C. Ahlberg, C. Williamson, and B. Shneiderman. CHI '92: Proceedings of the SIGCHI conference on Human factors in computing systems, page 619--626. New York, NY, USA, ACM Press, (1992)
D. Akehurst, and B. Bordbar. International Conference on the Unified Modeling Language (UML), 2185/2001, page 91-103. Toronto, (October 2001)Dated; refers to OCL 1. Most suggestions have been implemented in OCL 2..
A. Alashqur, S. Su, and H. Lam. VLDB '89: International Conference on Very Large Databases, page 433--442. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (1989)