1. Department of Computer Science Engineering, Instituto Superior Tecnico, Lisbon, Portugal
2. INESC TEC–Institute for Systems and Computer Engineering, Technology and Science, Porto, Portugal
3. Department of Sciences and Technology, Universidade Aberta, Rua da Escola Politécnica, Lisboa, Portugal
4. Department of Computer Science, ISCTE-UIL–Instituto Universitário de Lisboa, Lisbon, Portugal