Department of Computer and Information Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. sandve@ntnu.no|Department of Computer and Information Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. sandve@ntnu.no|Department of Computer and Information Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. sandve@ntnu.no|Department of Computer and Information Science, Norwegian University of Science and Technology (NTNU), Trondheim, Norway. sandve@ntnu.no