Q. He, B. Chen, J. Pei, B. Qiu, P. Mitra, and L. Giles. Proceedings of the 18th ACM conference on Information and knowledge management, page 957--966. New York, NY, USA, ACM, (2009)
J. Huang, Z. Zhuang, J. Li, and C. Giles. Proceedings of the 2008 International Conference on Web Search and Data Mining, page 107--116. New York, NY, USA, ACM, (2008)