J. Lafferty, A. McCallum, und F. Pereira. Proceedings of the Eighteenth International Conference on Machine Learning, Seite 282--289. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2001)
L. Baker, und A. McCallum. Proceedings of SIGIR-98, 21st ACM International Conference on Research and Development in Information Retrieval, Seite 96--103. Melbourne, AU, ACM Press, New York, US, (1998)