A. Hotho, R. J�schke, C. Schmitz, and G. Stumme. The Semantic Web: Research and Applications, volume 4011 of Lecture Notes in Computer Science, page 411-426. Heidelberg, Springer, (June 2006)
E. Gabrilovich, S. Dumais, and E. Horvitz. WWW '04: Proceedings of the 13th international conference on World Wide Web, page 482--490. New York, NY, USA, ACM Press, (2004)