public void WriteXMI(string filename)
 {
     System.Console.WriteLine ("Serialization: STARTING");
     SerializationDriver ser = new SerializationDriver ();
     ser.AddSerializer (new ExpertCoder.Uml2.Serialization.Serializer ());
     ser.Serialize (_xmiElements, filename);
     System.Console.WriteLine ("Serialization: DONE");
 }