A. Sun, E. Lim, and W. Ng. Proceedings of the 4th international workshop on Web information and data management, page 96--99. New York, NY, USA, ACM, (2002)
D. Mladenic, and M. Grobelnik. ICML '99: Proceedings of the Sixteenth International Conference on Machine Learning, page 258--267. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (1999)