M. Grahl, A. Hotho, and G. Stumme. Workshop Proceedings of Lernen - Wissensentdeckung - Adaptivität (LWA 2007), page 50-54. Martin-Luther-Universität Halle-Wittenberg, (September 2007)
L. Zhao, and M. Zaki. SIGMOD '05: Proceedings of the 2005 ACM SIGMOD international conference on Management of data, page 694--705. New York, NY, USA, ACM, (2005)