M. Grahl, A. Hotho, and G. Stumme. Workshop Proceedings of Lernen - Wissensentdeckung - Adaptivität (LWA 2007), page 50-54. Martin-Luther-Universität Halle-Wittenberg, (September 2007)
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)