R. Jäschke, F. Eisterlehner, A. Hotho, and G. Stumme. RecSys '09: Proceedings of the third ACM Conference on Recommender Systems, page 369--372. New York, NY, USA, ACM, (2009)
Y. Ahn, S. Han, H. Kwak, S. Moon, and H. Jeong. WWW '07: Proceedings of the 16th international conference on World Wide Web, page 835--844. New York, NY, USA, ACM, (2007)