1. Fraunhofer Institute for Software and Systems Engineering (ISST), Emil-Figge-Straße 91, 44227 Dortmund, Germany. meis@do.isst.fraunhofer.de
2. Fraunhofer Institute for Software and Systems Engineering (ISST), Emil-Figge-Straße 91, 44227 Dortmund, Germany. draeger@do.isst.fraunhofer.de