C. Buckley, and G. Salton. SIGIR '95: Proceedings of the 18th annual international ACM SIGIR conference on Research and development in information retrieval, page 351--357. New York, NY, USA, ACM Press, (1995)
A. Singhal, M. Mitra, and C. Buckley. Proceedings of SIGIR-97, 20th ACM International Conference on Research and Development in Information Retrieval, page 25--32. Philadelphia, US, (1997)