R. Wetzker, C. Zimmermann, C. Bauckhage, and S. Albayrak. Proceedings of the third ACM international conference on Web search and data mining, page 71--80. New York, NY, USA, ACM, (2010)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)