R. Kumar, J. Novak, B. Pang, and A. Tomkins. Proceedings of the 16th international conference on World Wide Web, page 629--638. New York, NY, USA, ACM, (2007)
D. Beeferman, and A. Berger. KDD '00: Proceedings of the sixth ACM SIGKDD international conference on Knowledge discovery and data mining, page 407--416. New York, NY, USA, ACM, (2000)