[ONOS-3892] implement YANG leaf data model

Change-Id: I996d4d3d60a0ad2142e173c6ba26c9cc355ccc80
diff --git a/src/main/java/org/onosproject/yangutils/datamodel/YangImport.java b/src/main/java/org/onosproject/yangutils/datamodel/YangImport.java
new file mode 100644
index 0000000..cf18a62
--- /dev/null
+++ b/src/main/java/org/onosproject/yangutils/datamodel/YangImport.java
@@ -0,0 +1,176 @@
+/*
+ * Copyright 2016 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 org.onosproject.yangutils.datamodel.exceptions.DataModelException;
+import org.onosproject.yangutils.parser.Parsable;
+import org.onosproject.yangutils.parser.ParsableDataType;
+
+/*
+ *  Reference:RFC 6020.
+ *  The "import" statement makes definitions from one module available
+ *  inside another module or submodule.  The argument is the name of the
+ *  module to import, and the statement is followed by a block of
+ *  sub statements that holds detailed import information.
+ *  When a module is imported, the importing module may:
+ *  o  use any grouping and typedef defined at the top level in the
+ *     imported module or its submodules.
+ *
+ *  o  use any extension, feature, and identity defined in the imported
+ *     module or its submodules.
+ *
+ *  o  use any node in the imported module's schema tree in "must",
+ *     "path", and "when" statements, or as the target node in "augment"
+ *     and "deviation" statements.
+ *
+ *  The mandatory "prefix" sub statement assigns a prefix for the imported
+ *  module that is scoped to the importing module or submodule.  Multiple
+ *  "import" statements may be specified to import from different
+ *  modules.
+ *  When the optional "revision-date" sub-statement is present, any
+ *  typedef, grouping, extension, feature, and identity referenced by
+ *  definitions in the local module are taken from the specified revision
+ *  of the imported module.  It is an error if the specified revision of
+ *  the imported module does not exist.  If no "revision-date"
+ *  sub-statement is present, it is undefined from which revision of the
+ *  module they are taken.
+ *
+ *  Multiple revisions of the same module MUST NOT be imported.
+ *
+ *                       The import's Substatements
+ *
+ *                +---------------+---------+-------------+------------------+
+ *                | substatement  | section | cardinality |data model mapping|
+ *                +---------------+---------+-------------+------------------+
+ *                | prefix        | 7.1.4   | 1           | string           |
+ *                | revision-date | 7.1.5.1 | 0..1        | string           |
+ *                +---------------+---------+-------------+------------------+
+ */
+/**
+ * Maintains the information about the imported modules.
+ */
+public class YangImport implements Parsable {
+
+    /**
+     * Name of the module that is being imported.
+     */
+    private String name;
+
+    /**
+     * Prefix used to identify the entities from the imported module.
+     */
+    private String prefixId;
+
+    /**
+     * Reference:RFC 6020.
+     * The import's "revision-date" statement is used to specify the exact
+     * version of the module to import. The "revision-date" statement MUST match
+     * the most recent "revision" statement in the imported module. organization
+     * which defined the YANG module.
+     */
+    private String revision;
+
+    /**
+     * Default constructor.
+     */
+    public YangImport() {
+
+    }
+
+    /**
+     * Get the imported module name.
+     *
+     * @return the module name.
+     */
+    public String getModuleName() {
+        return name;
+    }
+
+    /**
+     * Set module name.
+     *
+     * @param moduleName the module name to set
+     */
+    public void setModuleName(String moduleName) {
+        name = moduleName;
+    }
+
+    /**
+     * Get the prefix used to identify the entities from the imported module.
+     *
+     * @return the prefix used to identify the entities from the imported
+     *         module.
+     */
+    public String getPrefixId() {
+        return prefixId;
+    }
+
+    /**
+     * Set prefix identifier.
+     *
+     * @param prefixId set the prefix identifier of the imported module.
+     */
+    public void setPrefixId(String prefixId) {
+        this.prefixId = prefixId;
+    }
+
+    /**
+     * Get the revision of the imported module.
+     *
+     * @return the revision of the imported module.
+     */
+    public String getRevision() {
+        return revision;
+    }
+
+    /**
+     * Set the revision of the imported module.
+     *
+     * @param rev set the revision of the imported module.
+     */
+    public void setRevision(String rev) {
+        revision = rev;
+    }
+
+    /**
+     * Returns the type of the parsed data.
+     *
+     * @return returns IMPORT_DATA
+     */
+    public ParsableDataType getParsableDataType() {
+        return ParsableDataType.IMPORT_DATA;
+    }
+
+    /**
+     * Validate the data on entering the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules
+     */
+    public void validateDataOnEntry() throws DataModelException {
+        // TODO auto-generated method stub, to be implemented by parser
+
+    }
+
+    /**
+     * Validate the data on exiting the corresponding parse tree node.
+     *
+     * @throws DataModelException a violation of data model rules
+     */
+    public void validateDataOnExit() throws DataModelException {
+        // TODO auto-generated method stub, to be implemented by parser
+
+    }
+}