1. System Analysis and Modeling Group, Hasso Plattner Institute at the University Potsdam, Prof.-Dr.-Helmert-Strasse 2-3, D-14482 Potsdam, Germany
2. Software Engineering Group, University of Paderborn, Warburger Strasse 100, D-33098 Paderborn, Germany,
3. Software Engineering Group, University of Paderborn, Warburger Strasse 100, D-33098 Paderborn, Germany