C. Schmitz, A. Hotho, R. Jäschke, and G. Stumme. The Semantic Web: Research and Applications, volume 4011 of LNAI, page 530-544. Heidelberg, Springer, (2006)
P. Eklund, B. Groh, G. Stumme, and R. Wille. Conceptual Structures: Logical, Linguistic, and Computational, volume 1867 of LNAI, page 453-467. Heidelberg, Springer, (2000)
U. Brandes, and T. Willhalm. Proceedings of the symposium on Data Visualisation 2002, page 159--ff. Aire-la-Ville, Switzerland, Switzerland, Eurographics Association, (2002)