F. Mitzlaff, M. Atzmueller, G. Stumme, and A. Hotho. Complex Networks IV, volume 476 of Studies in Computational Intelligence, Springer Verlag, Heidelberg, Germany, (2013)
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)