G. Reif, H. Gall, and M. Jazayeri. WWW '05: Proceedings of the 14th international conference on World Wide Web, page 722--729. New York, NY, USA, ACM Press, (2005)
T. Gruber, and G. Olsen. Proceedings of the 4th International Conference on Principles of Knowledge Representation and Reasoning (KR'94). Bonn, Germany, May 24-27, 1994., page 258-269. Morgan Kaufmann, (1994)