U. Shardanand, and P. Maes. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 210--217. New York, NY, USA, ACM Press/Addison-Wesley Publishing Co., (1995)
I. Konstas, V. Stathopoulos, and J. Jose. Proceedings of the 32nd international ACM SIGIR conference on Research and development in information retrieval, page 195--202. New York, NY, USA, ACM, (2009)