M. Boger, T. Sturm, and P. Fragemann. Proc. Int'l Conf. eXtreme Programming and Flexible Processes in Software Engineering (XP), page 77--81. (2002)Alghero, Sardinia, Italy.
R. Straeten, T. Mens, J. Simmonds, and V. Jonckers. UML 2003 - The Unified Modeling Language, volume 2863 of Lecture Notes in Computer Science, page 326--340. Springer-Verlag, (2003)