P. Buche, J. Dibie-Barthélemy, and G. Hignette. Proceedings of the 16th International Conference on Conceptual Structures (ICCS 2008), volume 5113 of Lecture Notes in Computer Science, page 133-146. Springer, (2008)
R. Thomopoulos, P. Buche, and O. Haemmerlé. Proceedings of the 11th International Conference on Conceptual Structures (ICCS 2003), volume 2746 of Lecture Notes in Computer Science, page 54-68. Springer, (2003)