F. Liu, C. Yu, and W. Meng. Proceedings of the Eleventh International Conference on Information and Knowledge Management, page 558--565. New York, NY, USA, ACM, (2002)
X. Shen, B. Tan, and C. Zhai. Proceedings of the 14th ACM International Conference on Information and Knowledge Management, page 824--831. New York, NY, USA, ACM, (2005)