[ONOS-4694] YANG management system outline and YMSM/YDT interfaces

Change-Id: I050ed98ba18edc2c2cea2abafeee6d8c9061b579
diff --git a/apps/yms/api/src/main/java/org/onosproject/yms/ynh/YangNotificationService.java b/apps/yms/api/src/main/java/org/onosproject/yms/ynh/YangNotificationService.java
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index 0000000..1beb498
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+/*
+ * 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.yms.ynh;
+
+/**
+ * Abstraction of an entity which provides interfaces to YANG notification
+ * service. YNH handles notification from the application/core and provide
+ * it to the protocols.
+ * <p>
+ * NBI Protocols which can support notification delivery for application(s)
+ * needs to add themselves as a listeners with YANG notification service.
+ * Protocols can use YANG notification service to check if a received
+ * notification should be filtered against any of their protocol specific
+ * filtering mechanism.
+ */
+public interface YangNotificationService {
+    //TODO
+}