S. Jespersen, T. Pedersen, and J. Thorhauge. Proceedings of the 5th ACM International Workshop on Web Information and Data Management, page 82--89. New York, NY, USA, ACM, (2003)
X. Wu, L. Zhang, and Y. Yu. WWW '06: Proceedings of the 15th international conference on World Wide Web, page 417--426. New York, NY, USA, ACM Press, (2006)