D. Zhang, und W. Lee. WWW '04: Proceedings of the 13th international conference on World Wide Web, Seite 472--481. New York, NY, USA, ACM Press, (2004)
W. Lee. ICML '01: Proceedings of the Eighteenth International Conference on Machine Learning, Seite 314--321. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2001)