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