1. Centre for Informatics and Systems of the University of Coimbra, Department of Informatics Engineering, University of Coimbra, Coimbra, Portugal & Karlsruhe Service Research Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany
2. Knowledge Media Institute, The Open University, Milton Keynes, England, UK
3. SAP Research, Karlsruhe, Germany
4. Centre for Informatics and Systems of the University of Coimbra Group, Department of Informatics Engineering, University of Coimbra, Coimbra, Portugal
5. Department of Computer Science, VU University Amsterdam, Amsterdam, The Netherlands