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)
S. Krolak-Schwerdt, P. Orlik, and B. Ganter. Studies in Classification, Data Analysis, and Knowledge Organization, volume 4 of Information systems and data analysis, Springer, Berlin, (1994)