C. Lu, X. Chen, and E. Park. CIKM '09: Proceeding of the 18th ACM conference on Information and knowledge management, page 1545--1548. New York, NY, USA, ACM, (2009)
A. Popescul, L. Ungar, D. Pennock, and S. Lawrence. Proceedings of the 17th Conference on Uncertainty in Artificial Intelligence, page 437--444. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (August 2001)