C. Lu, X. Chen, und E. Park. Proceeding of the 18th ACM conference on Information and knowledge management, Seite 1545--1548. New York, NY, USA, ACM, (2009)
D. Lawrie, und W. Croft. Proceedings of the 26th Annual International ACM SIGIR Conference on Research and Development in Information Retrieval, SIGIR 2003, Seite 457--458. (2003)