J. Vig, S. Sen, and J. Riedl. IUI '09: Proceedings of the 13th international conference on Intelligent user interfaces, page 47--56. New York, NY, USA, ACM, (2008)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. Proceedings of the Twenty-First International Joint Conference on Artificial Intelligence, page 2089-2094. Pasadena, California, USA, (2009)
R. Jäschke, A. Hotho, C. Schmitz, and G. Stumme. Proc. 18. Workshop Grundlagen von Datenbanken, page 80-84. Halle-Wittenberg, Martin-Luther-Universität, (June 2006)