G. Xue, H. Zeng, Z. Chen, W. Ma, H. Zhang, and C. Lu. SIGIR '03: Proceedings of the 26th annual international ACM SIGIR conference on Research and development in informaion retrieval, page 56--63. New York, NY, USA, ACM, (2003)
J. Zhou, C. Ding, and D. Androutsos. CASCON '06: Proceedings of the 2006 conference of the Center for Advanced Studies on Collaborative research, New York, NY, USA, ACM, (2006)
Gabriel, J. Yu, H. Liu, and P. Yu. KDD '07: Proceedings of the 13th ACM SIGKDD international conference on Knowledge discovery and data mining, page 300--309. New York, NY, USA, ACM, (2007)