1. Institut National Polytechnique de Toulouse, 2, Rue Charles Camichel. BP 7122, 31071 Toulouse Cedex 7, France
2. University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
3. Institute for Systems and Computer Engineering, Technology and Science & University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal
4. Université Paul Sabatier, Toulouse III, 118, route de Narbonne, 31042 Toulouse Cedex, France
5. RWTH Aachen University, Germany & Universität Trier, FB IV - Computer Science, Human-Computer Interaction, Campus II - Building H - Room 441, Behringerstr. 21, 54296 Trier, Germany