M. Ribière, and R. Dieng-Kuntz. Proceedings of the 10th International Conference on Conceptual Structures (ICCS 2002), volume 2393 of Lecture Notes in Computer Science, page 220-234. Springer, (2002)
R. Bachmeyer, and H. Delugach. Proceedings of the 15th International Conference on Conceptual Structures (ICCS 2007), volume 4604 of Lecture Notes in Artificial Intelligence, page 179-191. Berlin, Heidelberg, Springer-Verlag, (July 2007)