1. Parallel Systems, Department of Computing Science, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany. eike.best@informatik.uni-oldenburg.de
2. Département d’Informatique, Université Libre de Bruxelles, Boulevard du Triomphe, C.P. 212, B-1050 Bruxelles, Belgium, rdevil@ulb.ac.be
3. Parallel Systems, Department of Computing Science, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany. evgeny.erofeev@informatik.uni-oldenburg.de
4. Parallel Systems, Department of Computing Science, Carl von Ossietzky Universität Oldenburg, D-26111 Oldenburg, Germany. harro.wimmel@informatik.uni-oldenburg.de