G. Geleijnse, and J. Korst. Proceedings Third Philips Symposium on Intelligent Algorithms (SOIA 2006), page 171 -- 182. Eindhoven, the Netherlands, (December 2006)
P. Chirita, S. Costache, W. Nejdl, and S. Handschuh. Proceedings of the 16th International World Wide Web Conference,
WWW 2007, Banff, Canada, page 845--854. New York, NY, USA, ACM Press, (2007)