M. McLaughlin, and J. Herlocker. SIGIR '04: Proceedings of the 27th annual international ACM SIGIR conference on Research and development in information retrieval, page 329--336. New York, NY, USA, ACM Press, (2004)
C. Nodder, G. Williams, and D. Dubrow. GROUP '99: Proceedings of the international ACM SIGGROUP conference on Supporting group work, page 150-159. New York, NY, USA, ACM Press, (1999)