Center for Applied Computer Science, University of Cologne Weyertal 80, 50931 Cologne, Germany. {radde.gebert}@zpr.uni-koeln.de|Center for Applied Computer Science, University of Cologne Weyertal 80, 50931 Cologne, Germany. {radde.gebert}@zpr.uni-koeln.de|Center for Applied Computer Science, University of Cologne Weyertal 80, 50931 Cologne, Germany. {radde.gebert}@zpr.uni-koeln.de