Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de|Institute of Computer Science, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany. grau@informatik.uni-halle.de