A. Hotho, R. Jäschke, C. Schmitz, and G. Stumme. Proceedings of the Conceptual Structures Tool Interoperability Workshop at the 14th International Conference on Conceptual Structures, page 87-102. Aalborg University Press, (February 2006)
C. Zahn. SIGCSE '87: Proceedings of the eighteenth SIGCSE technical symposium on Computer science education, page 264--266. New York, NY, USA, ACM, (1987)