Q. Zhao, S. Bhowmick, X. Zheng, and K. Yi. CIKM '08: Proceeding of the 17th ACM conference on Information and knowledge management, page 309--318. New York, NY, USA, ACM, (2008)
D. Auber, and F. Jourdan. IV '05: Proceedings of the Ninth International Conference on Information Visualisation, page 703--709. Washington, DC, USA, IEEE Computer Society, (2005)