I. Ruthven. SIGIR '03: Proceedings of the 26th annual international ACM SIGIR conference on Research and development in informaion retrieval, page 213--220. New York, NY, USA, ACM Press, (2003)
C. Buckley, G. Salton, and J. Allan. SIGIR '94: Proceedings of the 17th annual international ACM SIGIR conference on Research and development in information retrieval, page 292--300. New York, NY, USA, Springer-Verlag New York, Inc., (1994)