L. Wu, L. Yang, N. Yu, and X. Hua. WWW '09: Proceedings of the 18th international conference on World wide web, page 361--370. New York, NY, USA, ACM, (2009)
J. Lin, C. Yang, S. Tseng, and C. Huang. Language, Information, and Computation - Proceedings of the 16th Pacific Asia Conference, page 320--329. (February 2002)