J. Freyne, S. Anand, I. Guy, and A. Hotho. Proceedings of the fifth ACM conference on Recommender systems, page 383--384. New York, NY, USA, ACM, (2011)
B. Bullock, H. Lerch, A. Roßnagel, A. Hotho, and G. Stumme. Proceedings of the 11th International Conference on Knowledge Management and Knowledge Technologies, page 15:1--15:8. New York, NY, USA, ACM, (2011)