M. Carman, M. Baillie, R. Gwadera, and F. Crestani. SIGIR '09: Proceedings of the 32nd international ACM SIGIR conference on Research and development in information retrieval, page 123--130. New York, NY, USA, ACM, (2009)
B. Liu, R. Jones, and K. Klinkner. CIKM '06: Proceedings of the 15th ACM international conference on Information and knowledge management, page 836--837. New York, NY, USA, ACM Press, (2006)
U. Lee, Z. Liu, and J. Cho. WWW '05: Proceedings of the 14th international conference on World Wide Web, page 391--400. New York, NY, USA, ACM Press, (2005)