param ctx               yang construct's context to get the line number and character position
+     * @return target nodes list of absolute schema node id
+     */
+    public static List<YangAtomicPath> getValidAbsoluteSchemaNodeId(String argumentString,
+                                                                    YangConstructType yangConstructType,
+                                                                    ParserRuleContext ctx) {
+
+        List<YangAtomicPath> targetNodes = new ArrayList<>();
+        YangNodeIdentifier yangNodeIdentifier;
+        String tmpSchemaNodeId = removeQuotesAndHandleConcat(argumentString);
+
+        // absolute-schema-nodeid = 1*("/" node-identifier)
+        if (!tmpSchemaNodeId.startsWith(SLASH)) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstructType) + " name " + argumentString +
+                                                                          "is not valid");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+        String[] tmpData = tmpSchemaNodeId.replaceFirst(CARET + SLASH, EMPTY_STRING).split(SLASH);
+        for (String nodeIdentifiers : tmpData) {
+            yangNodeIdentifier = getValidNodeIdentifier(nodeIdentifiers, yangConstructType, ctx);
+            YangAtomicPath yangAbsPath = new YangAtomicPath();
+            yangAbsPath.setNodeIdentifier(yangNodeIdentifier);
+            targetNodes.add(yangAbsPath);
+        }
+        return targetNodes;
+    }
+
+    /**
+     * Throws parser exception for unsupported YANG constructs.
+     *
+     * @param yangConstructType yang construct for creating error message
+     * @param ctx               yang construct's context to get the line number and character position
+     * @param errorInfo         error information
+     * @param fileName          YANG file name
+     */
+    public static void handleUnsupportedYangConstruct(YangConstructType yangConstructType,
+                                                      ParserRuleContext ctx, String errorInfo, String fileName) {
+        ParserException parserException = new ParserException(YANG_FILE_ERROR
+                + QUOTES + getYangConstructType(yangConstructType) + QUOTES
+                + errorInfo);
+        parserException.setLine(ctx.getStart().getLine());
+        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+        log.info(parserException.getMessage() + " at position " + parserException.getCharPositionInLine() +
+                         " in line " + parserException.getLineNumber() + " of yang file " + fileName);
+    }
+
+    /**
+     * Returns date and makes it in usable format for revision.
+     *
+     * @param dateInString date argument string from yang file
+     * @param ctx          yang construct's context to get the line number and character position
+     * @return date format for revision
+     */
+    public static Date getValidDateFromString(String dateInString, ParserRuleContext ctx) {
+        String dateArgument = removeQuotesAndHandleConcat(dateInString);
+        if (!dateArgument.matches(DATE_PATTERN)) {
+            ParserException parserException = new ParserException("YANG file error: Input date is not correct");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        SimpleDateFormat sdf = new SimpleDateFormat(DATE_FORMAT);
+        sdf.setLenient(false);
+
+        try {
+            //if not valid, it will throw ParseException
+            return sdf.parse(dateArgument);
+        } catch (ParseException e) {
+            ParserException parserException = new ParserException("YANG file error: Input date is not correct");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks and return valid prefix.
+     *
+     * @param inputString   string from yang file
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx           yang construct's context to get the line number and character position
+     * @return valid prefix
+     */
+    public static String getValidPrefix(String inputString,
+                                        YangConstructType yangConstruct, ParserRuleContext ctx) {
+        String tmpPrefixString = removeQuotesAndHandleConcat(inputString);
+        String[] tmpData = tmpPrefixString.split(Pattern.quote(COLON));
+        if (tmpData.length == 2) {
+            return tmpData[0];
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                                                                          getYangConstructType(yangConstruct) + " name " + inputString +
+                                                                          " is not valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java
new file mode 100644
index 0000000..fa3b200
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java
@@ -0,0 +1,243 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+import java.util.Iterator;
+import java.util.List;
+
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.onosproject.yangutils.datamodel.YangCase;
+import org.onosproject.yangutils.datamodel.YangChoice;
+import org.onosproject.yangutils.datamodel.YangConfig;
+import org.onosproject.yangutils.datamodel.YangInput;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNotification;
+import org.onosproject.yangutils.datamodel.YangOutput;
+import org.onosproject.yangutils.datamodel.YangRpc;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+
+import static org.onosproject.yangutils.datamodel.utils.YangConstructType.getYangConstructType;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
+
+/**
+ * Represents a utility to carry out listener validation.
+ */
+public final class ListenerValidation {
+
+    /**
+     * Creates a new listener validation.
+     */
+    private ListenerValidation() {
+    }
+
+    /**
+     * Checks parsed data stack is not empty.
+     *
+     * @param listener Listener's object
+     * @param errorType error type needs to be set in error message
+     * @param yangConstructType type of parsable data in which error occurred
+     * @param parsableDataTypeName name of parsable data type in which error
+     *            occurred
+     * @param errorLocation location where error occurred
+     */
+    public static void checkStackIsNotEmpty(TreeWalkListener listener, ListenerErrorType errorType,
+            YangConstructType yangConstructType, String parsableDataTypeName,
+            ListenerErrorLocation errorLocation) {
+
+        if (listener.getParsedDataStack().empty()) {
+            /*
+             * If stack is empty it indicates error condition, value of
+             * parsableDataTypeName will be null in case there is no name
+             * attached to parsable data type.
+             */
+            String message = constructListenerErrorMessage(errorType, yangConstructType, parsableDataTypeName,
+                    errorLocation);
+            throw new ParserException(message);
+        }
+    }
+
+    /**
+     * Checks parsed data stack is empty.
+     *
+     * @param listener Listener's object
+     * @param errorType error type needs to be set in error message
+     * @param yangConstructType type of parsable data in which error occurred
+     * @param parsableDataTypeName name of parsable data type in which error
+     *            occurred
+     * @param errorLocation location where error occurred
+     */
+    public static void checkStackIsEmpty(TreeWalkListener listener, ListenerErrorType errorType,
+            YangConstructType yangConstructType, String parsableDataTypeName,
+            ListenerErrorLocation errorLocation) {
+
+        if (!listener.getParsedDataStack().empty()) {
+            /*
+             * If stack is empty it indicates error condition, value of
+             * parsableDataTypeName will be null in case there is no name
+             * attached to parsable data type.
+             */
+            String message = constructListenerErrorMessage(errorType, yangConstructType, parsableDataTypeName,
+                    errorLocation);
+            throw new ParserException(message);
+        }
+    }
+
+    /**
+     * Returns parent node config value, if top node does not specify a config
+     * statement then default value true is returned.
+     *
+     * @param listener listener's object
+     * @return true/false parent's config value
+     */
+    public static boolean getParentNodeConfig(TreeWalkListener listener) {
+        Parsable curData = listener.getParsedDataStack().peek();
+        YangNode parentNode = ((YangNode) curData).getParent();
+        if (curData instanceof YangConfig) {
+            return ((YangConfig) curData).isConfig();
+        } else if (curData instanceof YangRpc || curData instanceof YangOutput
+                || curData instanceof YangInput || curData instanceof YangNotification) {
+            return false;
+        } else if (curData instanceof YangCase && parentNode instanceof YangChoice) {
+            return ((YangChoice) parentNode).isConfig();
+        } else {
+            return true;
+        }
+    }
+
+    /**
+     * Checks if a rule occurrences is as per the expected YANG grammar's
+     * cardinality.
+     *
+     * @param childContext child's context
+     * @param yangChildConstruct child construct for whom cardinality is to be
+     *            validated
+     * @param yangParentConstruct parent construct
+     * @param parentName parent name
+     * @throws ParserException exception if cardinality check fails
+     */
+    public static void validateCardinalityMaxOne(List<?> childContext, YangConstructType yangChildConstruct,
+            YangConstructType yangParentConstruct, String parentName)
+            throws ParserException {
+
+        if (!childContext.isEmpty() && childContext.size() != 1) {
+            ParserException parserException = new ParserException("YANG file error: \""
+                    + getYangConstructType(yangChildConstruct) + "\" is defined more than once in \""
+                    + getYangConstructType(yangParentConstruct) + " " + parentName + "\".");
+
+            Iterator<?> context = childContext.iterator();
+            parserException.setLine(((ParserRuleContext) context.next()).getStart().getLine());
+            parserException.setCharPosition(((ParserRuleContext) context.next()).getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks if a rule occurrences is exactly 1.
+     *
+     * @param childContext child's context
+     * @param yangChildConstruct child construct for whom cardinality is to be
+     *                           validated
+     * @param yangParentConstruct parent construct
+     * @param parentName parent name
+     * @param parentContext parents's context
+     * @throws ParserException exception if cardinality check fails
+     */
+    public static void validateCardinalityEqualsOne(List<?> childContext, YangConstructType yangChildConstruct,
+            YangConstructType yangParentConstruct, String parentName,
+            ParserRuleContext parentContext)
+            throws ParserException {
+
+        if (childContext.isEmpty()) {
+            ParserException parserException = new ParserException("YANG file error: Missing \""
+                    + getYangConstructType(yangChildConstruct) + "\" in \"" + getYangConstructType(yangParentConstruct)
+                    + " " + parentName + "\".");
+            parserException.setLine(parentContext.getStart().getLine());
+            parserException.setCharPosition(parentContext.getStart().getCharPositionInLine());
+            throw parserException;
+        } else if (!childContext.isEmpty() && childContext.size() != 1) {
+            Iterator<?> childcontext = childContext.iterator();
+            ParserException parserException = new ParserException("YANG file error: \""
+                    + getYangConstructType(yangChildConstruct) + "\" is present more than once in \""
+                    + getYangConstructType(yangParentConstruct) + " " + parentName + "\".");
+            parserException.setLine(((ParserRuleContext) childcontext.next()).getStart().getLine());
+            parserException.setCharPosition(((ParserRuleContext) childcontext.next()).getStart()
+                    .getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks if a rule occurrences is minimum 1.
+     *
+     * @param childContext child's context
+     * @param yangChildConstruct child construct for whom cardinality is to be
+     *                           validated
+     * @param yangParentConstruct parent construct
+     * @param parentName parent name
+     * @param parentContext parents's context
+     * @throws ParserException exception if cardinality check fails
+     */
+    public static void validateCardinalityNonZero(List<?> childContext, YangConstructType yangChildConstruct,
+            YangConstructType yangParentConstruct, String parentName,
+            ParserRuleContext parentContext)
+            throws ParserException {
+
+        if (childContext.isEmpty()) {
+            ParserException parserException = new ParserException("YANG file error: Missing \""
+                    + getYangConstructType(yangChildConstruct) + "\" in \"" + getYangConstructType(yangParentConstruct)
+                    + " " + parentName + "\".");
+
+            parserException.setLine(parentContext.getStart().getLine());
+            parserException.setCharPosition(parentContext.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+
+    /**
+     * Checks if a either of one construct occurrence.
+     *
+     * @param child1Context       first optional child's context
+     * @param yangChild1Construct first child construct for whom cardinality is
+     *                            to be validated
+     * @param child2Context       second optional child's context
+     * @param yangChild2Construct second child construct for whom cardinality is
+     *                            to be validated
+     * @param yangParentConstruct parent construct
+     * @param parentName          parent name
+     * @param parentContext       parents's context
+     * @throws ParserException exception if cardinality check fails
+     */
+    public static void validateCardinalityEitherOne(List<?> child1Context, YangConstructType yangChild1Construct,
+                                                    List<?> child2Context, YangConstructType yangChild2Construct,
+                                                    YangConstructType yangParentConstruct, String parentName,
+                                                    ParserRuleContext parentContext)
+            throws ParserException {
+
+        if (child1Context.isEmpty() && child2Context.isEmpty()) {
+            ParserException parserException = new ParserException("YANG file error: Either \""
+                    + getYangConstructType(yangChild1Construct) + "\" or \"" + getYangConstructType(yangChild2Construct)
+                    + "\" should be present in \"" + getYangConstructType(yangParentConstruct) + " "
+                    + parentName + "\".");
+            parserException.setLine(parentContext.getStart().getLine());
+            parserException.setCharPosition(parentContext.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
+}
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ParseTreeErrorListener.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ParseTreeErrorListener.java
new file mode 100644
index 0000000..af81d6f
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ParseTreeErrorListener.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.parser.impl.parserutils;
+
+import org.antlr.v4.runtime.BaseErrorListener;
+import org.antlr.v4.runtime.RecognitionException;
+import org.antlr.v4.runtime.Recognizer;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+
+/**
+ * Represent the parse tree error listener.
+ * By default, ANTLR sends all errors to standard error, this is changed by
+ * providing this new implementation of interface ANTLRErrorListener. The
+ * interface has a syntaxError() method that applies to both lexer and parser.
+ */
+public class ParseTreeErrorListener extends BaseErrorListener {
+
+    @Override
+    public void syntaxError(Recognizer<?, ?> recognizer, Object offendingSymbol, int line, int charPositionInLine,
+            String msg, RecognitionException e) {
+
+        ParserException parserException = new ParserException(msg);
+        parserException.setLine(line);
+        parserException.setCharPosition(charPositionInLine);
+        throw parserException;
+    }
+}
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/package-info.java
new file mode 100644
index 0000000..9eafb00
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Provide common utils for parser implementation.
+ */
+package org.onosproject.yangutils.parser.impl.parserutils;
\ No newline at end of file
diff --git a/parser/src/main/java/org/onosproject/yangutils/parser/package-info.java b/parser/src/main/java/org/onosproject/yangutils/parser/package-info.java
new file mode 100644
index 0000000..f039e68
--- /dev/null
+++ b/parser/src/main/java/org/onosproject/yangutils/parser/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+/**
+ * Interfaces to process YANG information from ANTLR generated listeners.
+ */
+package org.onosproject.yangutils.parser;
diff --git a/parser/src/main/resources/CopyrightHeader.txt b/parser/src/main/resources/CopyrightHeader.txt
new file mode 100644
index 0000000..2cbed45
--- /dev/null
+++ b/parser/src/main/resources/CopyrightHeader.txt
@@ -0,0 +1,14 @@
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
diff --git a/parser/src/main/resources/GeneratedYang.g4 b/parser/src/main/resources/GeneratedYang.g4
new file mode 100644
index 0000000..0362cb0
--- /dev/null
+++ b/parser/src/main/resources/GeneratedYang.g4
@@ -0,0 +1,1347 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This is a YANG grammar for parser based on which ANTLR will generate YANG parser.
+ */
+
+grammar GeneratedYang;
+import YangLexer;
+
+@header {
+package org.onosproject.yangutils.parser.antlrgencode;
+}
+
+    yangfile : moduleStatement EOF
+             | subModuleStatement EOF;
+
+    /**
+     * module-stmt         = optsep module-keyword sep identifier-arg-str
+     *                       optsep
+     *                       "{" stmtsep
+     *                           module-header-stmts
+     *                           linkage-stmts
+     *                           meta-stmts
+     *                           revision-stmts
+     *                           body-stmts
+     *                       "}" optsep
+     */
+
+    moduleStatement : MODULE_KEYWORD identifier LEFT_CURLY_BRACE moduleBody RIGHT_CURLY_BRACE;
+
+    moduleBody : moduleHeaderStatement linkageStatements metaStatements revisionStatements bodyStatements;
+
+    /**
+     * module-header-stmts = ;; these stmts can appear in any order
+     *                       [yang-version-stmt stmtsep]
+     *                        namespace-stmt stmtsep
+     *                        prefix-stmt stmtsep
+     */
+
+    moduleHeaderStatement : yangVersionStatement? namespaceStatement prefixStatement
+                            | yangVersionStatement? prefixStatement namespaceStatement
+                            | namespaceStatement yangVersionStatement? prefixStatement
+                            | namespaceStatement prefixStatement yangVersionStatement?
+                            | prefixStatement namespaceStatement yangVersionStatement?
+                            | prefixStatement yangVersionStatement? namespaceStatement
+                            ;
+
+    /**
+     * linkage-stmts       = ;; these stmts can appear in any order
+     *                       *(import-stmt stmtsep)
+     *                       *(include-stmt stmtsep)
+     */
+    linkageStatements : (importStatement
+                  | includeStatement)*;
+
+    /**
+     * meta-stmts          = ;; these stmts can appear in any order
+     *                       [organization-stmt stmtsep]
+     *                       [contact-stmt stmtsep]
+     *                       [description-stmt stmtsep]
+     *                       [reference-stmt stmtsep]
+     */
+    metaStatements : organizationStatement? contactStatement? descriptionStatement? referenceStatement?
+               | organizationStatement? contactStatement? referenceStatement? descriptionStatement?
+               | organizationStatement? descriptionStatement? contactStatement? referenceStatement?
+               | organizationStatement? descriptionStatement? referenceStatement? contactStatement?
+               | organizationStatement? referenceStatement? contactStatement? descriptionStatement?
+               | organizationStatement? referenceStatement? descriptionStatement? contactStatement?
+               | contactStatement? organizationStatement? descriptionStatement? referenceStatement?
+               | contactStatement? organizationStatement? referenceStatement? descriptionStatement?
+               | contactStatement? referenceStatement? organizationStatement? descriptionStatement?
+               | contactStatement? referenceStatement? descriptionStatement? organizationStatement?
+               | contactStatement? descriptionStatement? referenceStatement? organizationStatement?
+               | contactStatement? descriptionStatement? organizationStatement? referenceStatement?
+               | referenceStatement? contactStatement? organizationStatement? descriptionStatement?
+               | referenceStatement? contactStatement? descriptionStatement? organizationStatement?
+               | referenceStatement? organizationStatement? contactStatement? descriptionStatement?
+               | referenceStatement? organizationStatement? descriptionStatement? contactStatement?
+               | referenceStatement? descriptionStatement? organizationStatement? contactStatement?
+               | referenceStatement? descriptionStatement? contactStatement? organizationStatement?
+               | descriptionStatement? referenceStatement? contactStatement? organizationStatement?
+               | descriptionStatement? referenceStatement? organizationStatement? contactStatement?
+               | descriptionStatement? contactStatement? referenceStatement? organizationStatement?
+               | descriptionStatement? contactStatement? organizationStatement? referenceStatement?
+               | descriptionStatement? organizationStatement? contactStatement? referenceStatement?
+               | descriptionStatement? organizationStatement? referenceStatement? contactStatement?
+               ;
+
+    // revision-stmts      = *(revision-stmt stmtsep)
+    revisionStatements : revisionStatement*;
+
+    /**
+     * body-stmts          = *((extension-stmt /
+     *                          feature-stmt /
+     *                          identity-stmt /
+     *                          typedef-stmt /
+     *                          grouping-stmt /
+     *                          data-def-stmt /
+     *                          augment-stmt /
+     *                          rpc-stmt /
+     *                          notification-stmt /
+     *                          deviation-stmt) stmtsep)
+     */
+    bodyStatements : (extensionStatement
+               | featureStatement
+               | identityStatement
+               | typedefStatement
+               | groupingStatement
+               | dataDefStatement
+               | augmentStatement
+               | rpcStatement
+               | notificationStatement
+               | deviationStatement
+               | compilerAnnotationStatement)*
+               ;
+
+    /**
+     * yang-version-stmt   = yang-version-keyword sep yang-version-arg-str
+     *                       optsep stmtend
+     */
+    yangVersionStatement :   YANG_VERSION_KEYWORD version STMTEND;
+
+
+    /**
+     * namespace-stmt      = namespace-keyword sep uri-str optsep stmtend
+     * For namespace validation TODO in Listener
+     */
+    namespaceStatement : NAMESPACE_KEYWORD string STMTEND;
+
+    /**
+     * prefix-stmt         = prefix-keyword sep prefix-arg-str
+     *                       optsep stmtend
+     */
+    prefixStatement : PREFIX_KEYWORD identifier STMTEND;
+
+    /**
+     * import-stmt         = import-keyword sep identifier-arg-str optsep
+     *                       "{" stmtsep
+     *                           prefix-stmt stmtsep
+     *                           [revision-date-stmt stmtsep]
+     *                        "}"
+     */
+    importStatement : IMPORT_KEYWORD identifier LEFT_CURLY_BRACE importStatementBody RIGHT_CURLY_BRACE;
+
+    importStatementBody : prefixStatement revisionDateStatement?;
+
+    // revision-date-stmt = revision-date-keyword sep revision-date stmtend
+    revisionDateStatement : REVISION_DATE_KEYWORD dateArgumentString STMTEND;
+
+    /**
+     * include-stmt        = include-keyword sep identifier-arg-str optsep
+     *                             (";" /
+     *                              "{" stmtsep
+     *                                  [revision-date-stmt stmtsep]
+     *                            "}")
+     */
+    includeStatement : INCLUDE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE revisionDateStatement? RIGHT_CURLY_BRACE);
+
+    /**
+     * organization-stmt   = organization-keyword sep string
+     *                            optsep stmtend
+     */
+    organizationStatement : ORGANIZATION_KEYWORD string STMTEND;
+
+    // contact-stmt        = contact-keyword sep string optsep stmtend
+    contactStatement : CONTACT_KEYWORD string STMTEND;
+
+    // description-stmt    = description-keyword sep string optsep stmtend
+    descriptionStatement : DESCRIPTION_KEYWORD string STMTEND;
+
+    // reference-stmt      = reference-keyword sep string optsep stmtend
+    referenceStatement : REFERENCE_KEYWORD string STMTEND;
+
+    /**
+     * revision-stmt       = revision-keyword sep revision-date optsep
+     *                             (";" /
+     *                              "{" stmtsep
+     *                                  [description-stmt stmtsep]
+     *                                  [reference-stmt stmtsep]
+     *                              "}")
+     */
+    revisionStatement : REVISION_KEYWORD dateArgumentString (STMTEND | LEFT_CURLY_BRACE revisionStatementBody RIGHT_CURLY_BRACE);
+    revisionStatementBody : descriptionStatement? referenceStatement?;
+
+    /**
+     * submodule-stmt      = optsep submodule-keyword sep identifier-arg-str
+     *                             optsep
+     *                             "{" stmtsep
+     *                                 submodule-header-stmts
+     *                                 linkage-stmts
+     *                                 meta-stmts
+     *                                 revision-stmts
+     *                                 body-stmts
+     *                             "}" optsep
+     */
+    subModuleStatement : SUBMODULE_KEYWORD identifier LEFT_CURLY_BRACE submoduleBody RIGHT_CURLY_BRACE;
+    submoduleBody : submoduleHeaderStatement linkageStatements metaStatements revisionStatements bodyStatements;
+
+    /** submodule-header-stmts =
+     *                            ;; these stmts can appear in any order
+     *                            [yang-version-stmt stmtsep]
+     *                             belongs-to-stmt stmtsep
+     */
+    submoduleHeaderStatement : yangVersionStatement? belongstoStatement
+                               | belongstoStatement yangVersionStatement?
+                              ;
+
+    /**
+     * belongs-to-stmt     = belongs-to-keyword sep identifier-arg-str
+     *                       optsep
+     *                       "{" stmtsep
+     *                           prefix-stmt stmtsep
+     *                       "}"
+     */
+    belongstoStatement : BELONGS_TO_KEYWORD identifier LEFT_CURLY_BRACE belongstoStatementBody RIGHT_CURLY_BRACE;
+    belongstoStatementBody : prefixStatement;
+
+    /**
+     * extension-stmt      = extension-keyword sep identifier-arg-str optsep
+     *                       (";" /
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [argument-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                        "}")
+     */
+    extensionStatement : EXTENSION_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE extensionBody RIGHT_CURLY_BRACE);
+    extensionBody : argumentStatement? statusStatement? descriptionStatement? referenceStatement?
+                   | argumentStatement? statusStatement? referenceStatement? descriptionStatement?
+                   | argumentStatement? descriptionStatement? statusStatement? referenceStatement?
+                   | argumentStatement? descriptionStatement? referenceStatement? statusStatement?
+                   | argumentStatement? referenceStatement? descriptionStatement? statusStatement?
+                   | argumentStatement? referenceStatement? statusStatement? descriptionStatement?
+                   | statusStatement? referenceStatement? argumentStatement? descriptionStatement?
+                   | statusStatement? referenceStatement? descriptionStatement? argumentStatement?
+                   | statusStatement? descriptionStatement? referenceStatement? argumentStatement?
+                   | statusStatement? descriptionStatement? argumentStatement? referenceStatement?
+                   | statusStatement? argumentStatement? referenceStatement? descriptionStatement?
+                   | statusStatement? argumentStatement? descriptionStatement? referenceStatement?
+                   | descriptionStatement? argumentStatement? statusStatement? referenceStatement?
+                   | descriptionStatement? argumentStatement? referenceStatement? statusStatement?
+                   | descriptionStatement? statusStatement? argumentStatement? referenceStatement?
+                   | descriptionStatement? statusStatement? referenceStatement? argumentStatement?
+                   | descriptionStatement? referenceStatement? statusStatement? argumentStatement?
+                   | descriptionStatement? referenceStatement? argumentStatement? statusStatement?
+                   | referenceStatement? descriptionStatement? argumentStatement? statusStatement?
+                   | referenceStatement? descriptionStatement? statusStatement? argumentStatement?
+                   | referenceStatement? statusStatement? argumentStatement? descriptionStatement?
+                   | referenceStatement? statusStatement? descriptionStatement? argumentStatement?
+                   | referenceStatement? argumentStatement? descriptionStatement? statusStatement?
+                   | referenceStatement? argumentStatement? statusStatement? descriptionStatement?
+                   ;
+
+    /**
+     * argument-stmt       = argument-keyword sep identifier-arg-str optsep
+     *                       (";" /
+     *                        "{" stmtsep
+     *                            [yin-element-stmt stmtsep]
+     *                        "}")
+     */
+    argumentStatement : ARGUMENT_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE argumentBody RIGHT_CURLY_BRACE);
+    argumentBody : yinElementStatement?;
+
+    /**
+     * yin-element-stmt    = yin-element-keyword sep yin-element-arg-str
+     *                       stmtend
+     */
+    yinElementStatement : YIN_ELEMENT_KEYWORD (TRUE_KEYWORD | FALSE_KEYWORD) STMTEND;
+
+    /**
+     * identity-stmt       = identity-keyword sep identifier-arg-str optsep
+     *                       (";" /
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [base-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                        "}")
+     */
+    identityStatement : IDENTITY_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE identityBody RIGHT_CURLY_BRACE);
+    identityBody : baseStatement? statusStatement? descriptionStatement? referenceStatement?
+                  | baseStatement? statusStatement? referenceStatement? descriptionStatement?
+                  | baseStatement? descriptionStatement? statusStatement? referenceStatement?
+                  | baseStatement? descriptionStatement? referenceStatement? statusStatement?
+                  | baseStatement? referenceStatement? descriptionStatement? statusStatement?
+                  | baseStatement? referenceStatement? statusStatement? descriptionStatement?
+                  | referenceStatement? baseStatement? statusStatement? descriptionStatement?
+                  | referenceStatement? baseStatement? descriptionStatement? statusStatement?
+                  | referenceStatement? statusStatement? baseStatement? descriptionStatement?
+                  | referenceStatement? statusStatement? descriptionStatement? baseStatement?
+                  | referenceStatement? descriptionStatement? statusStatement? baseStatement?
+                  | referenceStatement? descriptionStatement? baseStatement? statusStatement?
+                  | descriptionStatement? referenceStatement? statusStatement? baseStatement?
+                  | descriptionStatement? referenceStatement? statusStatement? baseStatement?
+                  | descriptionStatement? referenceStatement? baseStatement? statusStatement?
+                  | descriptionStatement? statusStatement? baseStatement? referenceStatement?
+                  | descriptionStatement? statusStatement? referenceStatement? baseStatement?
+                  | descriptionStatement? baseStatement? referenceStatement? statusStatement?
+                  | descriptionStatement? baseStatement? statusStatement? referenceStatement?
+                  | statusStatement? baseStatement? descriptionStatement? referenceStatement?
+                  | statusStatement? baseStatement? referenceStatement? descriptionStatement?
+                  | statusStatement? descriptionStatement? baseStatement? referenceStatement?
+                  | statusStatement? descriptionStatement? referenceStatement? baseStatement?
+                  | statusStatement? referenceStatement? descriptionStatement? baseStatement?
+                  | statusStatement? referenceStatement? baseStatement? descriptionStatement?
+                  ;
+
+    /**
+     * base-stmt           = base-keyword sep identifier-ref-arg-str
+     *                          optsep stmtend*
+     * identifier-ref-arg  = [prefix ":"] identifier
+     */
+    baseStatement : BASE_KEYWORD string STMTEND;
+
+    /**
+     *  feature-stmt        = feature-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             *(if-feature-stmt stmtsep)
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                         "}")
+     */
+    featureStatement : FEATURE_KEYWORD string (STMTEND | LEFT_CURLY_BRACE featureBody RIGHT_CURLY_BRACE);
+    featureBody : ifFeatureStatement* statusStatement? descriptionStatement? referenceStatement?
+                 | ifFeatureStatement* statusStatement? referenceStatement? descriptionStatement?
+                 | ifFeatureStatement* descriptionStatement? statusStatement? referenceStatement?
+                 | ifFeatureStatement* descriptionStatement? referenceStatement? statusStatement?
+                 | ifFeatureStatement* referenceStatement? statusStatement? descriptionStatement?
+                 | ifFeatureStatement* referenceStatement? descriptionStatement? statusStatement?
+                 | statusStatement? ifFeatureStatement* descriptionStatement? referenceStatement?
+                 | statusStatement? ifFeatureStatement* referenceStatement? descriptionStatement?
+                 | statusStatement? descriptionStatement? ifFeatureStatement* referenceStatement?
+                 | statusStatement? descriptionStatement? referenceStatement? ifFeatureStatement*
+                 | statusStatement? referenceStatement? ifFeatureStatement* descriptionStatement?
+                 | statusStatement? referenceStatement? descriptionStatement? ifFeatureStatement*
+                 | descriptionStatement? ifFeatureStatement* statusStatement? referenceStatement?
+                 | descriptionStatement? ifFeatureStatement* referenceStatement? statusStatement?
+                 | descriptionStatement? statusStatement? ifFeatureStatement* referenceStatement?
+                 | descriptionStatement? statusStatement? referenceStatement? ifFeatureStatement*
+                 | descriptionStatement? referenceStatement* statusStatement? ifFeatureStatement*
+                 | descriptionStatement? referenceStatement* ifFeatureStatement? statusStatement?
+                 | referenceStatement? ifFeatureStatement* statusStatement? descriptionStatement?
+                 | referenceStatement? ifFeatureStatement* descriptionStatement? statusStatement?
+                 | referenceStatement? descriptionStatement? statusStatement? ifFeatureStatement*
+                 | referenceStatement? descriptionStatement? ifFeatureStatement* statusStatement?
+                 | referenceStatement? statusStatement? descriptionStatement? ifFeatureStatement*
+                 | referenceStatement? statusStatement? ifFeatureStatement* descriptionStatement?
+                 ;
+
+    /**
+     *  data-def-stmt       = container-stmt /
+     *                       leaf-stmt /
+     *                       leaf-list-stmt /
+     *                       list-stmt /
+     *                       choice-stmt /
+     *                       anyxml-stmt /
+     *                       uses-stmt
+     */
+    dataDefStatement : containerStatement
+                    | leafStatement
+                    | leafListStatement
+                    | listStatement
+                    | choiceStatement
+                    | anyxmlStatement
+                    | usesStatement;
+
+    /**
+     *  if-feature-stmt     = if-feature-keyword sep identifier-ref-arg-str
+     *                        optsep stmtend
+     */
+    ifFeatureStatement : IF_FEATURE_KEYWORD string STMTEND;
+
+    /**
+    *    units-stmt          = units-keyword sep string optsep stmtend
+    */
+    unitsStatement : UNITS_KEYWORD string STMTEND;
+
+    /**
+     *   typedef-stmt        = typedef-keyword sep identifier-arg-str optsep
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             type-stmt stmtsep
+     *                            [units-stmt stmtsep]
+     *                             [default-stmt stmtsep]
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                           "}"
+     * TODO : 0..1 occurance to be validated in listener
+     */
+    typedefStatement : TYPEDEF_KEYWORD identifier LEFT_CURLY_BRACE
+                   (typeStatement | unitsStatement | defaultStatement | statusStatement | descriptionStatement | referenceStatement)*
+                   RIGHT_CURLY_BRACE;
+
+    /**
+     *  type-stmt           = type-keyword sep identifier-ref-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                            type-body-stmts
+     *                         "}")
+     */
+    typeStatement : TYPE_KEYWORD string (STMTEND | LEFT_CURLY_BRACE typeBodyStatements RIGHT_CURLY_BRACE);
+
+    /**
+     *  type-body-stmts     = numerical-restrictions /
+     *                        decimal64-specification /
+     *                       string-restrictions /
+     *                        enum-specification /
+     *                        leafref-specification /
+     *                        identityref-specification /
+     *                        instance-identifier-specification /
+     *                        bits-specification /
+     *                        union-specification
+     *
+     */
+    typeBodyStatements : numericalRestrictions | decimal64Specification | stringRestrictions | enumSpecification
+                    | leafrefSpecification | identityrefSpecification | instanceIdentifierSpecification
+                    | bitsSpecification | unionSpecification;
+
+    /**
+     *    decimal64-specification = ;; these stmts can appear in any order
+     *                               fraction-digits-stmt
+     *                               [range-stmt]
+     */
+     decimal64Specification : fractionDigitStatement rangeStatement?;
+
+    /**
+     *  fraction-digits-stmt = fraction-digits-keyword sep
+     *                         fraction-digits-arg-str stmtend
+     *
+     *  fraction-digits-arg-str = < a string that matches the rule
+     *                             fraction-digits-arg >
+     *
+     *  fraction-digits-arg = ("1" ["0" / "1" / "2" / "3" / "4" /
+     *                              "5" / "6" / "7" / "8"])
+     *                        / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
+     */
+    fractionDigitStatement : FRACTION_DIGITS_KEYWORD fraction STMTEND;
+
+    /**
+     *  numerical-restrictions = range-stmt stmtsep
+     */
+    numericalRestrictions : rangeStatement;
+
+    /**
+     *  range-stmt          = range-keyword sep range-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [error-message-stmt stmtsep]
+     *                             [error-app-tag-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+    rangeStatement : RANGE_KEYWORD range (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+
+    commonStatements : errorMessageStatement? errorAppTagStatement? descriptionStatement? referenceStatement?
+                 | errorMessageStatement? errorAppTagStatement? referenceStatement? descriptionStatement?
+                 | errorMessageStatement? descriptionStatement? errorAppTagStatement? referenceStatement?
+                 | errorMessageStatement? descriptionStatement? referenceStatement? errorAppTagStatement?
+                 | errorMessageStatement? referenceStatement? errorAppTagStatement? descriptionStatement?
+                 | errorMessageStatement? referenceStatement? descriptionStatement? errorAppTagStatement?
+                 | errorAppTagStatement? errorMessageStatement? descriptionStatement? referenceStatement?
+                 | errorAppTagStatement? errorMessageStatement? referenceStatement? descriptionStatement?
+                 | errorAppTagStatement? descriptionStatement? descriptionStatement? errorMessageStatement?
+                 | errorAppTagStatement? descriptionStatement? errorMessageStatement? descriptionStatement?
+                 | errorAppTagStatement? referenceStatement? errorMessageStatement? descriptionStatement?
+                 | errorAppTagStatement? referenceStatement? descriptionStatement? errorMessageStatement?
+                 | descriptionStatement? errorMessageStatement? errorAppTagStatement? referenceStatement?
+                 | descriptionStatement? errorMessageStatement? referenceStatement? errorAppTagStatement?
+                 | descriptionStatement? errorAppTagStatement? errorMessageStatement? referenceStatement?
+                 | descriptionStatement? errorAppTagStatement? referenceStatement? errorMessageStatement?
+                 | descriptionStatement? referenceStatement? errorMessageStatement? errorAppTagStatement?
+                 | descriptionStatement? referenceStatement? errorAppTagStatement? errorMessageStatement?
+                 | referenceStatement? errorMessageStatement? descriptionStatement? errorAppTagStatement?
+                 | referenceStatement? errorMessageStatement? errorAppTagStatement? descriptionStatement?
+                 | referenceStatement? errorAppTagStatement? descriptionStatement? errorMessageStatement?
+                 | referenceStatement? errorAppTagStatement? errorMessageStatement? descriptionStatement?
+                 | referenceStatement? descriptionStatement? errorMessageStatement? errorAppTagStatement?
+                 | referenceStatement? descriptionStatement? errorAppTagStatement? errorMessageStatement?
+                 ;
+
+    /**
+     *  string-restrictions = ;; these stmts can appear in any order
+     *                        [length-stmt stmtsep]
+     *                        *(pattern-stmt stmtsep)
+     */
+    stringRestrictions : ((lengthStatement)? (patternStatement)*) | ((patternStatement)* (lengthStatement)?);
+
+    /**
+     *  length-stmt         = length-keyword sep length-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [error-message-stmt stmtsep]
+     *                             [error-app-tag-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+    lengthStatement : LENGTH_KEYWORD length
+                  (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+
+    /**
+     *  pattern-stmt        = pattern-keyword sep string optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [error-message-stmt stmtsep]
+     *                             [error-app-tag-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+    patternStatement : PATTERN_KEYWORD string (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+
+    /**
+     *  default-stmt        = default-keyword sep string stmtend
+     */
+    defaultStatement : DEFAULT_KEYWORD string STMTEND;
+
+    /**
+     *  enum-specification  = 1*(enum-stmt stmtsep)
+     */
+    enumSpecification : enumStatement+;
+
+    /**
+     *  enum-stmt           = enum-keyword sep string optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [value-stmt stmtsep]
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+    enumStatement : ENUM_KEYWORD string (STMTEND | LEFT_CURLY_BRACE enumStatementBody RIGHT_CURLY_BRACE);
+
+    enumStatementBody : valueStatement? statusStatement? descriptionStatement? referenceStatement?
+                   | valueStatement? statusStatement? referenceStatement? descriptionStatement?
+                   | valueStatement? descriptionStatement? statusStatement? referenceStatement?
+                   | valueStatement? descriptionStatement? referenceStatement? statusStatement?
+                   | valueStatement? referenceStatement? statusStatement? descriptionStatement?
+                   | valueStatement? referenceStatement? descriptionStatement? statusStatement?
+                   | statusStatement? valueStatement? descriptionStatement? referenceStatement?
+                   | statusStatement? valueStatement? referenceStatement? descriptionStatement?
+                   | statusStatement? descriptionStatement? descriptionStatement? valueStatement?
+                   | statusStatement? descriptionStatement? valueStatement? descriptionStatement?
+                   | statusStatement? referenceStatement? valueStatement? descriptionStatement?
+                   | statusStatement? referenceStatement? descriptionStatement? valueStatement?
+                   | descriptionStatement? valueStatement? statusStatement? referenceStatement?
+                   | descriptionStatement? valueStatement? referenceStatement? statusStatement?
+                   | descriptionStatement? statusStatement? valueStatement? referenceStatement?
+                   | descriptionStatement? statusStatement? referenceStatement? valueStatement?
+                   | descriptionStatement? referenceStatement? valueStatement? statusStatement?
+                   | descriptionStatement? referenceStatement? statusStatement? valueStatement?
+                   | referenceStatement? valueStatement? descriptionStatement? statusStatement?
+                   | referenceStatement? valueStatement? statusStatement? descriptionStatement?
+                   | referenceStatement? statusStatement? descriptionStatement? valueStatement?
+                   | referenceStatement? statusStatement? valueStatement? descriptionStatement?
+                   | referenceStatement? descriptionStatement? valueStatement? statusStatement?
+                   | referenceStatement? descriptionStatement? statusStatement? valueStatement?
+                   ;
+
+    /**
+     *  leafref-specification =
+     *                        ;; these stmts can appear in any order
+     *                        path-stmt stmtsep
+     *                        [require-instance-stmt stmtsep]
+     */
+    leafrefSpecification : (pathStatement (requireInstanceStatement)?) | ((requireInstanceStatement)? pathStatement);
+
+    /**
+     *  path-stmt           = path-keyword sep path-arg-str stmtend
+     */
+    pathStatement : PATH_KEYWORD path STMTEND;
+
+    /**
+     *  require-instance-stmt = require-instance-keyword sep
+     *                           require-instance-arg-str stmtend
+     *  require-instance-arg-str = < a string that matches the rule
+     *                             require-instance-arg >
+     *  require-instance-arg = true-keyword / false-keyword
+     */
+    requireInstanceStatement : REQUIRE_INSTANCE_KEYWORD requireInstance STMTEND;
+
+    /**
+     *  instance-identifier-specification =
+     *                        [require-instance-stmt stmtsep]
+     */
+    instanceIdentifierSpecification : requireInstanceStatement?;
+
+    /**
+     * identityref-specification =
+     *                        base-stmt stmtsep
+     */
+    identityrefSpecification : baseStatement;
+
+    /**
+     *  union-specification = 1*(type-stmt stmtsep)
+     */
+    unionSpecification : typeStatement+;
+
+    /**
+     *  bits-specification  = 1*(bit-stmt stmtsep)
+     */
+    bitsSpecification : bitStatement+;
+
+    /**
+     * bit-stmt            = bit-keyword sep identifier-arg-str optsep
+     *                       (";" /
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [position-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                          "}"
+     *                        "}")
+     */
+    bitStatement : BIT_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE bitBodyStatement RIGHT_CURLY_BRACE);
+
+    bitBodyStatement : positionStatement? statusStatement? descriptionStatement? referenceStatement?
+                  | positionStatement? statusStatement? referenceStatement? descriptionStatement?
+                  | positionStatement? descriptionStatement? statusStatement? referenceStatement?
+                  | positionStatement? descriptionStatement? referenceStatement? statusStatement?
+                  | positionStatement? referenceStatement? statusStatement? descriptionStatement?
+                  | positionStatement? referenceStatement? descriptionStatement? statusStatement?
+                  | statusStatement? positionStatement? descriptionStatement? referenceStatement?
+                  | statusStatement? positionStatement? referenceStatement? descriptionStatement?
+                  | statusStatement? descriptionStatement? descriptionStatement? positionStatement?
+                  | statusStatement? descriptionStatement? positionStatement? descriptionStatement?
+                  | statusStatement? referenceStatement? positionStatement? descriptionStatement?
+                  | statusStatement? referenceStatement? descriptionStatement? positionStatement?
+                  | descriptionStatement? positionStatement? statusStatement? referenceStatement?
+                  | descriptionStatement? positionStatement? referenceStatement? statusStatement?
+                  | descriptionStatement? statusStatement? positionStatement? referenceStatement?
+                  | descriptionStatement? statusStatement? referenceStatement? positionStatement?
+                  | descriptionStatement? referenceStatement? positionStatement? statusStatement?
+                  | descriptionStatement? referenceStatement? statusStatement? positionStatement?
+                  | referenceStatement? positionStatement? descriptionStatement? statusStatement?
+                  | referenceStatement? positionStatement? statusStatement? descriptionStatement?
+                  | referenceStatement? statusStatement? descriptionStatement? positionStatement?
+                  | referenceStatement? statusStatement? positionStatement? descriptionStatement?
+                  | referenceStatement? descriptionStatement? positionStatement? statusStatement?
+                  | referenceStatement? descriptionStatement? statusStatement? positionStatement?
+                  ;
+
+    /**
+     *  position-stmt       = position-keyword sep
+     *                        position-value-arg-str stmtend
+     *  position-value-arg-str = < a string that matches the rule
+     *                              position-value-arg >
+     *  position-value-arg  = non-negative-integer-value
+     */
+    positionStatement : POSITION_KEYWORD position STMTEND;
+
+    /**
+     *  status-stmt         = status-keyword sep status-arg-str stmtend
+     *  status-arg-str      = < a string that matches the rule
+     *                         status-arg >
+     *  status-arg          = current-keyword /
+     *                        obsolete-keyword /
+     *                        deprecated-keyword
+     */
+    statusStatement : STATUS_KEYWORD status STMTEND;
+
+    /**
+     *  config-stmt         = config-keyword sep
+     *                        config-arg-str stmtend
+     *  config-arg-str      = < a string that matches the rule
+     *                          config-arg >
+     *  config-arg          = true-keyword / false-keyword
+     */
+    configStatement : CONFIG_KEYWORD config STMTEND;
+
+    /**
+     *  mandatory-stmt      = mandatory-keyword sep
+     *                        mandatory-arg-str stmtend
+     *
+     *  mandatory-arg-str   = < a string that matches the rule
+     *                          mandatory-arg >
+     *
+     *  mandatory-arg       = true-keyword / false-keyword
+     */
+    mandatoryStatement : MANDATORY_KEYWORD mandatory STMTEND;
+
+    /**
+     *  presence-stmt       = presence-keyword sep string stmtend
+     */
+    presenceStatement : PRESENCE_KEYWORD string STMTEND;
+
+    /**
+     *  ordered-by-stmt     = ordered-by-keyword sep
+     *                        ordered-by-arg-str stmtend
+     *
+     *  ordered-by-arg-str  = < a string that matches the rule
+     *                          ordered-by-arg >
+     *
+     *  ordered-by-arg      = user-keyword / system-keyword
+     */
+    orderedByStatement : ORDERED_BY_KEYWORD orderedBy STMTEND;
+
+    /**
+     *  must-stmt           = must-keyword sep string optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [error-message-stmt stmtsep]
+     *                             [error-app-tag-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+    mustStatement : MUST_KEYWORD string (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+
+    /**
+     *   error-message-stmt  = error-message-keyword sep string stmtend
+     */
+    errorMessageStatement : ERROR_MESSAGE_KEYWORD string STMTEND;
+
+    /**
+     *  error-app-tag-stmt  = error-app-tag-keyword sep string stmtend
+     */
+    errorAppTagStatement : ERROR_APP_TAG_KEYWORD string STMTEND;
+
+    /**
+     *  min-elements-stmt   = min-elements-keyword sep
+     *                        min-value-arg-str stmtend
+     *  min-value-arg-str   = < a string that matches the rule
+     *                          min-value-arg >
+     *  min-value-arg       = non-negative-integer-value
+     */
+    minElementsStatement : MIN_ELEMENTS_KEYWORD minValue STMTEND;
+
+    /**
+     *  max-elements-stmt   = max-elements-keyword sep
+     *                        max-value-arg-str stmtend
+     *  max-value-arg-str   = < a string that matches the rule
+     *                          max-value-arg >
+     *  max-value-arg       = unbounded-keyword /
+     *                        positive-integer-value
+     */
+    maxElementsStatement :  MAX_ELEMENTS_KEYWORD maxValue STMTEND;
+
+    /**
+     *  value-stmt          = value-keyword sep integer-value stmtend
+     */
+    valueStatement : VALUE_KEYWORD value STMTEND;
+
+    /**
+     *   grouping-stmt       = grouping-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *((typedef-stmt /
+     *                                grouping-stmt) stmtsep)
+     *                             *(data-def-stmt stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    groupingStatement : GROUPING_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE
+                      (statusStatement | descriptionStatement | referenceStatement | typedefStatement | groupingStatement
+                       | dataDefStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  container-stmt      = container-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [when-stmt stmtsep]
+     *                             *(if-feature-stmt stmtsep)
+     *                             *(must-stmt stmtsep)
+     *                             [presence-stmt stmtsep]
+     *                             [config-stmt stmtsep]
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *((typedef-stmt /
+     *                                grouping-stmt) stmtsep)
+     *                             *(data-def-stmt stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    containerStatement : CONTAINER_KEYWORD identifier
+                     (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | mustStatement | presenceStatement | configStatement
+                     | statusStatement | descriptionStatement | referenceStatement | typedefStatement | groupingStatement
+                     | dataDefStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  leaf-stmt           = leaf-keyword sep identifier-arg-str optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [when-stmt stmtsep]
+     *                            *(if-feature-stmt stmtsep)
+     *                            type-stmt stmtsep
+     *                            [units-stmt stmtsep]
+     *                            *(must-stmt stmtsep)
+     *                            [default-stmt stmtsep]
+     *                            [config-stmt stmtsep]
+     *                            [mandatory-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                         "}"
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    leafStatement : LEAF_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | typeStatement | unitsStatement
+              | mustStatement | defaultStatement | configStatement | mandatoryStatement | statusStatement  | descriptionStatement
+              | referenceStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  leaf-list-stmt      = leaf-list-keyword sep identifier-arg-str optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [when-stmt stmtsep]
+     *                            *(if-feature-stmt stmtsep)
+     *                            type-stmt stmtsep
+     *                            [units-stmt stmtsep]
+     *                            *(must-stmt stmtsep)
+     *                            [config-stmt stmtsep]
+     *                            [min-elements-stmt stmtsep]
+     *                            [max-elements-stmt stmtsep]
+     *                            [ordered-by-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                         "}"
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    leafListStatement : LEAF_LIST_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | typeStatement
+                     | unitsStatement | mustStatement | configStatement | minElementsStatement | maxElementsStatement | orderedByStatement
+                     | statusStatement | descriptionStatement | referenceStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  list-stmt           = list-keyword sep identifier-arg-str optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [when-stmt stmtsep]
+     *                            *(if-feature-stmt stmtsep)
+     *                            *(must-stmt stmtsep)
+     *                            [key-stmt stmtsep]
+     *                            *(unique-stmt stmtsep)
+     *                            [config-stmt stmtsep]
+     *                            [min-elements-stmt stmtsep]
+     *                            [max-elements-stmt stmtsep]
+     *                            [ordered-by-stmt stmtsep]
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                            *((typedef-stmt /
+     *                               grouping-stmt) stmtsep)
+     *                            1*(data-def-stmt stmtsep)
+     *                         "}"
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    listStatement : LIST_KEYWORD identifier LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | mustStatement | keyStatement
+              | uniqueStatement | configStatement | minElementsStatement | maxElementsStatement | orderedByStatement | statusStatement
+              | descriptionStatement | referenceStatement | typedefStatement | groupingStatement| dataDefStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  key-stmt            = key-keyword sep key-arg-str stmtend
+     */
+    keyStatement : KEY_KEYWORD key STMTEND;
+
+    /**
+     *  unique-stmt         = unique-keyword sep unique-arg-str stmtend
+     */
+    uniqueStatement: UNIQUE_KEYWORD unique STMTEND;
+
+    /**
+     *  choice-stmt         = choice-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [when-stmt stmtsep]
+     *                             *(if-feature-stmt stmtsep)
+     *                             [default-stmt stmtsep]
+     *                             [config-stmt stmtsep]
+     *                             [mandatory-stmt stmtsep]
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *((short-case-stmt / case-stmt) stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    choiceStatement : CHOICE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | defaultStatement
+                  | configStatement | mandatoryStatement | statusStatement | descriptionStatement | referenceStatement | shortCaseStatement
+                  | caseStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  short-case-stmt     = container-stmt /
+     *                        leaf-stmt /
+     *                        leaf-list-stmt /
+     *                        list-stmt /
+     *                        anyxml-stmt
+     */
+    shortCaseStatement : containerStatement | leafStatement | leafListStatement | listStatement | anyxmlStatement;
+
+    /**
+     *  case-stmt           = case-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [when-stmt stmtsep]
+     *                             *(if-feature-stmt stmtsep)
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *(data-def-stmt stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    caseStatement : CASE_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | statusStatement
+              | descriptionStatement | referenceStatement | dataDefStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *    anyxml-stmt         = anyxml-keyword sep identifier-arg-str optsep
+     *                         (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [when-stmt stmtsep]
+     *                             *(if-feature-stmt stmtsep)
+     *                             *(must-stmt stmtsep)
+     *                             [config-stmt stmtsep]
+     *                             [mandatory-stmt stmtsep]
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     */
+     anyxmlStatement : ANYXML_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement
+                     | mustStatement | configStatement | mandatoryStatement | statusStatement | descriptionStatement
+                     | referenceStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  uses-stmt           = uses-keyword sep identifier-ref-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [when-stmt stmtsep]
+     *                             *(if-feature-stmt stmtsep)
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *(refine-stmt stmtsep)
+     *                             *(uses-augment-stmt stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    usesStatement : USES_KEYWORD string (STMTEND | LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | statusStatement
+                | descriptionStatement | referenceStatement | refineStatement | augmentStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  refine-stmt         = refine-keyword sep refine-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             (refine-container-stmts /
+     *                              refine-leaf-stmts /
+     *                              refine-leaf-list-stmts /
+     *                              refine-list-stmts /
+     *                              refine-choice-stmts /
+     *                              refine-case-stmts /
+     *                              refine-anyxml-stmts)
+     *                         "}")
+     */
+    refineStatement : REFINE_KEYWORD refine (STMTEND  | LEFT_CURLY_BRACE (refineContainerStatements
+                    | refineLeafStatements | refineLeafListStatements | refineListStatements | refineChoiceStatements
+                    | refineCaseStatements | refineAnyxmlStatements) RIGHT_CURLY_BRACE);
+
+    /**
+     *  refine-container-stmts =
+     *                        ;; these stmts can appear in any order
+     *                        *(must-stmt stmtsep)
+     *                        [presence-stmt stmtsep]
+     *                        [config-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                         [reference-stmt stmtsep]
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    refineContainerStatements : (mustStatement | presenceStatement | configStatement | descriptionStatement | referenceStatement)* ;
+
+    /**
+     *   refine-leaf-stmts   = ;; these stmts can appear in any order
+     *                         *(must-stmt stmtsep)
+     *                         [default-stmt stmtsep]
+     *                         [config-stmt stmtsep]
+     *                        [mandatory-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    refineLeafStatements : (mustStatement | defaultStatement | configStatement | mandatoryStatement | descriptionStatement | referenceStatement)*;
+
+    /**
+     *  refine-leaf-list-stmts =
+     *                        ;; these stmts can appear in any order
+     *                        *(must-stmt stmtsep)
+     *                        [config-stmt stmtsep]
+     *                        [min-elements-stmt stmtsep]
+     *                        [max-elements-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    refineLeafListStatements : (mustStatement | configStatement | minElementsStatement | maxElementsStatement | descriptionStatement
+                             | referenceStatement)*;
+
+    /**
+     *  refine-list-stmts   = ;; these stmts can appear in any order
+     *                        *(must-stmt stmtsep)
+     *                        [config-stmt stmtsep]
+     *                        [min-elements-stmt stmtsep]
+     *                        [max-elements-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    refineListStatements : (mustStatement | configStatement | minElementsStatement | maxElementsStatement | descriptionStatement
+                        | referenceStatement)*;
+
+    /**
+     *  refine-choice-stmts = ;; these stmts can appear in any order
+     *                        [default-stmt stmtsep]
+     *                        [config-stmt stmtsep]
+     *                        [mandatory-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    refineChoiceStatements : (defaultStatement | configStatement | mandatoryStatement | descriptionStatement | referenceStatement)*;
+
+    /**
+     *  refine-case-stmts   = ;; these stmts can appear in any order
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     *
+     */
+    refineCaseStatements : (descriptionStatement | referenceStatement)? | (referenceStatement | descriptionStatement)?;
+
+    /**
+     *  refine-anyxml-stmts = ;; these stmts can appear in any order
+     *                        *(must-stmt stmtsep)
+     *                        [config-stmt stmtsep]
+     *                        [mandatory-stmt stmtsep]
+     *                        [description-stmt stmtsep]
+     *                        [reference-stmt stmtsep]
+     */
+     refineAnyxmlStatements : (mustStatement | configStatement | mandatoryStatement | descriptionStatement
+                            | referenceStatement)*;
+
+    /**
+     *  augment-stmt        = augment-keyword sep augment-arg-str optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [when-stmt stmtsep]
+     *                            *(if-feature-stmt stmtsep)
+     *                            [status-stmt stmtsep]
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                            1*((data-def-stmt stmtsep) /
+     *                               (case-stmt stmtsep))
+     *                         "}"
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    augmentStatement : AUGMENT_KEYWORD augment LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | statusStatement
+                   | descriptionStatement | referenceStatement | dataDefStatement  | caseStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  when-stmt           = when-keyword sep string optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                          "}")
+     *
+     */
+    whenStatement : WHEN_KEYWORD string (STMTEND | LEFT_CURLY_BRACE ((descriptionStatement? referenceStatement?)
+                       | (referenceStatement? descriptionStatement?)) RIGHT_CURLY_BRACE);
+
+    /**
+     *  rpc-stmt            = rpc-keyword sep identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             *(if-feature-stmt stmtsep)
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *((typedef-stmt /
+     *                                grouping-stmt) stmtsep)
+     *                             [input-stmt stmtsep]
+     *                             [output-stmt stmtsep]
+     *                         "}")
+     */
+    rpcStatement : RPC_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (ifFeatureStatement | statusStatement | descriptionStatement
+                | referenceStatement | typedefStatement | groupingStatement | inputStatement | outputStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     * input-stmt          = input-keyword optsep
+     *                       "{" stmtsep
+     *                           ;; these stmts can appear in any order
+     *                           *((typedef-stmt /
+     *                              grouping-stmt) stmtsep)
+     *                           1*(data-def-stmt stmtsep)
+     *                         "}"
+     */
+    inputStatement : INPUT_KEYWORD LEFT_CURLY_BRACE (typedefStatement | groupingStatement | dataDefStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  output-stmt         = output-keyword optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            *((typedef-stmt /
+     *                               grouping-stmt) stmtsep)
+     *                            1*(data-def-stmt stmtsep)
+     *                        "}"
+     */
+    outputStatement : OUTPUT_KEYWORD LEFT_CURLY_BRACE (typedefStatement | groupingStatement | dataDefStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     *  notification-stmt   = notification-keyword sep
+     *                        identifier-arg-str optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             ;; these stmts can appear in any order
+     *                             *(if-feature-stmt stmtsep)
+     *                             [status-stmt stmtsep]
+     *                             [description-stmt stmtsep]
+     *                             [reference-stmt stmtsep]
+     *                             *((typedef-stmt /
+     *                                grouping-stmt) stmtsep)
+     *                             *(data-def-stmt stmtsep)
+     *                         "}")
+     * TODO : 0..1 occurance to be checked in listener
+     */
+     notificationStatement : NOTIFICATION_KEYWORD identifier (STMTEND | LEFT_CURLY_BRACE (ifFeatureStatement
+                           | statusStatement | descriptionStatement | referenceStatement | typedefStatement
+                           | groupingStatement | dataDefStatement)* RIGHT_CURLY_BRACE);
+
+    /**
+     *  deviation-stmt      = deviation-keyword sep
+     *                        deviation-arg-str optsep
+     *                        "{" stmtsep
+     *                            ;; these stmts can appear in any order
+     *                            [description-stmt stmtsep]
+     *                            [reference-stmt stmtsep]
+     *                            (deviate-not-supported-stmt /
+     *                              1*(deviate-add-stmt /
+     *                                 deviate-replace-stmt /
+     *                                 deviate-delete-stmt))
+     *                        "}"
+     * TODO : 0..1 occurance to be checked in listener
+     */
+    deviationStatement: DEVIATION_KEYWORD deviation LEFT_CURLY_BRACE (descriptionStatement | referenceStatement
+                      | deviateNotSupportedStatement | deviateAddStatement | deviateReplaceStatement
+                      | deviateDeleteStatement)* RIGHT_CURLY_BRACE;
+
+    /**
+     * deviate-not-supported-stmt =
+     *                       deviate-keyword sep
+     *                       not-supported-keyword optsep
+     *                       (";" /
+     *                        "{" stmtsep
+     *                        "}")
+     */
+    deviateNotSupportedStatement: DEVIATE_KEYWORD NOT_SUPPORTED_KEYWORD (STMTEND | LEFT_CURLY_BRACE RIGHT_CURLY_BRACE);
+
+    /**
+     *  deviate-add-stmt    = deviate-keyword sep add-keyword optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             [units-stmt stmtsep]
+     *                             *(must-stmt stmtsep)
+     *                             *(unique-stmt stmtsep)
+     *                             [default-stmt stmtsep]
+     *                             [config-stmt stmtsep]
+     *                             [mandatory-stmt stmtsep]
+     *                             [min-elements-stmt stmtsep]
+     *                             [max-elements-stmt stmtsep]
+     *                         "}")
+     */
+    deviateAddStatement: DEVIATE_KEYWORD ADD_KEYWORD (STMTEND | (LEFT_CURLY_BRACE unitsStatement? mustStatement* uniqueStatement*
+                      defaultStatement? configStatement? mandatoryStatement? minElementsStatement? maxElementsStatement?
+                      RIGHT_CURLY_BRACE));
+
+    /**
+     *  deviate-delete-stmt = deviate-keyword sep delete-keyword optsep
+     *                        (";" /
+     *                         "{" stmtsep
+     *                             [units-stmt stmtsep]
+     *                             *(must-stmt stmtsep)
+     *                             *(unique-stmt stmtsep)
+     *                               [default-stmt stmtsep]
+     *                           "}")
+     */
+    deviateDeleteStatement: DEVIATE_KEYWORD DELETE_KEYWORD (STMTEND
+                       | (LEFT_CURLY_BRACE  unitsStatement? mustStatement* uniqueStatement* defaultStatement? RIGHT_CURLY_BRACE));
+
+    /**
+     *   deviate-replace-stmt = deviate-keyword sep replace-keyword optsep
+     *                         (";" /
+     *                          "{" stmtsep
+     *                              [type-stmt stmtsep]
+     *                              [units-stmt stmtsep]
+     *                              [default-stmt stmtsep]
+     *                              [config-stmt stmtsep]
+     *                              [mandatory-stmt stmtsep]
+     *                              [min-elements-stmt stmtsep]
+     *                              [max-elements-stmt stmtsep]
+     *                          "}")
+     */
+    deviateReplaceStatement: DEVIATE_KEYWORD REPLACE_KEYWORD (STMTEND | (LEFT_CURLY_BRACE typeStatement? unitsStatement?
+                           defaultStatement? configStatement? mandatoryStatement? minElementsStatement?
+                           maxElementsStatement? RIGHT_CURLY_BRACE));
+
+    /**
+     *   compiler-annotation-stmt = prefix:compiler-annotation-keyword string
+     *                          "{"
+     *                              [app-data-structure-stmt stmtsep]
+     *                              [app-extended-stmt stmtsep]
+     *                          "}"
+     */
+    compilerAnnotationStatement : COMPILER_ANNOTATION string LEFT_CURLY_BRACE
+                                       compilerAnnotationBodyStatement RIGHT_CURLY_BRACE;
+
+    compilerAnnotationBodyStatement : appDataStructureStatement? appExtendedStatement? ;
+
+    /**
+     *   app-data-structure-stmt = prefix:app-data-structure-keyword string
+     *                         (";" /
+     *                          "{"
+     *                              [data-structure-key-stmt stmtsep]
+     *                          "}")
+     */
+    appDataStructureStatement : APP_DATA_STRUCTURE appDataStructure (STMTEND | (LEFT_CURLY_BRACE
+                  dataStructureKeyStatement? RIGHT_CURLY_BRACE));
+
+    /**
+     *   data-structure-key-stmt = prefix:key-keyword string ";"
+     */
+    dataStructureKeyStatement : DATA_STRUCTURE_KEY string STMTEND;
+
+    /**
+     *   app-extended-stmt = prefix:app-extended-name-keyword string ";"
+     */
+    appExtendedStatement : APP_EXTENDED extendedName STMTEND;
+
+    string : STRING (PLUS STRING)*
+           | IDENTIFIER
+           | INTEGER
+           | yangConstruct;
+
+    identifier : STRING (PLUS STRING)*
+               | IDENTIFIER
+               | yangConstruct;
+
+    dateArgumentString : DATE_ARG
+                       | STRING (PLUS STRING)*;
+
+    version : string;
+
+    range : string;
+
+    length : string;
+
+    path : string;
+
+    position : string;
+
+    status : string;
+
+    config : string;
+
+    mandatory : string;
+
+    orderedBy : string;
+
+    minValue : string;
+
+    maxValue : string;
+
+    key : string;
+
+    unique : string;
+
+    refine : string;
+
+    requireInstance : string;
+
+    augment : string;
+
+    deviation : string;
+
+    value : string;
+
+    fraction : string;
+
+    appDataStructure : string;
+
+    extendedName : string;
+
+    yangConstruct : ANYXML_KEYWORD | ARGUMENT_KEYWORD | AUGMENT_KEYWORD | BASE_KEYWORD | BELONGS_TO_KEYWORD
+                  | BIT_KEYWORD | CASE_KEYWORD | CHOICE_KEYWORD | CONFIG_KEYWORD | CONTACT_KEYWORD | CONTAINER_KEYWORD
+                  | DEFAULT_KEYWORD | DESCRIPTION_KEYWORD | ENUM_KEYWORD | ERROR_APP_TAG_KEYWORD | ERROR_MESSAGE_KEYWORD
+                  | EXTENSION_KEYWORD | DEVIATION_KEYWORD | DEVIATE_KEYWORD | FEATURE_KEYWORD
+                  | FRACTION_DIGITS_KEYWORD | GROUPING_KEYWORD | IDENTITY_KEYWORD | IF_FEATURE_KEYWORD
+                  | IMPORT_KEYWORD | INCLUDE_KEYWORD | INPUT_KEYWORD | KEY_KEYWORD | LEAF_KEYWORD | LEAF_LIST_KEYWORD
+                  | LENGTH_KEYWORD | LIST_KEYWORD | MANDATORY_KEYWORD | MAX_ELEMENTS_KEYWORD | MIN_ELEMENTS_KEYWORD
+                  | MODULE_KEYWORD | MUST_KEYWORD | NAMESPACE_KEYWORD | NOTIFICATION_KEYWORD | ORDERED_BY_KEYWORD
+                  | ORGANIZATION_KEYWORD | OUTPUT_KEYWORD | PATH_KEYWORD | PATTERN_KEYWORD | POSITION_KEYWORD
+                  | PREFIX_KEYWORD | PRESENCE_KEYWORD | RANGE_KEYWORD | REFERENCE_KEYWORD | REFINE_KEYWORD
+                  | REQUIRE_INSTANCE_KEYWORD | REVISION_KEYWORD | REVISION_DATE_KEYWORD | RPC_KEYWORD
+                  | STATUS_KEYWORD | SUBMODULE_KEYWORD | TYPE_KEYWORD | TYPEDEF_KEYWORD | UNIQUE_KEYWORD
+                  | UNITS_KEYWORD | USES_KEYWORD | VALUE_KEYWORD | WHEN_KEYWORD | YANG_VERSION_KEYWORD
+                  | YIN_ELEMENT_KEYWORD | ADD_KEYWORD | CURRENT_KEYWORD | DELETE_KEYWORD | DEPRECATED_KEYWORD
+                  | FALSE_KEYWORD | MAX_KEYWORD | MIN_KEYWORD | NOT_SUPPORTED_KEYWORD | OBSOLETE_KEYWORD
+                  | REPLACE_KEYWORD | SYSTEM_KEYWORD | TRUE_KEYWORD | UNBOUNDED_KEYWORD | USER_KEYWORD
+                  | COMPILER_ANNOTATION_KEYWORD | APP_DATA_STRUCTURE_KEYWORD | DATA_STRUCTURE_KEYWORD
+                  | APP_EXTENDED_KEYWORD;
diff --git a/parser/src/main/resources/YangLexer.g4 b/parser/src/main/resources/YangLexer.g4
new file mode 100644
index 0000000..51a9231
--- /dev/null
+++ b/parser/src/main/resources/YangLexer.g4
@@ -0,0 +1,146 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * This is a YANG grammar for lexer based on which ANTLR will generate YANG lexer.
+ */
+
+lexer grammar YangLexer;
+
+    // Statements keywords
+    ANYXML_KEYWORD      : 'anyxml';
+    ARGUMENT_KEYWORD    : 'argument';
+    AUGMENT_KEYWORD     : 'augment';
+    BASE_KEYWORD        : 'base';
+    BELONGS_TO_KEYWORD  : 'belongs-to';
+    BIT_KEYWORD         : 'bit';
+    CASE_KEYWORD        : 'case';
+    CHOICE_KEYWORD      : 'choice';
+    CONFIG_KEYWORD      : 'config';
+    CONTACT_KEYWORD     : 'contact';
+    CONTAINER_KEYWORD   : 'container';
+    DEFAULT_KEYWORD     : 'default';
+    DESCRIPTION_KEYWORD : 'description';
+    ENUM_KEYWORD        : 'enum';
+    ERROR_APP_TAG_KEYWORD : 'error-app-tag';
+    ERROR_MESSAGE_KEYWORD : 'error-message';
+    EXTENSION_KEYWORD   : 'extension';
+    DEVIATION_KEYWORD   : 'deviation';
+    DEVIATE_KEYWORD     : 'deviate';
+    FEATURE_KEYWORD     : 'feature';
+    FRACTION_DIGITS_KEYWORD : 'fraction-digits';
+    GROUPING_KEYWORD    : 'grouping';
+    IDENTITY_KEYWORD    : 'identity';
+    IF_FEATURE_KEYWORD  : 'if-feature';
+    IMPORT_KEYWORD      : 'import';
+    INCLUDE_KEYWORD     : 'include';
+    INPUT_KEYWORD       : 'input';
+    KEY_KEYWORD         : 'key';
+    LEAF_KEYWORD        : 'leaf';
+    LEAF_LIST_KEYWORD   : 'leaf-list';
+    LENGTH_KEYWORD      : 'length';
+    LIST_KEYWORD        : 'list';
+    MANDATORY_KEYWORD   : 'mandatory';
+    MAX_ELEMENTS_KEYWORD : 'max-elements';
+    MIN_ELEMENTS_KEYWORD : 'min-elements';
+    MODULE_KEYWORD      : 'module';
+    MUST_KEYWORD        : 'must';
+    NAMESPACE_KEYWORD   : 'namespace';
+    NOTIFICATION_KEYWORD: 'notification';
+    ORDERED_BY_KEYWORD  : 'ordered-by';
+    ORGANIZATION_KEYWORD: 'organization';
+    OUTPUT_KEYWORD      : 'output';
+    PATH_KEYWORD        : 'path';
+    PATTERN_KEYWORD     : 'pattern';
+    POSITION_KEYWORD    : 'position';
+    PREFIX_KEYWORD      : 'prefix';
+    PRESENCE_KEYWORD    : 'presence';
+    RANGE_KEYWORD       : 'range';
+    REFERENCE_KEYWORD   : 'reference';
+    REFINE_KEYWORD      : 'refine';
+    REQUIRE_INSTANCE_KEYWORD : 'require-instance';
+    REVISION_KEYWORD    : 'revision';
+    REVISION_DATE_KEYWORD : 'revision-date';
+    RPC_KEYWORD         : 'rpc';
+    STATUS_KEYWORD      : 'status';
+    SUBMODULE_KEYWORD   : 'submodule';
+    TYPE_KEYWORD        : 'type';
+    TYPEDEF_KEYWORD     : 'typedef';
+    UNIQUE_KEYWORD      : 'unique';
+    UNITS_KEYWORD       : 'units';
+    USES_KEYWORD        : 'uses';
+    VALUE_KEYWORD       : 'value';
+    WHEN_KEYWORD        : 'when';
+    YANG_VERSION_KEYWORD: 'yang-version';
+    YIN_ELEMENT_KEYWORD : 'yin-element';
+    ADD_KEYWORD         : 'add';
+    CURRENT_KEYWORD     : 'current';
+    DELETE_KEYWORD      : 'delete';
+    DEPRECATED_KEYWORD  : 'deprecated';
+    FALSE_KEYWORD       : 'false';
+    MAX_KEYWORD         : 'max';
+    MIN_KEYWORD         : 'min';
+    NOT_SUPPORTED_KEYWORD : 'not-supported';
+    OBSOLETE_KEYWORD    : 'obsolete';
+    REPLACE_KEYWORD     : 'replace';
+    SYSTEM_KEYWORD      : 'system';
+    TRUE_KEYWORD        : 'true';
+    UNBOUNDED_KEYWORD   : 'unbounded';
+    USER_KEYWORD        : 'user';
+    COMPILER_ANNOTATION_KEYWORD : 'compiler-annotation';
+    COMPILER_ANNOTATION : IDENTIFIER COLON COMPILER_ANNOTATION_KEYWORD;
+    APP_DATA_STRUCTURE_KEYWORD : 'app-data-structure';
+    APP_DATA_STRUCTURE : IDENTIFIER COLON APP_DATA_STRUCTURE_KEYWORD;
+    DATA_STRUCTURE_KEYWORD : 'data-structure';
+    DATA_STRUCTURE : IDENTIFIER COLON DATA_STRUCTURE_KEYWORD;
+    DATA_STRUCTURE_KEY : IDENTIFIER COLON KEY_KEYWORD;
+    APP_EXTENDED_KEYWORD : 'app-extended-name';
+    APP_EXTENDED : IDENTIFIER COLON APP_EXTENDED_KEYWORD;
+
+    // Lexer tokens to be skipped
+    COMMENT
+        :   '/*' .*? '*/'    -> channel(HIDDEN)
+        ;
+    WS  :   [ \r\t\u000C\n]+ -> channel(HIDDEN)
+        ;
+    LINE_COMMENT
+        : '//' ~[\r\n]* '\r'? '\n' -> channel(HIDDEN)
+        ;
+
+    // Additional rules
+    INTEGER             : DIGIT+;
+    DATE_ARG            : DIGIT DIGIT DIGIT DIGIT '-' DIGIT DIGIT '-' DIGIT DIGIT;
+    LEFT_CURLY_BRACE    : '{';
+    RIGHT_CURLY_BRACE   : '}';
+    IDENTIFIER          : (ALPHA | '_')
+                          (ALPHA | DIGIT | '_' | '-' | '.')*;
+    STMTEND             : ';';
+    DQUOTE              : '"';
+    COLON               : ':';
+    PLUS : '+';
+    MINUS: '-';
+
+    STRING : ((~( '\r' | '\n' | '\t' | ' ' | ';' | '{' | '"' | '+' | '\'')~( '\r' | '\n' | '\t' | ' ' | ';' | '{' | '+')* ) | SUB_STRING );
+
+    //Fragment rules
+    fragment SUB_STRING : ('"' (ESC | ~["])*'"') | ('\'' (ESC | ~['])*'\'') ;
+    fragment ESC :  '\\' (["\\/bfnrt] | UNICODE) ;
+    fragment UNICODE : 'u' HEX HEX HEX HEX ;
+    fragment HEX : [0-9a-fA-F] ;
+    fragment ALPHA      : [A-Za-z];
+    fragment DIGIT      : [0-9];
+    fragment URN        : [u][r][n];
+    fragment HTTP       : [h][t][t][p];
\ No newline at end of file