T. Strohman, W. Croft, и D. Jensen. Proceedings of the 30th annual international ACM SIGIR conference on Research and development in information retrieval, стр. 705--706. New York, NY, USA, ACM, (2007)
Y. Zhou, и W. Croft. Proceedings of the 14th ACM International Conference on Information and Knowledge Management, стр. 331--332. New York, NY, USA, ACM, (2005)