Applied Computer Science, Faculty of Technology, Bielefeld University, Universitätsstrasse 25, D-33615 Bielefeld, Germany. marko@techfak.uni-bielefeld.de|Applied Computer Science, Faculty of Technology, Bielefeld University, Universitätsstrasse 25, D-33615 Bielefeld, Germany. marko@techfak.uni-bielefeld.de|Applied Computer Science, Faculty of Technology, Bielefeld University, Universitätsstrasse 25, D-33615 Bielefeld, Germany. marko@techfak.uni-bielefeld.de