P. Martin. Proceedings of the 11th International Conference on Conceptual Structures (ICCS 2003), volume 2746 of Lecture Notes in Computer Science, page 160-173. Springer, (2003)
U. Priss, and L. Old. Proceedings of the 14th International Conference on Conceptual Structures (ICCS 2006), volume 4068 of Lecture Notes in Computer Science, page 388-400. Springer, (2006)