R. Yates, and A. Tiberi. KDD '07: Proceedings of the 13th ACM SIGKDD international conference on Knowledge discovery and data mining, page 76--85. New York, NY, USA, ACM, (2007)
P. Brusilovsky. SOFSEM 2008: Theory and Practice of Computer Science, volume 4910 of Lecture Notes in Computer Science, chapter 2, Springer Berlin / Heidelberg, Berlin, Heidelberg, (2008)