[ONOS-4650][ONOS-4726][ONOS-4727] [ONOS-4728]Implement must parser + when parser + feature + if-feature + revision defect fix

Change-Id: I0a3aee6c1c6b72ef7da7f7f565fd0f149fe3fd42
diff --git a/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangMustHolder.java b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangMustHolder.java
new file mode 100644
index 0000000..badd3d9
--- /dev/null
+++ b/utils/yangutils/datamodel/src/main/java/org/onosproject/yangutils/datamodel/YangMustHolder.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.datamodel;
+
+import java.util.List;
+
+/**
+ * Abstraction of must entity. It is used to abstract the data holders of must.
+ */
+public interface YangMustHolder {
+
+    /**
+     * Returns the list of must from data holder like container / list.
+     *
+     * @return the list of must
+     */
+    List<YangMust> getListOfMust();
+
+    /**
+     * Sets the list of must.
+     *
+     * @param mustConstraintList the list of must to set
+     */
+    void setListOfMust(List<YangMust> mustConstraintList);
+
+    /**
+     * Adds must in data holder like container / list.
+     *
+     * @param must the must to be added
+     */
+    void addMust(YangMust must);
+}