X. Wen, Y. Lin, C. Trattner, and D. Parra. Proceedings of the 25th ACM Conference on Hypertext and Social Media, page 285--290. New York, NY, USA, ACM, (2014)
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)