L. Page, S. Brin, R. Motwani, and T. Winograd. Proceedings of the 7th International World Wide Web Conference, page 161--172. Brisbane, Australia, (1998)
I. Niles, and A. Pease. Proceedings of the 2nd International Conference on Formal Ontology in Information Systems (FOIS-2001), Ogunquit, Maine, (October 2001)