D. Millen, J. Feinberg, and B. Kerr. CHI '06: Proceedings of the SIGCHI conference on Human Factors in computing systems, page 111--120. New York, NY, USA, ACM Press, (2006)
M. Grahl, A. Hotho, and G. Stumme. 7th International Conference on Knowledge Management (I-KNOW '07), page 356-364. Graz, Austria, Know-Center, (September 2007)