diff --git a/src/main/java/net/onrc/onos/util/GraphDBConnection.java b/src/main/java/net/onrc/onos/util/GraphDBConnection.java
index 9a50f47..1cc4e5a 100644
--- a/src/main/java/net/onrc/onos/util/GraphDBConnection.java
+++ b/src/main/java/net/onrc/onos/util/GraphDBConnection.java
@@ -43,6 +43,11 @@
 	}
 
 	/* Static 'instance' method */
+	/**
+	 * Get the instance of GraphDBConnection class.
+	 * @param conf the path to the database configuration file.
+	 * @return GraphDBConnection instance.
+	 */
 	public static synchronized GraphDBConnection getInstance(final String conf) {
 		if (GraphDBConnection.configFile == null
 				|| GraphDBConnection.configFile.isEmpty()) {
@@ -79,6 +84,9 @@
 		return singleton;
 	}
 
+	/** 
+	 * Get a FramedGraph instance of the graph.
+	 */
 	public FramedGraph<TitanGraph> getFramedGraph() {
 		if (isValid()) {
 			FramedGraph<TitanGraph> fg = new FramedGraph<TitanGraph>(graph);
@@ -89,6 +97,10 @@
 		}
 	}
 
+	/**
+	 * Get EventTransactionalGraph of the titan graph.
+	 * @return EventTransactionalGraph of the titan graph
+	 */
 	protected EventTransactionalGraph<TitanGraph> getEventGraph() {
 		if (isValid()) {
 			return eg;
@@ -97,16 +109,25 @@
 		}
 	}
 
+	/**
+	 * Add LocalGraphChangedLister for the graph.
+	 */
 	public void addEventListener(final LocalGraphChangedListener listener) {
 		EventTransactionalGraph<TitanGraph> eg = this.getEventGraph();
 		eg.addListener(listener);
 		log.debug("Registered listener {}", listener.getClass());
 	}
 
+	/**
+	 * Return whether this connection is valid.
+	 */
 	public Boolean isValid() {
 		return (graph != null || graph.isOpen());
 	}
 
+	/**
+	 * Commit changes for the graph operations.
+	 */
 	public void commit() {
 		try {
 			graph.commit();
@@ -116,6 +137,9 @@
 		}
 	}
 
+	/**
+	 * Rollback changes for the graph operations.
+	 */
 	public void rollback() {
 		try {
 			graph.rollback();
@@ -125,6 +149,9 @@
 		}
 	}
 
+	/**
+	 * Close this database connection.
+	 */
 	public void close() {
 		commit();
 	}
diff --git a/src/main/java/net/onrc/onos/util/GraphDBOperation.java b/src/main/java/net/onrc/onos/util/GraphDBOperation.java
index f939a3d..92157fb 100644
--- a/src/main/java/net/onrc/onos/util/GraphDBOperation.java
+++ b/src/main/java/net/onrc/onos/util/GraphDBOperation.java
@@ -332,18 +332,30 @@
 		fg.removeVertex(flowEntry.asVertex());
 	}
 	
+	/**
+	 * Get the instance of GraphDBConnection assigned to this class.
+	 */
 	public IDBConnection getDBConnection() {
 		return conn;
 	}
 	
+	/**
+	 * Commit changes for the graph.
+	 */
 	public void commit() {
 		conn.commit();
 	}
-	
+
+	/**
+	 * Rollback changes for the graph.
+	 */
 	public void rollback() {
 		conn.rollback();
 	}
 
+	/**
+	 * Close the connection of the assigned GraphDBConnection.
+	 */
 	public void close() {
 		conn.close();
 	}