diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangCase.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangCase.java
index bb3c3cc..6677a8c 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangCase.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangCase.java
@@ -354,7 +354,7 @@
     @Override
     public void detectCollidingChild(String identifierName, YangConstructType dataType)
             throws DataModelException {
-        if (!(getParent() instanceof YangChoice)) {
+        if (!(getParent() instanceof YangChoice || getParent() instanceof YangAugment)) {
             throw new DataModelException("Internal Data Model Tree Error: Invalid/Missing holder in case " +
                     getName());
         }
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangExtension.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangExtension.java
new file mode 100644
index 0000000..b22f6d1
--- /dev/null
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangExtension.java
@@ -0,0 +1,219 @@
+/*
+ * 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.datamodel;
+
+import java.io.Serializable;
+import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.datamodel.utils.Parsable;
+import org.onosproject.yangutils.datamodel.utils.YangConstructType;
+
+/*-
+ * Reference RFC 6020.
+ *
+ * The "extension" statement allows the definition of new statements
+ * within the YANG language.  This new statement definition can be
+ * imported and used by other modules.
+ *
+ * The statement's argument is an identifier that is the new keyword for
+ * the extension and must be followed by a block of sub-statements that
+ * holds detailed extension information.  The purpose of the "extension"
+ * statement is to define a keyword, so that it can be imported and used
+ * by other modules.
+ *
+ * The extension can be used like a normal YANG statement, with the
+ * statement name followed by an argument if one is defined by the
+ * extension, and an optional block of sub-statements.  The statement's
+ * name is created by combining the prefix of the module in which the
+ * extension was defined, a colon (":"), and the extension's keyword,
+ * with no interleaving whitespace.  The sub-statements of an extension
+ * are defined by the extension, using some mechanism outside the scope
+ * of this specification.  Syntactically, the sub-statements MUST be YANG
+ * statements, or also defined using "extension" statements.
+ *
+ * The extension's Sub-statements
+ *
+ *                +--------------+---------+-------------+------------------+
+ *                | substatement | section | cardinality |data model mapping|
+ *                +--------------+---------+-------------+------------------+
+ *                | description  | 7.19.3  | 0..1        | -string          |
+ *                | reference    | 7.19.4  | 0..1        | -string          |
+ *                | status       | 7.19.2  | 0..1        | -YangStatus      |
+ *                | argument     | 7.17.2  | 0..1        | -string          |
+ *                +--------------+---------+-------------+------------------+
+ */
+
+/**
+ * Represents data model node to maintain information defined in YANG extension.
+ */
+public class YangExtension
+        implements YangCommonInfo, Serializable, Parsable {
+
+    private static final long serialVersionUID = 806201605L;
+
+    /**
+     * Name of the extension.
+     */
+    private String name;
+
+    /**
+     * Name of the argument.
+     */
+    private String argumentName;
+
+    /**
+     * Description of extension.
+     */
+    private String description;
+
+    /**
+     * Reference of the extension.
+     */
+    private String reference;
+
+    /**
+     * Status of the extension.
+     */
+    private YangStatusType status = YangStatusType.CURRENT;
+
+    /**
+     * Returns the YANG name of extension.
+     *
+     * @return the name of extension as defined in YANG file
+     */
+    public String getName() {
+        return name;
+    }
+
+    /**
+     * Sets the YANG name of extension.
+     *
+     * @param name the name of extension as defined in YANG file
+     */
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    /**
+     * Returns the YANG argument name of extension.
+     *
+     * @return the name of argument as defined in YANG file
+     */
+    public String getArgumentName() {
+        return argumentName;
+    }
+
+    /**
+     * Sets the YANG argument name of extension.
+     *
+     * @param argumentName the name of argument as defined in YANG file
+     */
+    public void setArgumentName(String argumentName) {
+        this.argumentName = argumentName;
+    }
+
+    /**
+     * Returns the description.
+     *
+     * @return the description
+     */
+    @Override
+    public String getDescription() {
+        return description;
+    }
+
+    /**
+     * Sets the description.
+     *
+     * @param description set the description
+     */
+    @Override
+    public void setDescription(String description) {
+        this.description = description;
+    }
+
+    /**
+     * Returns the textual reference.
+     *
+     * @return the reference
+     */
+    @Override
+    public String getReference() {
+        return reference;
+    }
+
+    /**
+     * Sets the textual reference.
+     *
+     * @param reference the reference to set
+     */
+    @Override
+    public void setReference(String reference) {
+        this.reference = reference;
+    }
+
+    /**
+     * Returns the status.
+     *
+     * @return the status
+     */
+    @Override
+    public YangStatusType getStatus() {
+        return status;
+    }
+
+    /**
+     * Sets the status.
+     *
+     * @param status the status to set
+     */
+    @Override
+    public void setStatus(YangStatusType status) {
+        this.status = status;
+    }
+
+    /**
+     * Returns the type of the data.
+     *
+     * @return returns EXTENSION_DATA
+     */
+    @Override
+    public YangConstructType getYangConstructType() {
+        return YangConstructType.EXTENSION_DATA;
+    }
+
+    /**
+     * Validates the data on entering the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules
+     */
+    @Override
+    public void validateDataOnEntry()
+            throws DataModelException {
+        // TODO auto-generated method stub, to be implemented by parser
+    }
+
+    /**
+     * Validates the data on exiting the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules
+     */
+    @Override
+    public void validateDataOnExit()
+            throws DataModelException {
+        // TODO : to be implemented
+    }
+}
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangModule.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangModule.java
index 81bbd41..f9b1e87 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangModule.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangModule.java
@@ -231,6 +231,11 @@
     private List<YangResolutionInfo> augmentResolutionList;
 
     /**
+     * extension list.
+     */
+    private List<YangExtension> extensionList;
+
+    /**
      * Creates a YANG node of module type.
      */
     public YangModule() {
@@ -247,6 +252,7 @@
         includeList = new LinkedList<YangInclude>();
         listOfLeaf = new LinkedList<YangLeaf>();
         listOfLeafList = new LinkedList<YangLeafList>();
+        extensionList = new LinkedList<YangExtension>();
     }
 
     /**
@@ -557,6 +563,33 @@
     }
 
     /**
+     * Adds extension in extension list.
+     *
+     * @param extension the extension to be added
+     */
+    public void addExtension(YangExtension extension) {
+        getExtensionList().add(extension);
+    }
+
+    /**
+     * Returns the extension list.
+     *
+     * @return the extension list
+     */
+    public List<YangExtension> getExtensionList() {
+        return extensionList;
+    }
+
+    /**
+     * Sets the extension list.
+     *
+     * @param extensionList the list of extension
+     */
+    public void setExtensionList(List<YangExtension> extensionList) {
+        this.extensionList = extensionList;
+    }
+
+    /**
      * Returns the type of the parsed data.
      *
      * @return returns MODULE_DATA
@@ -639,7 +672,7 @@
             leafrefResolutionList.add(resolutionInfo);
         } else if (type == ResolvableType.YANG_BASE) {
             baseResolutionList.add(resolutionInfo);
-        } else if (type ==  ResolvableType.YANG_AUGMENT) {
+        } else if (type == ResolvableType.YANG_AUGMENT) {
             augmentResolutionList.add(resolutionInfo);
         } else if (type == ResolvableType.YANG_IDENTITYREF) {
             identityrefResolutionList.add(resolutionInfo);
@@ -659,7 +692,7 @@
             leafrefResolutionList = resolutionList;
         } else if (type == ResolvableType.YANG_BASE) {
             baseResolutionList = resolutionList;
-        } else if (type ==  ResolvableType.YANG_AUGMENT) {
+        } else if (type == ResolvableType.YANG_AUGMENT) {
             augmentResolutionList = resolutionList;
         } else if (type == ResolvableType.YANG_IDENTITYREF) {
             identityrefResolutionList = resolutionList;
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangSubModule.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangSubModule.java
index 438dc1f..f8bec7c 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangSubModule.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangSubModule.java
@@ -224,6 +224,11 @@
     private List<YangResolutionInfo> identityrefResolutionList;
 
     /**
+     * extension list.
+     */
+    private List<YangExtension> extensionList;
+
+    /**
      * Augment resolution list.
      */
     private List<YangResolutionInfo> augmentResolutionList;
@@ -244,6 +249,7 @@
         includeList = new LinkedList<YangInclude>();
         listOfLeaf = new LinkedList<YangLeaf>();
         listOfLeafList = new LinkedList<YangLeafList>();
+        extensionList = new LinkedList<YangExtension>();
     }
 
     /**
@@ -601,7 +607,7 @@
             leafrefResolutionList.add(resolutionInfo);
         } else if (type == ResolvableType.YANG_BASE) {
             baseResolutionList.add(resolutionInfo);
-        } else if (type ==  ResolvableType.YANG_AUGMENT) {
+        } else if (type == ResolvableType.YANG_AUGMENT) {
             augmentResolutionList.add(resolutionInfo);
         } else if (type == ResolvableType.YANG_IDENTITYREF) {
             identityrefResolutionList.add(resolutionInfo);
@@ -621,7 +627,7 @@
             leafrefResolutionList = resolutionList;
         } else if (type == ResolvableType.YANG_BASE) {
             baseResolutionList = resolutionList;
-        } else if (type ==  ResolvableType.YANG_AUGMENT) {
+        } else if (type == ResolvableType.YANG_AUGMENT) {
             augmentResolutionList = resolutionList;
         } else if (type == ResolvableType.YANG_IDENTITYREF) {
             identityrefResolutionList = resolutionList;
@@ -684,4 +690,31 @@
     public void setListOfFeature(List<YangFeature> listOfFeature) {
         this.listOfFeature = listOfFeature;
     }
+
+    /**
+     * Adds extension in extension list.
+     *
+     * @param extension the extension to be added
+     */
+    public void addExtension(YangExtension extension) {
+        getExtensionList().add(extension);
+    }
+
+    /**
+     * Returns the extension list.
+     *
+     * @return the extension list
+     */
+    public List<YangExtension> getExtensionList() {
+        return extensionList;
+    }
+
+    /**
+     * Sets the extension list.
+     *
+     * @param extensionList the list of extension
+     */
+    public void setExtensionList(List<YangExtension> extensionList) {
+        this.extensionList = extensionList;
+    }
 }
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/utils/YangConstructType.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/utils/YangConstructType.java
index efe5620..e0dd8e3 100644
--- a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/utils/YangConstructType.java
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/utils/YangConstructType.java
@@ -382,7 +382,12 @@
     /**
      * Identifies the YANG anyxml element parsed data.
      */
-    ANYXML_DATA;
+    ANYXML_DATA,
+
+    /**
+     * Identifies the YANG argument element parsed data.
+     */
+    ARGUMENT_DATA;
 
     /**
      * Returns the YANG construct keyword corresponding to enum values.
@@ -539,6 +544,8 @@
                 return "deviation";
             case ANYXML_DATA:
                 return "anyxml";
+            case ARGUMENT_DATA:
+                return "argument";
             default:
                 return "yang";
         }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/linker/impl/YangResolutionInfoImpl.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/linker/impl/YangResolutionInfoImpl.java
index e7abe15..5c680cd 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/linker/impl/YangResolutionInfoImpl.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/linker/impl/YangResolutionInfoImpl.java
@@ -16,8 +16,14 @@
 
 package org.onosproject.yangutils.linker.impl;
 
+import java.io.Serializable;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
 import org.onosproject.yangutils.datamodel.Resolvable;
 import org.onosproject.yangutils.datamodel.ResolvableType;
+import org.onosproject.yangutils.datamodel.TraversalType;
 import org.onosproject.yangutils.datamodel.YangAtomicPath;
 import org.onosproject.yangutils.datamodel.YangAugment;
 import org.onosproject.yangutils.datamodel.YangAugmentableNode;
@@ -58,12 +64,10 @@
 import org.onosproject.yangutils.linker.YangLinkingPhase;
 import org.onosproject.yangutils.linker.exceptions.LinkerException;
 
-import java.io.Serializable;
-import java.util.Iterator;
-import java.util.LinkedList;
-import java.util.List;
-import java.util.Stack;
-
+import static org.onosproject.yangutils.datamodel.TraversalType.CHILD;
+import static org.onosproject.yangutils.datamodel.TraversalType.PARENT;
+import static org.onosproject.yangutils.datamodel.TraversalType.ROOT;
+import static org.onosproject.yangutils.datamodel.TraversalType.SIBILING;
 import static org.onosproject.yangutils.datamodel.utils.DataModelUtils.addResolutionInfo;
 import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.INTER_FILE_LINKED;
 import static org.onosproject.yangutils.datamodel.utils.ResolvableStatus.INTRA_FILE_RESOLVED;
@@ -1007,16 +1011,33 @@
         /**
          * Search the grouping node's children for presence of uses node.
          */
+        TraversalType curTraversal = ROOT;
         YangNode curNode = node.getChild();
         while (curNode != null) {
+            if (curNode.getName().equals(node.getName())) {
+                // if we have traversed all the child nodes, then exit from loop
+                return;
+            }
+
+            // if child nodes has uses, then add it to resolution stack
             if (curNode instanceof YangUses) {
                 YangEntityToResolveInfoImpl<YangUses> unResolvedEntityInfo = new YangEntityToResolveInfoImpl<>();
                 unResolvedEntityInfo.setEntityToResolve((YangUses) curNode);
                 unResolvedEntityInfo.setHolderOfEntityToResolve(node);
                 addInPartialResolvedStack((YangEntityToResolveInfoImpl<T>) unResolvedEntityInfo);
-
             }
-            curNode = curNode.getNextSibling();
+
+            // Traversing all the child nodes of grouping
+            if (curTraversal != PARENT && curNode.getChild() != null) {
+                curTraversal = CHILD;
+                curNode = curNode.getChild();
+            } else if (curNode.getNextSibling() != null) {
+                curTraversal = SIBILING;
+                curNode = curNode.getNextSibling();
+            } else {
+                curTraversal = PARENT;
+                curNode = curNode.getParent();
+            }
         }
     }
 
@@ -1421,7 +1442,7 @@
      * @param resolutionInfo information about the YANG construct which has to be resolved
      * @throws DataModelException a violation of data model rules
      */
-    public void setAbsolutePathFromRelativePathInLeafref(T resolutionInfo) throws  DataModelException {
+    public void setAbsolutePathFromRelativePathInLeafref(T resolutionInfo) throws DataModelException {
         if (resolutionInfo instanceof YangLeafRef) {
 
             YangNode parentOfLeafref = ((YangLeafRef) resolutionInfo).getParentNodeOfLeafref();
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
index 7b0d17f..2b9021b 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
@@ -24,6 +24,7 @@
 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.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;
@@ -42,6 +43,7 @@
 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;
@@ -436,12 +438,12 @@
 
     @Override
     public void enterExtensionStatement(GeneratedYangParser.ExtensionStatementContext ctx) {
-        handleUnsupportedYangConstruct(YangConstructType.EXTENSION_DATA, ctx, UNSUPPORTED_YANG_CONSTRUCT);
+        ExtensionListener.processExtensionEntry(this, ctx);
     }
 
     @Override
     public void exitExtensionStatement(GeneratedYangParser.ExtensionStatementContext ctx) {
-        // do nothing
+        ExtensionListener.processExtensionExit(this, ctx);
     }
 
     @Override
@@ -456,7 +458,7 @@
 
     @Override
     public void enterArgumentStatement(GeneratedYangParser.ArgumentStatementContext ctx) {
-        // do nothing.
+        ArgumentListener.processArgumentEntry(this, ctx);
     }
 
     @Override
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java
new file mode 100644
index 0000000..2d06fa4
--- /dev/null
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ArgumentListener.java
@@ -0,0 +1,84 @@
+/*
+ * 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.setArgumentName(identifier);
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, ARGUMENT_DATA,
+                    ctx.identifier().getText(), ENTRY));
+        }
+    }
+}
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java
index f049be0..6c6a38d 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/AugmentListener.java
@@ -52,8 +52,8 @@
 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.parser.impl.parserutils.ListenerValidation.validateMutuallyExclusiveChilds;
 import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangAugmentNode;
 
 /*
@@ -176,8 +176,8 @@
         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());
-        validateMutuallyExclusiveChilds(ctx.dataDefStatement(), DATA_DEF_DATA, ctx.caseStatement(),
-                CASE_DATA, AUGMENT_DATA, ctx.augment().getText());
+        validateCardinalityEitherOne(ctx.dataDefStatement(), DATA_DEF_DATA, ctx.caseStatement(),
+                CASE_DATA, AUGMENT_DATA, ctx.augment().getText(), ctx);
     }
 
     /**
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java
index 5aa1dcd..3078c08 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/CaseListener.java
@@ -16,6 +16,7 @@
 
 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;
@@ -104,7 +105,7 @@
         int charPositionInLine = ctx.getStart().getCharPositionInLine();
         detectCollidingChildUtil(listener, line, charPositionInLine, identifier, CASE_DATA);
 
-        if (curData instanceof YangChoice) {
+        if (curData instanceof YangChoice || curData instanceof YangAugment) {
             YangCase caseNode = getYangCaseNode(JAVA_GENERATION);
             caseNode.setName(identifier);
             YangNode curNode = (YangNode) curData;
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java
index 61c2df1..b6a583a 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ChoiceListener.java
@@ -35,14 +35,12 @@
 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.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.SHORT_CASE_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;
@@ -57,7 +55,6 @@
 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.parser.impl.parserutils.ListenerValidation.validateMutuallyExclusiveChilds;
 import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangChoiceNode;
 
 /*
@@ -181,7 +178,5 @@
         validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, CHOICE_DATA,
                 ctx.identifier().getText());
         validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, CHOICE_DATA, ctx.identifier().getText());
-        validateMutuallyExclusiveChilds(ctx.shortCaseStatement(), SHORT_CASE_DATA, ctx.caseStatement(), CASE_DATA,
-                CHOICE_DATA, ctx.identifier().getText());
     }
 }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java
index 9ed3e76..5a89cc3 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ContainerListener.java
@@ -171,8 +171,11 @@
             try {
                 yangContainer.validateDataOnExit();
             } catch (DataModelException e) {
-                throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA,
-                        CONTAINER_DATA, ctx.identifier().getText(), EXIT, e.getMessage()));
+                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 {
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java
new file mode 100644
index 0000000..2169640
--- /dev/null
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListener.java
@@ -0,0 +1,121 @@
+/*
+ * 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.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/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java
index 04d7f50..fd2ac3d 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/GroupingListener.java
@@ -37,7 +37,6 @@
 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.datamodel.utils.YangConstructType.TYPEDEF_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;
@@ -50,7 +49,6 @@
 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.parser.impl.parserutils.ListenerValidation.validateMutuallyExclusiveChilds;
 import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangGroupingNode;
 
 /*
@@ -172,7 +170,5 @@
         validateCardinalityMaxOne(ctx.descriptionStatement(), DESCRIPTION_DATA, GROUPING_DATA,
                 ctx.identifier().getText());
         validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, GROUPING_DATA, ctx.identifier().getText());
-        validateMutuallyExclusiveChilds(ctx.typedefStatement(), TYPEDEF_DATA, ctx.groupingStatement(), GROUPING_DATA,
-                GROUPING_DATA, ctx.identifier().getText());
     }
 }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java
index 6088ab4..4ed7493 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/NotificationListener.java
@@ -28,11 +28,9 @@
 
 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.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.datamodel.utils.YangConstructType.TYPEDEF_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;
@@ -45,7 +43,6 @@
 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.parser.impl.parserutils.ListenerValidation.validateMutuallyExclusiveChilds;
 import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangNotificationNode;
 
 /*
@@ -159,7 +156,5 @@
                 ctx.identifier().getText());
         validateCardinalityMaxOne(ctx.referenceStatement(), REFERENCE_DATA, NOTIFICATION_DATA,
                 ctx.identifier().getText());
-        validateMutuallyExclusiveChilds(ctx.typedefStatement(), TYPEDEF_DATA, ctx.groupingStatement(), GROUPING_DATA,
-                NOTIFICATION_DATA, ctx.identifier().getText());
     }
 }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java
index afb78a3..1c56fe5 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/listeners/RpcListener.java
@@ -16,9 +16,9 @@
 
 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.YangModule;
 import org.onosproject.yangutils.datamodel.YangSubModule;
 import org.onosproject.yangutils.datamodel.exceptions.DataModelException;
 import org.onosproject.yangutils.datamodel.utils.Parsable;
@@ -28,23 +28,23 @@
 
 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.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.datamodel.utils.YangConstructType.TYPEDEF_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.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
-import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.*;
+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.parser.impl.parserutils.ListenerValidation.validateMutuallyExclusiveChilds;
 import static org.onosproject.yangutils.translator.tojava.YangDataModelFactory.getYangRpcNode;
 
 /*
@@ -157,8 +157,6 @@
         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());
-        validateMutuallyExclusiveChilds(ctx.typedefStatement(), TYPEDEF_DATA, ctx.groupingStatement(), GROUPING_DATA,
-                RPC_DATA, ctx.identifier().getText());
     }
 
 }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java
index f5e98d0..188e24e 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerValidation.java
@@ -208,29 +208,30 @@
     /**
      * Checks if a either of one construct occurrence.
      *
-     * @param child1Context first optional child's context
+     * @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 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 parentName          parent name
+     * @param parentContext       parents's context
      * @throws ParserException exception if cardinality check fails
      */
-    public static void validateMutuallyExclusiveChilds(List<?> child1Context, YangConstructType yangChild1Construct,
-            List<?> child2Context, YangConstructType yangChild2Construct,
-            YangConstructType yangParentConstruct, String parentName)
+    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: \""
-                    + getYangConstructType(yangChild1Construct) + "\" & \"" + getYangConstructType(yangChild2Construct)
-                    + "\" should be mutually exclusive in \"" + getYangConstructType(yangParentConstruct) + " "
+        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(((ParserRuleContext) child2Context).getStart().getLine());
-            parserException.setCharPosition(((ParserRuleContext) child2Context).getStart().getCharPositionInLine());
+            parserException.setLine(parentContext.getStart().getLine());
+            parserException.setCharPosition(parentContext.getStart().getCharPositionInLine());
             throw parserException;
         }
     }
diff --git a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/translator/tojava/TempJavaFragmentFiles.java b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/translator/tojava/TempJavaFragmentFiles.java
index 19c2d54..982f7c3 100644
--- a/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/translator/tojava/TempJavaFragmentFiles.java
+++ b/utils/yangutils/plugin/src/main/java/org/onosproject/yangutils/translator/tojava/TempJavaFragmentFiles.java
@@ -103,6 +103,7 @@
 import static org.onosproject.yangutils.utils.UtilConstants.SEMI_COLAN;
 import static org.onosproject.yangutils.utils.UtilConstants.SERVICE;
 import static org.onosproject.yangutils.utils.UtilConstants.SLASH;
+import static org.onosproject.yangutils.utils.UtilConstants.YANG_AUGMENTED_INFO;
 import static org.onosproject.yangutils.utils.io.impl.FileSystemUtil.closeFile;
 import static org.onosproject.yangutils.utils.io.impl.FileSystemUtil.readAppendFile;
 import static org.onosproject.yangutils.utils.io.impl.JavaDocGen.JavaDocType.GETTER_METHOD;
@@ -1688,6 +1689,12 @@
      */
     private void removeAugmentedInfoImport(List<String> imports) {
         imports.remove(getJavaImportData().getYangAugmentedInfoImport());
+        for (JavaQualifiedTypeInfo type : getJavaImportData().getImportSet()) {
+            if (type.getClassInfo().equals(YANG_AUGMENTED_INFO)) {
+                getJavaImportData().getImportSet().remove(type);
+                getJavaExtendsListHolder().getExtendsList().remove(type);
+            }
+        }
     }
 
     /**
diff --git a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/CaseListenerTest.java b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/CaseListenerTest.java
index 675a9e9..9ebf0df 100644
--- a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/CaseListenerTest.java
+++ b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/CaseListenerTest.java
@@ -16,9 +16,10 @@
 
 package org.onosproject.yangutils.parser.impl.listeners;
 
-import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.core.Is.is;
+import java.io.IOException;
+import java.util.ListIterator;
 import org.junit.Test;
+import org.onosproject.yangutils.datamodel.YangAugment;
 import org.onosproject.yangutils.datamodel.YangCase;
 import org.onosproject.yangutils.datamodel.YangChoice;
 import org.onosproject.yangutils.datamodel.YangContainer;
@@ -29,8 +30,8 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.YangUtilsParserManager;
 
-import java.io.IOException;
-import java.util.ListIterator;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
 
 /**
  * Test cases for case listener.
@@ -202,4 +203,36 @@
         YangLeaf leafInfo2 = leafIterator2.next();
         assertThat(leafInfo2.getName(), is("beer"));
     }
+
+    /**
+     * Checks case substatement of augment.
+     */
+    @Test
+    public void processCaseSubStatementOfAugment() throws IOException, ParserException {
+
+        YangNode node = manager.getDataModel("src/test/resources/CaseSubStatementOfAugment.yang");
+
+        // Check whether the data model tree returned is of type module.
+        assertThat((node instanceof YangModule), is(true));
+
+        // Check whether the node type is set properly to module.
+        assertThat(node.getNodeType(), is(YangNodeType.MODULE_NODE));
+
+        // Check whether the module name is set correctly.
+        YangModule yangNode = (YangModule) node;
+        assertThat(yangNode.getName(), is("event"));
+
+        YangAugment augment = ((YangAugment) yangNode.getChild());
+        assertThat(augment.getName(), is("/snmp:snmp/snmp:engine/snmp:listen/snmp:transport"));
+
+        YangCase yangCase = ((YangCase) augment.getChild());
+        assertThat(yangCase.getName(), is("tls"));
+
+        YangCase yangCase1 = ((YangCase) yangCase.getNextSibling());
+        assertThat(yangCase1.getName(), is("dtls"));
+
+        YangContainer container = ((YangContainer) yangCase.getChild());
+        assertThat(container.getName(), is("tls"));
+        assertThat(container.getListOfLeaf().iterator().next().getName(), is("ip"));
+    }
 }
diff --git a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListenerTest.java b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListenerTest.java
new file mode 100644
index 0000000..d5c3c83
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ExtensionListenerTest.java
@@ -0,0 +1,60 @@
+/*
+ * 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.io.IOException;
+import org.junit.Test;
+import org.onosproject.yangutils.datamodel.YangExtension;
+import org.onosproject.yangutils.datamodel.YangModule;
+import org.onosproject.yangutils.datamodel.YangNode;
+import org.onosproject.yangutils.datamodel.YangNodeType;
+import org.onosproject.yangutils.parser.exceptions.ParserException;
+import org.onosproject.yangutils.parser.impl.YangUtilsParserManager;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.core.Is.is;
+
+/**
+ * Test cases for testing extension listener.
+ */
+public class ExtensionListenerTest {
+
+    private final YangUtilsParserManager manager = new YangUtilsParserManager();
+
+    /**
+     * Checks extension statement as sub-statement of module.
+     */
+    @Test
+    public void processValidExtensionStatement() throws IOException, ParserException {
+
+        YangNode node = manager.getDataModel("src/test/resources/ValidExtensionStatement.yang");
+
+        assertThat((node instanceof YangModule), is(true));
+
+        // Check whether the node type is set properly to module.
+        assertThat(node.getNodeType(), is(YangNodeType.MODULE_NODE));
+
+        YangModule yangNode = (YangModule) node;
+        assertThat(yangNode.getName(), is("ietf-yang-compiler-annotation"));
+
+        YangExtension extension = yangNode.getExtensionList().iterator().next();
+        assertThat(extension.getName(), is("compiler-annotation"));
+        assertThat(extension.getArgumentName(), is("target"));
+        assertThat(extension.getDescription(), is("\"This extension allows for defining compiler annotations\""));
+    }
+}
+
diff --git a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/plugin/manager/InterFileLinkingTest.java b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/plugin/manager/InterFileLinkingTest.java
index 8052f30..7379074 100644
--- a/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/plugin/manager/InterFileLinkingTest.java
+++ b/utils/yangutils/plugin/src/test/java/org/onosproject/yangutils/plugin/manager/InterFileLinkingTest.java
@@ -16,13 +16,19 @@
 
 package org.onosproject.yangutils.plugin.manager;
 
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.ListIterator;
 import org.apache.maven.plugin.MojoExecutionException;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
+import org.onosproject.yangutils.datamodel.YangAugment;
+import org.onosproject.yangutils.datamodel.YangContainer;
 import org.onosproject.yangutils.datamodel.YangDerivedInfo;
 import org.onosproject.yangutils.datamodel.YangGrouping;
 import org.onosproject.yangutils.datamodel.YangLeaf;
+import org.onosproject.yangutils.datamodel.YangList;
 import org.onosproject.yangutils.datamodel.YangModule;
 import org.onosproject.yangutils.datamodel.YangNode;
 import org.onosproject.yangutils.datamodel.YangNodeType;
@@ -36,10 +42,6 @@
 import org.onosproject.yangutils.utils.io.impl.YangFileScanner;
 import org.onosproject.yangutils.utils.io.impl.YangPluginConfig;
 
-import java.io.IOException;
-import java.util.Iterator;
-import java.util.ListIterator;
-
 import static org.hamcrest.CoreMatchers.nullValue;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.Is.is;
@@ -779,4 +781,60 @@
         assertThat(referredNode1.getName(), is("module2"));
         assertThat(referredNode1.getPriority(), is(3));
     }
+
+    /**
+     * Checks contents of uses are copied as child of grouping.
+     */
+    @Test
+    public void usesInsideChildOfGrouping()
+            throws IOException, ParserException, MojoExecutionException {
+
+        String searchDir = "src/test/resources/usesInsideChildOfGrouping";
+        utilManager.createYangFileInfoSet(YangFileScanner.getYangFiles(searchDir));
+        utilManager.parseYangFileInfoSet();
+        utilManager.resolveDependenciesUsingLinker();
+
+        YangNode selfNode = null;
+        YangNode refNode1 = null;
+
+        for (YangNode rootNode : utilManager.getYangNodeSet()) {
+            if (rootNode.getName().equals("ietf-network")) {
+                selfNode = rootNode;
+            } else if (rootNode.getName().equals("ietf-te-topology")) {
+                refNode1 = rootNode;
+            }
+        }
+
+        // Check whether the data model tree returned is of type module.
+        assertThat(selfNode instanceof YangModule, is(true));
+        assertThat(selfNode.getNodeType(), is(MODULE_NODE));
+        YangModule yangNode = (YangModule) selfNode;
+        assertThat(yangNode.getName(), is("ietf-network"));
+
+        YangModule refNode = (YangModule) refNode1;
+        assertThat(refNode.getName(), is("ietf-te-topology"));
+
+        YangAugment augment = ((YangAugment) refNode.getChild().getNextSibling().
+                getNextSibling().getNextSibling().getNextSibling());
+        assertThat(augment.getName(), is("/nw:networks/nw:network/nw:node"));
+
+        YangUses uses = ((YangUses) augment.getChild());
+        YangContainer container = ((YangContainer) uses.getNextSibling());
+        assertThat(container.getName(), is("te"));
+
+        container = ((YangContainer) container.getChild());
+        assertThat(container.getName(), is("config"));
+
+        uses = ((YangUses) container.getChild().getNextSibling());
+        assertThat(uses.getName(), is("te-node-config-attributes"));
+
+        YangContainer container1 = ((YangContainer) uses.getNextSibling());
+        assertThat(container1.getName(), is("te-node-attributes"));
+
+        uses = ((YangUses) container1.getChild());
+        assertThat(uses.getName(), is("te-node-connectivity-matrix"));
+
+        YangList list = ((YangList) uses.getNextSibling());
+        assertThat(list.getName(), is("connectivity-matrix"));
+    }
 }
diff --git a/utils/yangutils/plugin/src/test/resources/CaseSubStatementOfAugment.yang b/utils/yangutils/plugin/src/test/resources/CaseSubStatementOfAugment.yang
new file mode 100644
index 0000000..7123f91
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/resources/CaseSubStatementOfAugment.yang
@@ -0,0 +1,58 @@
+module event {
+
+    namespace "http://example.com/event";
+    prefix "ev";
+
+    augment /snmp:snmp/snmp:engine/snmp:listen/snmp:transport {
+    if-feature tlstm;
+    case tls {
+      container tls {
+        description
+          "A list of IPv4 and IPv6 addresses and ports to which the
+           engine listens for SNMP messages over TLS.";
+        leaf ip {
+          type inet:ip-address;
+          mandatory true;
+          description
+            "The IPv4 or IPv6 address on which the engine listens
+             for SNMP messages over TLS.";
+        }
+        leaf port {
+          type inet:port-number;
+          description
+            "The TCP port on which the engine listens for SNMP
+             messages over TLS.
+             If the port is not configured, an engine that
+             acts as a Command Responder uses port 10161, and
+             an engine that acts as a Notification Receiver
+             uses port 10162.";
+        }
+      }
+    }
+    case dtls {
+      container dtls1 {
+        description
+          "A list of IPv4 and IPv6 addresses and ports to which the
+           engine listens for SNMP messages over DTLS.";
+        leaf ip {
+          type inet:ip-address;
+          mandatory true;
+          description
+            "The IPv4 or IPv6 address on which the engine listens
+             for SNMP messages over DTLS.";
+        }
+        leaf port {
+          type inet:port-number;
+          description
+            "The UDP port on which the engine listens for SNMP
+             messages over DTLS.
+             If the port is not configured, an engine that
+             acts as a Command Responder uses port 10161, and
+             an engine that acts as a Notification Receiver
+             uses port 10162.";
+        }
+      }
+    }
+  }
+}
+
diff --git a/utils/yangutils/plugin/src/test/resources/ValidExtensionStatement.yang b/utils/yangutils/plugin/src/test/resources/ValidExtensionStatement.yang
new file mode 100644
index 0000000..ca134fa
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/resources/ValidExtensionStatement.yang
@@ -0,0 +1,36 @@
+module ietf-yang-compiler-annotation {
+
+   namespace "urn:ietf:params:xml:ns:yang:ietf-yang-compiler-annotation";
+
+   prefix "ca";
+
+   organization
+     "IETF NETMOD (NETCONF Data Modeling Language) Working Group";
+
+   contact
+     "WG Web:   <http://tools.ietf.org/wg/netmod/>
+      WG List:  <mailto:netmod@ietf.org>";
+
+   description
+     "This YANG module defines an extension statement that allows for
+      defining compiler annotations.
+
+      The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
+      NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
+      'OPTIONAL' in the module text are to be interpreted as described
+      in RFC 2119 (http://tools.ietf.org/html/rfc2119).";
+
+     revision 2016-07-08 {
+     description
+       "Initial revision.";
+     reference
+       "draft-agv-netmod-yang-compiler-metadata:
+        Defining and Using compiler annotations with YANG";
+     }
+
+     extension compiler-annotation {
+        argument target;
+        description "This extension allows for defining compiler annotations";
+      } // compiler-annotation
+   } //module agv-yang-compiler-annotation
+
diff --git a/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-network.yang b/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-network.yang
new file mode 100644
index 0000000..8fb2bc0
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-network.yang
@@ -0,0 +1,28 @@
+module ietf-network {
+    yang-version 1;
+    namespace "urn:ietf:params:xml:ns:yang:ietf-network";
+    prefix nd;
+
+    revision 2015-12-08 {
+       description
+         "Initial revision.
+          NOTE TO RFC EDITOR: Please replace the following reference
+          to draft-ietf-i2rs-yang-network-topo-02 with
+          RFC number when published (i.e. RFC xxxx).";
+    }
+
+    container networks {
+        list network {
+            key "network-id";
+            leaf network-id {
+                type string;
+            }
+            list node {
+                key "node-id";
+                leaf node-id {
+                    type string;
+                }
+            }
+        }
+    }
+}
diff --git a/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-te-topology.yang b/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-te-topology.yang
new file mode 100644
index 0000000..f1776fb
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/resources/usesInsideChildOfGrouping/ietf-te-topology.yang
@@ -0,0 +1,60 @@
+module ietf-te-topology {
+    yang-version 1;
+    namespace "urn:ietf:params:xml:ns:yang:ietf-te-topology";
+
+    prefix "tet";
+
+    import ietf-network {
+        prefix "nw";
+    }
+
+    revision "2016-03-17" {
+        description "Initial revision";
+    }
+
+    grouping te-node-augment {
+        container te {
+            presence "TE support.";
+
+            leaf te-node-id {
+                type string;
+                mandatory true;
+            }
+
+            container config {
+                uses te-node-config;
+            } // config
+        } // te
+    } // te-node-augment
+
+    grouping te-node-config {
+        leaf-list te-node-template {
+            if-feature template;
+            type string;
+        }
+        uses te-node-config-attributes;
+    } // te-node-config
+
+    grouping te-node-config-attributes {
+        container te-node-attributes {
+            leaf admin-status {
+               type string;
+            }
+            uses te-node-connectivity-matrix;
+        } // te-node-attributes
+    } // te-node-config-attributes
+
+    grouping te-node-connectivity-matrix {
+        list connectivity-matrix {
+            key "id";
+            leaf id {
+                type uint32;
+                description "Identifies the connectivity-matrix entry.";
+            }
+        }
+    } // te-node-connectivity-matrix
+
+    augment "/nw:networks/nw:network/nw:node" {
+        uses te-node-augment;
+    }
+}