Jean Bézivin Thomas Baar Tracy Gardner Martin Gogolla Reiner Hähnle Heinrich Hußmann Octavian Patrascoiu Peter H. Schmitt Jos Warmer OCL and Model Driven Engineering. 67-75 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3297&spage=67 2004 conf/uml/2004ml UML Satellite Activities db/conf/uml/ml2004.html#BezivinBGGHHPSW04