D. Calvanese, T. Eiter, and M. Ortiz. Proceedings of the 21st International Joint Conference on Artificial Intelligence. AAAI Press/IJCAI, 2009., (July 2009)
M. Ortiz, and D. Calvanese. Proceedings of the 21st International Joint Conference on Artificial Intelligence. AAAI Press/IJCAI, 2009., (July 2009)To appear.