R. Jäschke, A. Hotho, C. Schmitz, B. Ganter, and G. Stumme. Proceedings of the 6th IEEE International Conference on Data Mining (ICDM 06), page 907-911. Hong Kong, IEEE Computer Society, (December 2006)
G. Stumme. Conceptual Structures: Knowledge Representation as Interlingua Proc. ICCS'96, volume 1115 of LNAI, page 308-320. Heidelberg, Springer, (1996)