W. Cohen, und Y. Singer. 19th Annual International ACM SIGIR Conference on Research and Development in Information Retrieval, Seite 307--315. Zürich, CH, ACM Press, New York, US, (1996)
H. Ng, W. Goh, und K. Low. 20th Annual International ACM SIGIR Conference on Research and Development in Information Retrieval., Seite 67-73. New York, (1997)