Kenneth Baclawski Mieczyslaw M. Kokar Paul A. Kogut Lewis Hart Jeffrey E. Smith Jerzy Letkowski Pat Emery Extending the Unified Modeling Language for ontology development. 142-156 2002 1 Software and System Modeling 2 http://dx.doi.org/10.1007/s10270-002-0008-4 db/journals/sosym/sosym1.html#BaclawskiKKHSLE02