K. Schoefegger, P. Seitlinger, and T. Ley. Proceedings of the 1st Workshop on Recommender Systems for Technology Enhanced Learning (RecSysTEL 2010), 1, page 2829 - 2838. (Sep 7, 2010)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)