R. Jäschke, A. Hotho, C. Schmitz, and G. Stumme. Proc. 18. Workshop Grundlagen von Datenbanken, page 80-84. Halle-Wittenberg, Martin-Luther-Universität, (June 2006)
A. Mislove, B. Viswanath, K. Gummadi, and P. Druschel. Proceedings of the Third ACM International Conference on Web Search and Data Mining, page 251--260. New York, NY, USA, ACM, (2010)