M. Sahami, S. Dumais, D. Heckerman, and E. Horvitz. Learning for Text Categorization: Papers from the 1998 Workshop, Madison, Wisconsin, AAAI Technical Report WS-98-05, (1998)
D. Koller, and M. Sahami. Proceedings of the 14th International Conference on Machine Learning (ML), Nashville, Tennessee,July 1997, page 170--178. (1997)