X. Liu, and W. Croft. Proceedings of the 27th Annual International ACM SIGIR Conference on Research and Development in Information Retrieval, page 186--193. New York, NY, USA, ACM, (2004)
Q. Miao, Q. Li, and R. Dai. Proceeding of the 17th ACM conference on Information and knowledge management, page 1369--1370. New York, NY, USA, ACM, (2008)
C. Brooks, and N. Montanez. WWW '06: Proceedings of the 15th international conference on World Wide Web, page 625--632. New York, NY, USA, ACM Press, (2006)