L. Mandel, and M. Victoria. World Congress on Formal Methods, 1708/1999, page 713. Toulouse, France, (September 1999)Dated as it refers to OCL 1, which lacked tuples.
A. Evans, R. France, K. Lano, and B. Rumpe. &\#171;UML&\#187; '98: Selected papers from the First International Workshop on The Unified Modeling Language &\#171;UML&\#187;'98, page 336--348. London, UK, Springer-Verlag, (1999)