In: Peter Brusilovsky; Albert T. Corbett; Fiorella De Rosis (Hrsg.). Proceedings of the 9th International Conference on User Modeling. International Conference on User Modeling (UM-2003), June 22-26, Johnstown, PA, USA, Pages 238-247, Lecture Notes in Computer Science (LNCS), Vol. 2702, ISBN 3-540-40381-7, Springer, Berlin, Heidelberg, 2003.