R. Kent. Proceedings of the 17th International Conference on Conceptual Structures (ICCS 2009), volume 5662 of Lecture Notes in Computer Science, page 201-218. Springer, (2009)
A. Torim, and K. Lindroos. Proceedings of the 16th International Conference on Conceptual Structures (ICCS 2008), volume 5113 of Lecture Notes in Computer Science, page 175-188. Springer, (2008)