M. Hu, E. Lim, A. Sun, H. Lauw, and B. Vuong. Proceedings of the Sixteenth ACM Conference on Conference on Information and Knowledge Management, page 243--252. New York, NY, USA, ACM, (2007)
T. Hu, H. Xiong, W. Zhou, S. Sung, and H. Luo. SIGIR '08: Proceedings of the 31st annual international ACM SIGIR conference on Research and development in information retrieval, page 871--872. New York, NY, USA, ACM, (2008)