user- Proceedings of the 9th International Conference of the Learning Sciences - Volume 1, page 9--16. International Society of the Learning Sciences, (2010)
- Knowledge Management Research \&\#38; Practice 8(1):33--44 (2010)
- Journal of Computer Assisted Learning 25(6):549--561 (2009)
- Motivation, emotion, and cognition: integrative perspectives on intellectual functioning and development, Lawrence Erlbaum, Mahwah, NJ, (2004)
- User Model. User-Adapt. Interact. 4(4):253-278 (1995)
- Intelligent Tutoring Systems, volume 5091 of Lecture Notes in Computer Science, page 406-415. Springer, (2008)
- Computers in Human Behavior 25(2):360--370 (2009)
- Interacting with Computers 12(4):409-426 (2000)
- Instructional Science 14(3):293--326 (May 1986)
- Computers & Education 54(4):932-940 (2009)
- RWTH Aachen, Aachen, (2009), ISSN 1613-0073 .
- Adaptive evolutionary information systems, Idea Group, Hershey, (2002)
- Theoretical foundations of learning environments, Routledge, New York, (2000)
- Instructional-design theories and models: a new paradigm of instructional theory, Lawrence Erlbaum Associates, Mahwah, New Jersey, 2nd edition edition, (1999)
- Educational Technology Research and Development 53(3):83--93 (2005)
- Educational Measurement: Issues and Practice 25(4):6-20 (2006)
- Knowledge Spaces: Theories, Empirical Research, Applications, Lawrence Erlbaum Associates, Mahwah, NJ, (1999)
- International Journal on E Learning 5(1):75-88 (2006)
- Artificial Intelligence 42(1):7-49 (1990)
- WWW Alt. '04: Proceedings of the 13th international World Wide Web conference on Alternate track papers \& posters, page 104--113. New York, NY, USA, ACM Press, (2004)
