diff --git a/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java b/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java
index 107c2f1..b566464 100644
--- a/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/antlrgencode/GeneratedYangListener.java
@@ -1178,22 +1178,6 @@
 
     /**
      * Enter a parse tree produced by GeneratedYangParser for grammar rule
-     * maxValueArgument.
-     *
-     * @param currentContext current context in the parsed tree
-     */
-    void enterMaxValueArgument(GeneratedYangParser.MaxValueArgumentContext currentContext);
-
-    /**
-     * Exit a parse tree produced by GeneratedYangParser for grammar rule
-     * maxValueArgument.
-     *
-     * @param currentContext current context in the parsed tree
-     */
-    void exitMaxValueArgument(GeneratedYangParser.MaxValueArgumentContext currentContext);
-
-    /**
-     * Enter a parse tree produced by GeneratedYangParser for grammar rule
      * valueStatement.
      *
      * @param currentContext current context in the parsed tree
@@ -1720,6 +1704,37 @@
      */
     void exitIdentifier(GeneratedYangParser.IdentifierContext currentContext);
 
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * version.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterVersion(GeneratedYangParser.VersionContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * version.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitVersion(GeneratedYangParser.VersionContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * range.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRange(GeneratedYangParser.RangeContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * range.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRange(GeneratedYangParser.RangeContext currentContext);
 
     /**
      * Enter a parse tree produced by GeneratedYangParser for grammar rule
@@ -1736,4 +1751,244 @@
      * @param currentContext current context in the parsed tree
      */
     void exitDateArgumentString(GeneratedYangParser.DateArgumentStringContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * length.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterLength(GeneratedYangParser.LengthContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * length.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitLength(GeneratedYangParser.LengthContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * path.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPath(GeneratedYangParser.PathContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * path.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPath(GeneratedYangParser.PathContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * position.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterPosition(GeneratedYangParser.PositionContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * position.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitPosition(GeneratedYangParser.PositionContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * status.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterStatus(GeneratedYangParser.StatusContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * status.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitStatus(GeneratedYangParser.StatusContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * config.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterConfig(GeneratedYangParser.ConfigContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * config.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitConfig(GeneratedYangParser.ConfigContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * mandatory.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMandatory(GeneratedYangParser.MandatoryContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * mandatory.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMandatory(GeneratedYangParser.MandatoryContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * ordered-by.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterOrderedBy(GeneratedYangParser.OrderedByContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * ordered-by.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitOrderedBy(GeneratedYangParser.OrderedByContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * min elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMinValue(GeneratedYangParser.MinValueContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * min elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMinValue(GeneratedYangParser.MinValueContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * max elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterMaxValue(GeneratedYangParser.MaxValueContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * max elements value.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitMaxValue(GeneratedYangParser.MaxValueContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * key.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterKey(GeneratedYangParser.KeyContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * key.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitKey(GeneratedYangParser.KeyContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * unique.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterUnique(GeneratedYangParser.UniqueContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * unique.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitUnique(GeneratedYangParser.UniqueContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * refine.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterRefine(GeneratedYangParser.RefineContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * refine.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitRefine(GeneratedYangParser.RefineContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterAugment(GeneratedYangParser.AugmentContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * augment.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitAugment(GeneratedYangParser.AugmentContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterDeviation(GeneratedYangParser.DeviationContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * deviation.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitDeviation(GeneratedYangParser.DeviationContext currentContext);
+
+    /**
+     * Enter a parse tree produced by GeneratedYangParser for grammar rule
+     * yang construct.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void enterYangConstruct(GeneratedYangParser.YangConstructContext currentContext);
+
+    /**
+     * Exit a parse tree produced by GeneratedYangParser for grammar rule
+     * yang construct.
+     *
+     * @param currentContext current context in the parsed tree
+     */
+    void exitYangConstruct(GeneratedYangParser.YangConstructContext currentContext);
 }
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
index 7027dc0..11ed0e4 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/TreeWalkListener.java
@@ -833,16 +833,6 @@
     }
 
     @Override
-    public void enterMaxValueArgument(GeneratedYangParser.MaxValueArgumentContext ctx) {
-        // TODO: implement the method.
-    }
-
-    @Override
-    public void exitMaxValueArgument(GeneratedYangParser.MaxValueArgumentContext ctx) {
-        // TODO: implement the method.
-    }
-
-    @Override
     public void enterValueStatement(GeneratedYangParser.ValueStatementContext ctx) {
         ValueListener.processValueEntry(this, ctx);
     }
@@ -1183,6 +1173,176 @@
     }
 
     @Override
+    public void enterRange(GeneratedYangParser.RangeContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitRange(GeneratedYangParser.RangeContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterLength(GeneratedYangParser.LengthContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitLength(GeneratedYangParser.LengthContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterPath(GeneratedYangParser.PathContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitPath(GeneratedYangParser.PathContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterPosition(GeneratedYangParser.PositionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitPosition(GeneratedYangParser.PositionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterStatus(GeneratedYangParser.StatusContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitStatus(GeneratedYangParser.StatusContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterConfig(GeneratedYangParser.ConfigContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitConfig(GeneratedYangParser.ConfigContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterMandatory(GeneratedYangParser.MandatoryContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitMandatory(GeneratedYangParser.MandatoryContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterOrderedBy(GeneratedYangParser.OrderedByContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitOrderedBy(GeneratedYangParser.OrderedByContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterMinValue(GeneratedYangParser.MinValueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitMinValue(GeneratedYangParser.MinValueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterMaxValue(GeneratedYangParser.MaxValueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitMaxValue(GeneratedYangParser.MaxValueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterKey(GeneratedYangParser.KeyContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitKey(GeneratedYangParser.KeyContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterUnique(GeneratedYangParser.UniqueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitUnique(GeneratedYangParser.UniqueContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterRefine(GeneratedYangParser.RefineContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitRefine(GeneratedYangParser.RefineContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterAugment(GeneratedYangParser.AugmentContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitAugment(GeneratedYangParser.AugmentContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterDeviation(GeneratedYangParser.DeviationContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitDeviation(GeneratedYangParser.DeviationContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterYangConstruct(GeneratedYangParser.YangConstructContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitYangConstruct(GeneratedYangParser.YangConstructContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void enterVersion(GeneratedYangParser.VersionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
+    public void exitVersion(GeneratedYangParser.VersionContext ctx) {
+        // TODO: implement the method.
+    }
+
+    @Override
     public void visitTerminal(TerminalNode terminalNode) {
         // TODO: implement the method.
     }
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java
index 68d2b43..ea4d20f 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListener.java
@@ -25,6 +25,7 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidBooleanValue;
 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;
@@ -42,7 +43,8 @@
  * config-arg          = true-keyword / false-keyword
  *
  * ANTLR grammar rule
- * configStatement : CONFIG_KEYWORD (TRUE_KEYWORD | FALSE_KEYWORD) STMTEND;
+ * configStatement : CONFIG_KEYWORD config STMTEND;
+ * config          : string;
  */
 
 /**
@@ -66,14 +68,11 @@
      */
     public static void processConfigEntry(TreeWalkListener listener,
             GeneratedYangParser.ConfigStatementContext ctx) {
-        boolean isConfig = false;
 
         // Check for stack to be non empty.
         checkStackIsNotEmpty(listener, MISSING_HOLDER, CONFIG_DATA, "", ENTRY);
 
-        if (ctx.TRUE_KEYWORD() != null) {
-            isConfig = true;
-        }
+        boolean isConfig = getValidBooleanValue(ctx.config().getText(), CONFIG_DATA, ctx);
 
         Parsable tmpData = listener.getParsedDataStack().peek();
         switch (tmpData.getYangConstructType()) {
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java
index d3472aa..8ec7883 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/KeyListener.java
@@ -24,6 +24,7 @@
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
 import static org.onosproject.yangutils.utils.YangConstructType.KEY_DATA;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
 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.ListenerErrorMessageConstruction.constructExtendedListenerErrorMessage;
@@ -39,7 +40,8 @@
  * key-stmt            = key-keyword sep key-arg-str stmtend
  *
  * ANTLR grammar rule
- * keyStatement : KEY_KEYWORD string STMTEND;
+ * keyStatement : KEY_KEYWORD key STMTEND;
+ * key          : string;
  */
 
 /**
@@ -66,12 +68,12 @@
                                          GeneratedYangParser.KeyStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, KEY_DATA, ctx.string().getText(), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, KEY_DATA, ctx.key().getText(), ENTRY);
 
         Parsable tmpData = listener.getParsedDataStack().peek();
         if (listener.getParsedDataStack().peek() instanceof YangList) {
             YangList yangList = (YangList) tmpData;
-            String tmpKeyValue = ctx.string().getText().replace("\"", "");
+            String tmpKeyValue = removeQuotesAndHandleConcat(ctx.key().getText());
             if (tmpKeyValue.contains(" ")) {
                 String[] keyValues = tmpKeyValue.split(" ");
                 for (String keyValue : keyValues) {
@@ -79,7 +81,7 @@
                         yangList.addKey(keyValue);
                     } catch (DataModelException e) {
                         throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA, KEY_DATA,
-                                ctx.string().getText(), ENTRY, e.getMessage()));
+                                ctx.key().getText(), ENTRY, e.getMessage()));
                     }
                 }
             } else {
@@ -87,11 +89,11 @@
                     yangList.addKey(tmpKeyValue);
                 } catch (DataModelException e) {
                     throw new ParserException(constructExtendedListenerErrorMessage(UNHANDLED_PARSED_DATA, KEY_DATA,
-                            ctx.string().getText(), ENTRY, e.getMessage()));
+                            ctx.key().getText(), ENTRY, e.getMessage()));
                 }
             }
         } else {
-            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, KEY_DATA, ctx.string().getText(),
+            throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, KEY_DATA, ctx.key().getText(),
                             ENTRY));
         }
     }
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java
index ea33cd7..3ca820c 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListener.java
@@ -22,6 +22,7 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidBooleanValue;
 import static org.onosproject.yangutils.utils.YangConstructType.MANDATORY_DATA;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
@@ -42,7 +43,8 @@
  *  mandatory-arg       = true-keyword / false-keyword
  *
  * ANTLR grammar rule
- *  mandatoryStatement : MANDATORY_KEYWORD (TRUE_KEYWORD | FALSE_KEYWORD) STMTEND;
+ *  mandatoryStatement : MANDATORY_KEYWORD mandatory STMTEND;
+ *  mandatory          : string;
  */
 
 /**
@@ -71,15 +73,13 @@
         // Check for stack to be non empty.
         checkStackIsNotEmpty(listener, MISSING_HOLDER, MANDATORY_DATA, "", ENTRY);
 
+        boolean isMandatory = getValidBooleanValue(ctx.mandatory().getText(), MANDATORY_DATA, ctx);
+
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getYangConstructType()) {
             case LEAF_DATA:
                 YangLeaf leaf = (YangLeaf) tmpNode;
-                if (ctx.TRUE_KEYWORD() != null) {
-                    leaf.setMandatory(true);
-                } else {
-                    leaf.setMandatory(false);
-                }
+                leaf.setMandatory(isMandatory);
                 break;
             case CHOICE_DATA: // TODO
                 break;
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
index da8a666..cae2433 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MaxElementsListener.java
@@ -22,11 +22,13 @@
 import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
+import org.onosproject.yangutils.utils.YangConstructType;
 
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
 import static org.onosproject.yangutils.utils.YangConstructType.MAX_ELEMENT_DATA;
 
@@ -40,7 +42,8 @@
  *                          max-value-arg >
  *
  * ANTLR grammar rule
- * maxElementsStatement :  MAX_ELEMENTS_KEYWORD maxValueArgument STMTEND;
+ * maxElementsStatement : MAX_ELEMENTS_KEYWORD maxValue STMTEND;
+ * maxValue             : string;
  */
 
 /**
@@ -50,6 +53,9 @@
  */
 public final class MaxElementsListener {
 
+    private static final String POSITIVE_INTEGER_PATTERN = "[1-9][0-9]*";
+    private static final String UNBOUNDED_KEYWORD = "unbounded";
+
     /**
      * Creates a new max-elements listener.
      */
@@ -65,16 +71,11 @@
      */
     public static void processMaxElementsEntry(TreeWalkListener listener,
             GeneratedYangParser.MaxElementsStatementContext ctx) {
-        int maxElementsValue;
 
         // Check for stack to be non empty.
         checkStackIsNotEmpty(listener, MISSING_HOLDER, MAX_ELEMENT_DATA, "", ENTRY);
 
-        if (ctx.maxValueArgument().UNBOUNDED_KEYWORD() != null) {
-            maxElementsValue = Integer.MAX_VALUE;
-        } else {
-            maxElementsValue = Integer.parseInt(ctx.maxValueArgument().INTEGER().getText());
-        }
+        int maxElementsValue = getValidMaxElementValue(ctx);
 
         Parsable tmpData = listener.getParsedDataStack().peek();
         switch (tmpData.getYangConstructType()) {
@@ -90,4 +91,31 @@
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MAX_ELEMENT_DATA, "", ENTRY));
         }
     }
+
+    /**
+     * Validates max element value and returns the value from context.
+     *
+     * @param ctx context object of the grammar rule
+     * @return max element's value
+     */
+    private static int getValidMaxElementValue(GeneratedYangParser.MaxElementsStatementContext ctx) {
+
+        int maxElementsValue;
+
+        String value = removeQuotesAndHandleConcat(ctx.maxValue().getText());
+        if (value.equals(UNBOUNDED_KEYWORD)) {
+            maxElementsValue = Integer.MAX_VALUE;
+        } else if (value.matches(POSITIVE_INTEGER_PATTERN)) {
+            maxElementsValue = Integer.parseInt(value);
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(MAX_ELEMENT_DATA) + " value " + value + " is not " +
+                    "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        return maxElementsValue;
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java
index a89c6ce..d14775b 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListener.java
@@ -23,6 +23,7 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNonNegativeIntegerValue;
 import static org.onosproject.yangutils.utils.YangConstructType.MIN_ELEMENT_DATA;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
@@ -41,7 +42,8 @@
  *  min-value-arg       = non-negative-integer-value
  *
  * ANTLR grammar rule
- * minElementsStatement : MIN_ELEMENTS_KEYWORD INTEGER STMTEND;
+ * minElementsStatement : MIN_ELEMENTS_KEYWORD minValue STMTEND;
+ * minValue             : string;
  */
 
 /**
@@ -68,21 +70,23 @@
                                                GeneratedYangParser.MinElementsStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, MIN_ELEMENT_DATA, ctx.INTEGER().getText(), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, MIN_ELEMENT_DATA, ctx.minValue().getText(), ENTRY);
+
+        int minElementValue = getValidNonNegativeIntegerValue(ctx.minValue().getText(), MIN_ELEMENT_DATA, ctx);
 
         Parsable tmpData = listener.getParsedDataStack().peek();
         switch (tmpData.getYangConstructType()) {
             case LEAF_LIST_DATA:
                 YangLeafList leafList = (YangLeafList) tmpData;
-                leafList.setMinElements(Integer.parseInt(ctx.INTEGER().getText()));
+                leafList.setMinElements(minElementValue);
                 break;
             case LIST_DATA:
                 YangList yangList = (YangList) tmpData;
-                yangList.setMinElements(Integer.parseInt(ctx.INTEGER().getText()));
+                yangList.setMinElements(minElementValue);
                 break;
             default:
                 throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, MIN_ELEMENT_DATA,
-                        ctx.INTEGER().getText(), ENTRY));
+                        ctx.minValue().getText(), ENTRY));
         }
     }
 }
\ No newline at end of file
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java
index a4a094b..f4d26cf 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/PositionListener.java
@@ -30,7 +30,8 @@
  * zero-integer-value  = 1*DIGIT
  *
  * ANTLR grammar rule
- * positionStatement : POSITION_KEYWORD string STMTEND;
+ * positionStatement : POSITION_KEYWORD position STMTEND;
+ * position          : string;
  */
 
 import org.onosproject.yangutils.datamodel.YangBit;
@@ -44,7 +45,7 @@
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
-import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidNonNegativeIntegerValue;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
 import static org.onosproject.yangutils.utils.YangConstructType.POSITION_DATA;
 
@@ -54,9 +55,6 @@
  */
 public final class PositionListener {
 
-    // Exact message in case position is invalid.
-    private static String errMsg;
-
     /**
      * Creates a new position listener.
      */
@@ -74,27 +72,20 @@
             GeneratedYangParser.PositionStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.string().getText(), ENTRY);
-
-        String position = removeQuotesAndHandleConcat(ctx.string().getText());
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY);
 
         // Obtain the node of the stack.
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getYangConstructType()) {
             case BIT_DATA: {
                 YangBit bitNode = (YangBit) tmpNode;
-                if (!isBitPositionValid(listener, ctx, position)) {
-                    ParserException parserException = new ParserException(errMsg);
-                    parserException.setLine(ctx.getStart().getLine());
-                    parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
-                    throw parserException;
-                }
-                bitNode.setPosition(Integer.valueOf(position));
+                int positionValue = getValidBitPosition(listener, ctx);
+                bitNode.setPosition(positionValue);
                 break;
             }
             default:
                 throw new ParserException(
-                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.string().getText(), ENTRY));
+                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY));
         }
     }
 
@@ -103,39 +94,38 @@
      *
      * @param listener Listener's object
      * @param ctx context object of the grammar rule
-     * @return validation result
+     * @return position value
      */
-    private static boolean isBitPositionValid(TreeWalkListener listener,
-            GeneratedYangParser.PositionStatementContext ctx, String position) {
+    private static int getValidBitPosition(TreeWalkListener listener,
+            GeneratedYangParser.PositionStatementContext ctx) {
         Parsable bitNode = listener.getParsedDataStack().pop();
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.string().getText(), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY);
 
-        if (Integer.valueOf(position) < 0) {
-            errMsg = "YANG file error: Negative value of position is invalid.";
-            listener.getParsedDataStack().push(bitNode);
-            return false;
-        }
+        int positionValue = getValidNonNegativeIntegerValue(ctx.position().getText(), POSITION_DATA, ctx);
 
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getYangConstructType()) {
             case BITS_DATA: {
                 YangBits yangBits = (YangBits) tmpNode;
                 for (YangBit curBit : yangBits.getBitSet()) {
-                    if (Integer.valueOf(position) == curBit.getPosition()) {
-                        errMsg = "YANG file error: Duplicate value of position is invalid.";
+                    if (positionValue == curBit.getPosition()) {
                         listener.getParsedDataStack().push(bitNode);
-                        return false;
+                        ParserException parserException = new ParserException("YANG file error: Duplicate value of " +
+                                "position is invalid.");
+                        parserException.setLine(ctx.getStart().getLine());
+                        parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+                        throw parserException;
                     }
                 }
                 listener.getParsedDataStack().push(bitNode);
-                return true;
+                return positionValue;
             }
             default:
                 listener.getParsedDataStack().push(bitNode);
                 throw new ParserException(
-                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.string().getText(), ENTRY));
+                        constructListenerErrorMessage(INVALID_HOLDER, POSITION_DATA, ctx.position().getText(), ENTRY));
         }
     }
 }
\ No newline at end of file
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java
index 379994e..b02371b 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/StatusListener.java
@@ -23,10 +23,12 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
 import static org.onosproject.yangutils.utils.YangConstructType.STATUS_DATA;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_HOLDER;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.INVALID_CONTENT;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorType.MISSING_HOLDER;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerValidation.checkStackIsNotEmpty;
 
@@ -51,6 +53,10 @@
  */
 public final class StatusListener {
 
+    private static final String CURRENT_KEYWORD = "current";
+    private static final String DEPRECATED_KEYWORD = "deprecated";
+    private static final String OBSOLETE_KEYWORD = "obsolete";
+
     /**
      * Creates a new status listener.
      */
@@ -67,18 +73,11 @@
      */
     public static void processStatusEntry(TreeWalkListener listener,
                                           GeneratedYangParser.StatusStatementContext ctx) {
-        YangStatusType status;
 
         // Check for stack to be non empty.
         checkStackIsNotEmpty(listener, MISSING_HOLDER, STATUS_DATA, "", ENTRY);
 
-        if (ctx.CURRENT_KEYWORD() != null) {
-            status = YangStatusType.CURRENT;
-        } else if (ctx.DEPRECATED_KEYWORD() != null) {
-            status = YangStatusType.DEPRECATED;
-        } else {
-            status = YangStatusType.OBSOLETE;
-        }
+        YangStatusType status = getValidStatus(ctx);
 
         Parsable tmpData = listener.getParsedDataStack().peek();
         if (tmpData instanceof YangStatus) {
@@ -88,4 +87,28 @@
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, STATUS_DATA, "", ENTRY));
         }
     }
+
+    /**
+     * Validates status value and returns the value from context.
+     *
+     * @param ctx context object of the grammar rule
+     * @return status current/deprecated/obsolete
+     */
+    private static YangStatusType getValidStatus(GeneratedYangParser.StatusStatementContext ctx) {
+
+        YangStatusType status;
+
+        String value = removeQuotesAndHandleConcat(ctx.status().getText());
+        if (value.equals(CURRENT_KEYWORD)) {
+            status = YangStatusType.CURRENT;
+        } else if (value.equals(DEPRECATED_KEYWORD)) {
+            status = YangStatusType.DEPRECATED;
+        } else if (value.equals(OBSOLETE_KEYWORD)) {
+            status = YangStatusType.OBSOLETE;
+        } else {
+            throw new ParserException(constructListenerErrorMessage(INVALID_CONTENT, STATUS_DATA, value, ENTRY));
+        }
+
+        return status;
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
index f8d5361..a421867 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/listeners/VersionListener.java
@@ -23,7 +23,7 @@
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 import org.onosproject.yangutils.parser.impl.TreeWalkListener;
 
-import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.removeQuotesAndHandleConcat;
+import static org.onosproject.yangutils.parser.impl.parserutils.ListenerUtil.getValidVersion;
 import static org.onosproject.yangutils.utils.YangConstructType.VERSION_DATA;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorLocation.ENTRY;
 import static org.onosproject.yangutils.parser.impl.parserutils.ListenerErrorMessageConstruction.constructListenerErrorMessage;
@@ -60,7 +60,8 @@
  * submodule_header_statement : yang_version_stmt? belongs_to_stmt
  *                            | belongs_to_stmt yang_version_stmt?
  *                            ;
- * yang_version_stmt :   YANG_VERSION_KEYWORD string STMTEND;
+ * yang_version_stmt : YANG_VERSION_KEYWORD version STMTEND;
+ * version           : string;
  */
 
 /**
@@ -86,42 +87,26 @@
                                            GeneratedYangParser.YangVersionStatementContext ctx) {
 
         // Check for stack to be non empty.
-        checkStackIsNotEmpty(listener, MISSING_HOLDER, VERSION_DATA, ctx.string().getText(), ENTRY);
+        checkStackIsNotEmpty(listener, MISSING_HOLDER, VERSION_DATA, ctx.version().getText(), ENTRY);
 
-        String version = removeQuotesAndHandleConcat(ctx.string().getText());
-        if (!isVersionValid(Integer.valueOf(version))) {
-            ParserException parserException = new ParserException("YANG file error: Input version not supported");
-            parserException.setLine(ctx.getStart().getLine());
-            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
-            throw parserException;
-        }
+        byte version = getValidVersion(ctx);
 
         // Obtain the node of the stack.
         Parsable tmpNode = listener.getParsedDataStack().peek();
         switch (tmpNode.getYangConstructType()) {
         case MODULE_DATA: {
             YangModule module = (YangModule) tmpNode;
-            module.setVersion((byte) 1);
+            module.setVersion(version);
             break;
         }
         case SUB_MODULE_DATA: {
             YangSubModule subModule = (YangSubModule) tmpNode;
-            subModule.setVersion((byte) 1);
+            subModule.setVersion(version);
             break;
         }
         default:
             throw new ParserException(constructListenerErrorMessage(INVALID_HOLDER, VERSION_DATA,
-                                                                    ctx.string().getText(), ENTRY));
+                                                                    ctx.version().getText(), ENTRY));
         }
     }
-
-    /**
-     * Validates whether the value of YANG version.
-     *
-     * @param version input yang version
-     * @return validation result
-     */
-    private static boolean isVersionValid(Integer version) {
-        return version == 1;
-    }
 }
diff --git a/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java b/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
index 41b2418..07c8105 100644
--- a/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
+++ b/src/main/java/org/onosproject/yangutils/parser/impl/parserutils/ListenerUtil.java
@@ -21,6 +21,8 @@
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.regex.Pattern;
+
+import org.onosproject.yangutils.parser.antlrgencode.GeneratedYangParser;
 import org.onosproject.yangutils.utils.YangConstructType;
 import org.onosproject.yangutils.parser.exceptions.ParserException;
 
@@ -29,7 +31,11 @@
  */
 public final class ListenerUtil {
     private static final Pattern IDENTIFIER_PATTERN = Pattern.compile("[a-zA-Z_][a-zA-Z0-9_.-]*");
+    private static final String NON_NEGATIVE_INTEGER_PATTERN = "[0-9]+";
     private static final String PLUS = "+";
+    private static final String ONE = "1";
+    private static final String TRUE_KEYWORD = "true";
+    private static final String FALSE_KEYWORD = "false";
     private static final int IDENTIFIER_LENGTH = 64;
 
     /**
@@ -109,4 +115,73 @@
 
         return true;
     }
+
+    /**
+     * Validates YANG version.
+     *
+     * @param ctx version context object of the grammar rule
+     * @return valid version
+     */
+    public static byte getValidVersion(GeneratedYangParser.YangVersionStatementContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(ctx.version().getText());
+        if (!value.equals(ONE)) {
+            ParserException parserException = new ParserException("YANG file error: Input version not supported");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        return Byte.valueOf(value);
+    }
+
+    /**
+     * Validates non negative integer value.
+     *
+     * @param integerValue integer to be validated
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx context object of the grammar rule
+     * @return valid non negative integer value
+     */
+    public static int getValidNonNegativeIntegerValue(String integerValue, YangConstructType yangConstruct,
+                                           ParserRuleContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(integerValue);
+        if (!value.matches(NON_NEGATIVE_INTEGER_PATTERN)) {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                    "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+
+        return Integer.parseInt(value);
+    }
+
+    /**
+     * Validates boolean value.
+     *
+     * @param booleanValue value to be validated
+     * @param yangConstruct yang construct for creating error message
+     * @param ctx context object of the grammar rule
+     * @return boolean value either true or false
+     */
+    public static boolean getValidBooleanValue(String booleanValue, YangConstructType yangConstruct,
+                                                ParserRuleContext ctx) {
+
+        String value = removeQuotesAndHandleConcat(booleanValue);
+        if (value.equals(TRUE_KEYWORD)) {
+            return true;
+        } else if (value.equals(FALSE_KEYWORD)) {
+            return false;
+        } else {
+            ParserException parserException = new ParserException("YANG file error : " +
+                    YangConstructType.getYangConstructType(yangConstruct) + " value " + value + " is not " +
+                    "valid.");
+            parserException.setLine(ctx.getStart().getLine());
+            parserException.setCharPosition(ctx.getStart().getCharPositionInLine());
+            throw parserException;
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/main/resources/GeneratedYang.g4 b/src/main/resources/GeneratedYang.g4
index 44b5c51..629929c 100644
--- a/src/main/resources/GeneratedYang.g4
+++ b/src/main/resources/GeneratedYang.g4
@@ -64,7 +64,6 @@
      *                       *(import-stmt stmtsep)
      *                       *(include-stmt stmtsep)
      */
-
     linkageStatements : (importStatement
                   | includeStatement)*;
 
@@ -75,7 +74,6 @@
      *                       [description-stmt stmtsep]
      *                       [reference-stmt stmtsep]
      */
-
     metaStatements : organizationStatement? contactStatement? descriptionStatement? referenceStatement?
                | organizationStatement? contactStatement? referenceStatement? descriptionStatement?
                | organizationStatement? descriptionStatement? contactStatement? referenceStatement?
@@ -117,7 +115,6 @@
      *                          notification-stmt /
      *                          deviation-stmt) stmtsep)
      */
-
     bodyStatements : (extensionStatement
                | featureStatement
                | identityStatement
@@ -134,8 +131,7 @@
      * yang-version-stmt   = yang-version-keyword sep yang-version-arg-str
      *                       optsep stmtend
      */
-
-    yangVersionStatement :   YANG_VERSION_KEYWORD string STMTEND;
+    yangVersionStatement :   YANG_VERSION_KEYWORD version STMTEND;
 
 
     /**
@@ -455,7 +451,7 @@
      *                             [reference-stmt stmtsep]
      *                          "}")
      */
-    rangeStatement : RANGE_KEYWORD string (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
+    rangeStatement : RANGE_KEYWORD range (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
 
     commonStatements : errorMessageStatement? errorAppTagStatement? descriptionStatement? referenceStatement?
                  | errorMessageStatement? errorAppTagStatement? referenceStatement? descriptionStatement?
@@ -501,7 +497,7 @@
      *                             [reference-stmt stmtsep]
      *                          "}")
      */
-    lengthStatement : LENGTH_KEYWORD string
+    lengthStatement : LENGTH_KEYWORD length
                   (STMTEND | LEFT_CURLY_BRACE commonStatements RIGHT_CURLY_BRACE);
 
     /**
@@ -577,7 +573,7 @@
     /**
      *  path-stmt           = path-keyword sep path-arg-str stmtend
      */
-    pathStatement : PATH_KEYWORD string STMTEND;
+    pathStatement : PATH_KEYWORD path STMTEND;
 
     /**
      *  require-instance-stmt = require-instance-keyword sep
@@ -657,7 +653,7 @@
      *                              position-value-arg >
      *  position-value-arg  = non-negative-integer-value
      */
-    positionStatement : POSITION_KEYWORD string STMTEND;
+    positionStatement : POSITION_KEYWORD position STMTEND;
 
     /**
      *  status-stmt         = status-keyword sep status-arg-str stmtend
@@ -667,7 +663,7 @@
      *                        obsolete-keyword /
      *                        deprecated-keyword
      */
-    statusStatement : STATUS_KEYWORD (CURRENT_KEYWORD | OBSOLETE_KEYWORD | DEPRECATED_KEYWORD) STMTEND;
+    statusStatement : STATUS_KEYWORD status STMTEND;
 
     /**
      *  config-stmt         = config-keyword sep
@@ -676,7 +672,7 @@
      *                          config-arg >
      *  config-arg          = true-keyword / false-keyword
      */
-    configStatement : CONFIG_KEYWORD (TRUE_KEYWORD | FALSE_KEYWORD) STMTEND;
+    configStatement : CONFIG_KEYWORD config STMTEND;
 
     /**
      *  mandatory-stmt      = mandatory-keyword sep
@@ -687,7 +683,7 @@
      *
      *  mandatory-arg       = true-keyword / false-keyword
      */
-    mandatoryStatement : MANDATORY_KEYWORD (TRUE_KEYWORD | FALSE_KEYWORD) STMTEND;
+    mandatoryStatement : MANDATORY_KEYWORD mandatory STMTEND;
 
     /**
      *  presence-stmt       = presence-keyword sep string stmtend
@@ -703,7 +699,7 @@
      *
      *  ordered-by-arg      = user-keyword / system-keyword
      */
-    orderedByStatement : ORDERED_BY_KEYWORD (USER_KEYWORD | SYSTEM_KEYWORD) STMTEND;
+    orderedByStatement : ORDERED_BY_KEYWORD orderedBy STMTEND;
 
     /**
      *  must-stmt           = must-keyword sep string optsep
@@ -735,22 +731,17 @@
      *                          min-value-arg >
      *  min-value-arg       = non-negative-integer-value
      */
-    minElementsStatement : MIN_ELEMENTS_KEYWORD INTEGER STMTEND;
+    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 >
-
-     */
-    maxElementsStatement :  MAX_ELEMENTS_KEYWORD maxValueArgument STMTEND;
-
-    /**
      *  max-value-arg       = unbounded-keyword /
      *                        positive-integer-value
      */
-    maxValueArgument : UNBOUNDED_KEYWORD | INTEGER;
+    maxElementsStatement :  MAX_ELEMENTS_KEYWORD maxValue STMTEND;
 
     /**
      *  value-stmt          = value-keyword sep integer-value stmtend
@@ -873,12 +864,12 @@
     /**
      *  key-stmt            = key-keyword sep key-arg-str stmtend
      */
-    keyStatement : KEY_KEYWORD string STMTEND;
+    keyStatement : KEY_KEYWORD key STMTEND;
 
     /**
      *  unique-stmt         = unique-keyword sep unique-arg-str stmtend
      */
-    uniqueStatement: UNIQUE_KEYWORD string STMTEND;
+    uniqueStatement: UNIQUE_KEYWORD unique STMTEND;
 
     /**
      *  choice-stmt         = choice-keyword sep identifier-arg-str optsep
@@ -958,9 +949,9 @@
      *                              refine-anyxml-stmts)
      *                         "}")
      */
-    refineStatement : REFINE_KEYWORD string (STMTEND  | LEFT_CURLY_BRACE (refineContainerStatements | refineLeafStatements
-                  | refineLeafListStatements | refineListStatements | refineChoiceStatements | refineCaseStatements)
-                  RIGHT_CURLY_BRACE);
+    refineStatement : REFINE_KEYWORD refine (STMTEND  | LEFT_CURLY_BRACE (refineContainerStatements
+                    | refineLeafStatements | refineLeafListStatements | refineListStatements | refineChoiceStatements
+                    | refineCaseStatements) RIGHT_CURLY_BRACE);
 
     /**
      *  refine-container-stmts =
@@ -1046,8 +1037,9 @@
      *                         "}"
      * TODO : 0..1 occurance to be checked in listener
      */
-    usesAugmentStatement : AUGMENT_KEYWORD string LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement | statusStatement
-                        | descriptionStatement | referenceStatement | dataDefStatement | caseStatement)* RIGHT_CURLY_BRACE;
+    usesAugmentStatement : AUGMENT_KEYWORD augment LEFT_CURLY_BRACE (whenStatement | ifFeatureStatement
+                         | statusStatement | descriptionStatement | referenceStatement | dataDefStatement
+                         | caseStatement)* RIGHT_CURLY_BRACE;
 
     /**
      *  augment-stmt        = augment-keyword sep augment-arg-str optsep
@@ -1158,9 +1150,9 @@
      *                        "}"
      * TODO : 0..1 occurance to be checked in listener
      */
-    deviationStatement: DEVIATION_KEYWORD string LEFT_CURLY_BRACE (descriptionStatement | referenceStatement
-                    | deviateNotSupportedStatement | deviateAddStatement | deviateReplaceStatement | deviateDeleteStatement)*
-                    RIGHT_CURLY_BRACE;
+    deviationStatement: DEVIATION_KEYWORD deviation LEFT_CURLY_BRACE (descriptionStatement | referenceStatement
+                      | deviateNotSupportedStatement | deviateAddStatement | deviateReplaceStatement
+                      | deviateDeleteStatement)* RIGHT_CURLY_BRACE;
 
     /**
      * deviate-not-supported-stmt =
@@ -1222,10 +1214,61 @@
 
     string : STRING (PLUS STRING)*
            | IDENTIFIER
-           | INTEGER;
+           | INTEGER
+           | yangConstruct;
 
     identifier : STRING (PLUS STRING)*
-               | IDENTIFIER;
+               | 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;
+
+    augment : string;
+
+    deviation : 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;
\ No newline at end of file
diff --git a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListenerTest.java b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListenerTest.java
index fe20cad..7e693d5 100644
--- a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListenerTest.java
+++ b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/ConfigListenerTest.java
@@ -115,7 +115,7 @@
     @Test
     public void processConfigInvalidValue() throws IOException, ParserException {
         thrown.expect(ParserException.class);
-        thrown.expectMessage("mismatched input 'invalid' expecting {'false', 'true'}");
+        thrown.expectMessage("YANG file error : config value invalid is not valid.");
         YangNode node = manager.getDataModel("src/test/resources/ConfigInvalidValue.yang");
     }
 
@@ -125,7 +125,7 @@
     @Test
     public void processConfigEmptyValue() throws IOException, ParserException {
         thrown.expect(ParserException.class);
-        thrown.expectMessage("missing {'false', 'true'} at ';'");
+        thrown.expectMessage("no viable alternative at input ';'");
         YangNode node = manager.getDataModel("src/test/resources/ConfigEmptyValue.yang");
     }
 
diff --git a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListenerTest.java b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListenerTest.java
index 05ee69a..bc27dad 100644
--- a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListenerTest.java
+++ b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MandatoryListenerTest.java
@@ -126,7 +126,7 @@
     @Test
     public void processMandatoryEmptyStatement() throws IOException, ParserException {
         thrown.expect(ParserException.class);
-        thrown.expectMessage("missing {'false', 'true'} at ';'");
+        thrown.expectMessage("no viable alternative at input ';'");
         YangNode node = manager.getDataModel("src/test/resources/MandatoryEmptyStatement.yang");
     }
 
diff --git a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListenerTest.java b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListenerTest.java
index b197557..7f4a6f6 100644
--- a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListenerTest.java
+++ b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/MinElementsListenerTest.java
@@ -111,7 +111,7 @@
     @Test
     public void processMinElementsInvalidValue() throws IOException, ParserException {
         thrown.expect(ParserException.class);
-        thrown.expectMessage("mismatched input 'asd' expecting INTEGER");
+        thrown.expectMessage("YANG file error : min-elements value asd is not valid.");
         YangNode node = manager.getDataModel("src/test/resources/MinElementsInvalidValue.yang");
     }
 
diff --git a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/StatusListenerTest.java b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/StatusListenerTest.java
index 6850425..984b0f2 100644
--- a/src/test/java/org/onosproject/yangutils/parser/impl/listeners/StatusListenerTest.java
+++ b/src/test/java/org/onosproject/yangutils/parser/impl/listeners/StatusListenerTest.java
@@ -141,7 +141,7 @@
     @Test
     public void processStatusInvalidValue() throws IOException, ParserException {
         thrown.expect(ParserException.class);
-        thrown.expectMessage("mismatched input 'invalid' expecting {'current', 'deprecated', 'obsolete'}");
+        thrown.expectMessage("Invalid content in status \"invalid\" before processing.");
         YangNode node = manager.getDataModel("src/test/resources/StatusInvalidValue.yang");
     }