S. Doerfel, R. Jäschke, A. Hotho, and G. Stumme. Proceedings of the 4th ACM RecSys workshop on Recommender systems and the social web, page 9--16. New York, NY, USA, ACM, (September 2012)
R. Jäschke, A. Hotho, F. Mitzlaff, and G. Stumme. Recommender Systems for the Social Web, volume 32 of Intelligent Systems Reference Library, Springer, Berlin/Heidelberg, (2012)