1. a Austrian Research Institute for Artificial Intelligence , Schottengasse 3, Wien , 1010 , Austria
2. b Institut Gaspard Monge , Universite´ de Marne-la-Valle´e , Marne-la-Valle´e CEDEX 2 , 77454 , France
3. c Dept. Computer Science , King's College London , London , WC2R 2LS , England
4. d School of Computing , Curtin University of Technology , GPO Box 1987 U, WA
5. e LIFAR - ABISS , Universite´ de Rouen , Mont Saint Aignan, 76821, France
6. f School of Computing , Curtin University of Technology , GPO Box 1987 U, WA