Department of Computer Science, University of Leipzig, Leipzig, Germany. berni@tbi.univie.ac.at|Department of Computer Science, University of Leipzig, Leipzig, Germany. berni@tbi.univie.ac.at|Department of Computer Science, University of Leipzig, Leipzig, Germany. berni@tbi.univie.ac.at|Department of Computer Science, University of Leipzig, Leipzig, Germany. berni@tbi.univie.ac.at|Department of Computer Science, University of Leipzig, Leipzig, Germany. berni@tbi.univie.ac.at