Z. Zheng, K. Chen, G. Sun, and H. Zha. SIGIR '07: Proceedings of the 30th annual international ACM SIGIR conference on Research and development in information retrieval, page 287--294. New York, NY, USA, ACM Press, (2007)
J. Sun, H. Zeng, H. Liu, Y. Lu, and Z. Chen. WWW '05: Proceedings of the 14th international conference on World Wide Web, page 382--390. New York, NY, USA, ACM Press, (May 2005)