M. Becker, J. Mueller, A. Hotho, and G. Stumme. Conference on Pervasive and Ubiquitous Computing Adjunct Publication, page 1175--1182. New York, NY, USA, (2013)
R. J�schke, A. Hotho, C. Schmitz, and G. Stumme. Proc. 18. Workshop Grundlagen von Datenbanken, page 80-84. Halle-Wittenberg, Martin-Luther-Universit�t, (June 2006)