1. Lynch, C., Ashley, K.D., Pinkwart, N., Aleven, V.: Concepts, Structures, and Goals: Redefining Ill-Definedness. International Journal of AI in Education; Special Issue on Ill-Defined Domains 19(3), 253–266 (2009)
2. Lecture Notes in Computer Science;T. Dragon,2006
3. Lecture Notes in Computer Science;T. Dragon,2010
4. Lecture Notes in Computer Science;A. Rahati,2010
5. Lecture Notes in Computer Science;W. Chen,2010