F. Gey. Proceedings of the 17th annual international ACM SIGIR conference on Research and development in information retrieval, page 222--231. New York, NY, USA, Springer-Verlag New York, Inc., (1994)
J. Jiang, and C. Zhai. Proceedings of the 45th Annual Meeting of the Association of Computational Linguistics, page 264--271. Prague, Czech Republic, Association for Computational Linguistics, (June 2007)