M. Chi, P. Jordan, K. VanLehn, and D. Litman. Proceeding of the 2009 conference on Artificial Intelligence in Education: Building Learning Systems that Care: From Knowledge Representation to Affective Modelling, page 197--204. Amsterdam, The Netherlands, The Netherlands, IOS Press, (2009)
K. Forbes-Riley, and D. Litman. Proceedings of the main conference on Human Language Technology Conference of the North American Chapter of the Association of Computational Linguistics, page 264--271. Stroudsburg, PA, USA, Association for Computational Linguistics, (2006)