W. Xi, B. Zhang, Z. Chen, Y. Lu, S. Yan, W. Ma, and E. Fox. WWW '04: Proceedings of the 13th international conference on World Wide Web, page 319--327. New York, NY, USA, ACM Press, (2004)
W. Xi, E. Fox, W. Fan, B. Zhang, Z. Chen, J. Yan, and D. Zhuang. SIGIR '05: Proceedings of the 28th annual international ACM SIGIR conference on Research and development in information retrieval, page 130--137. New York, NY, USA, ACM, (2005)