1. Object Management Group (OMG): Object Constraint Language, Version 2.0 (2006)
2. Object Management Group (OMG): Meta Object Facility (MOF) Core Specification, Version 2.0 (2006)
3. Technische Universität Dresden, Department of Computer Science: (Dresden OCL Toolkit),
http://dresden-ocl.sourceforge.net
4. University of Kent at Canterbury, Department of Computing: (Kent Object Constraint Language Library),
http://www.cs.kent.ac.uk/projects/ocl
5. Kappel, G., Kapsammer, E., Kargl, H., Kramler, G., Reiter, T., Retschitzegger, W., Schwinger, W., Wimmer, M.: On Models and Ontologies - A Layered Approach for Model-based Tool Integration. In: Mayr, H.C., Breu, R. (eds.) Proceedings of Modellierung 2006, GI-Edition, Innsbruck, Austria, March 22-24, 2006. Lecture Notes in Informatics (2006)