P. Brusilovsky, and E. Millán. chapter User models for adaptive hypermedia and adaptive educational systems, Springer-Verlag, Berlin, Heidelberg, (2007)
S. Lindstaedt, G. Beham, B. Kump, and T. Ley. Learning in the Synergy of Multiple Disciplines, Proceedings of the EC-TEL 2009, volume 5794 of Lecture Notes in Computer Science, Berlin/Heidelberg, Springer, (October 2009)