R. Wille, and R. Wille-Henning. Proceedings of the 15th International Conference on Conceptual Structures (ICCS 2007), volume 4604 of Lecture Notes in Artificial Intelligence, page 269-282. Berlin, Heidelberg, Springer-Verlag, (July 2007)
P. Gehring, and R. Wille. Proceedings of the 14th International Conference on Conceptual Structures (ICCS 2006), volume 4068 of Lecture Notes in Computer Science, page 215-228. Springer, (2006)