F. Radlinski, and T. Joachims. KDD '05: Proceeding of the eleventh ACM SIGKDD international conference on Knowledge discovery in data mining, page 239--248. New York, NY, USA, ACM Press, (2005)
Z. Cao, T. Qin, T. Liu, M. Tsai, and H. Li. ICML '07: Proceedings of the 24th international conference on Machine learning, page 129--136. New York, NY, USA, ACM, (2007)