K. Tu, J. Lu, H. Zhu, G. Liu, and Y. Yu. Proceedings of the 11th International Conference on Conceptual Structures (ICCS 2003), volume 2746 of Lecture Notes in Computer Science, page 378-391. Springer, (2003)
J. Zhong, H. Zhu, J. Li, and Y. Yu. Proceedings of the 10th International Conference on Conceptual Structures (ICCS 2002), volume 2393 of Lecture Notes in Computer Science, page 92-196. Springer, (2002)