1. R&D Engineer, Institute of Computer Science, Foundation of Research and Technology–Hellas (FORTH), Vassilika Vouton, P.O. Box 1385, GR-711-10, Heraklion, Crete, Greece.
2. Associate Researcher, Institute of Computer Science, Foundation of Research and Technology–Hellas (FORTH), Vassilika Vouton, P.O. Box 1385, GR-711-10, Heraklion, Crete, Greece.
3. Visiting Researcher, Institute of Computer Science, Foundation of Research and Technology–Hellas (FORTH), 65 Ag. Ioannou, Athens 15341, Greece (corresponding author). E-mail: yste@ath.forthnet.gr