Z. Guo, Z. Xu, S. Zhou, A. Zhou, and M. Li. Conceptual Modeling for Novel Application Domains, ER 2003 Workshop Proceedings, volume 2814 of Lecture Notes in Computer Science, page 261-272. Chicago, Illinois, Springer-Verlag, (October 2003)
D. Bryant, J. Tsang, P. Kearney, and M. Li. Proceedings of the Eleventh Annual ACM-SIAM Symposium on Discrete Algorithms (San Francisco, CA, 2000), page 285--286. New York, ACM, (2000)