P. Schonhofen. WI '06: Proceedings of the 2006 IEEE/WIC/ACM International Conference on Web Intelligence, page 456--462. Washington, DC, USA, IEEE Computer Society, (2006)
L. Baker, and A. McCallum. Proceedings of SIGIR-98, 21st ACM International Conference on Research and Development in Information Retrieval, page 96--103. Melbourne, AU, ACM Press, New York, US, (1998)