M. Halvey, and M. Keane. WWW '07: Proceedings of the 16th international conference on World Wide Web, page 1313--1314. New York, NY, USA, ACM Press, (2007)
D. Zhou, J. Bian, S. Zheng, H. Zha, and C. Giles. WWW '08: Proceeding of the 17th international conference on World Wide Web, page 715--724. New York, NY, USA, ACM, (2008)