R. Dieng, and S. Hug. Conceptual Structures: Therory, Tools and Applications, Proceedings of the 6th International Conference on Conceptual Structures (ICCS-1998), volume 1453 of LNAI, Montpellier (France), Sprineger-Verlag, (1998)
H. Chalupsky. Proceedings of the 7th International Conference on Principles of Knowledge Representation and Reasoning (KR-2000), page 471--482. Breckenridge (USA), Morgan Kaufmann Publishers, (2000)