Rui Silva
1) Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Porto, Portugal. 2) Universidade de Trás-os-Montes e Alto Douro,
Portugal

Henrique S. Mamede
1) Institute for Systems and Computer Engineering, Technology and Science (INESC TEC), Porto, Portugal. 3) Department of Science and Technology, Universidade Aberta, Lisbon,
Portugal

Vitor Santos
NOVA Information Management School, Universidade Nova de Lisboa, Lisbon,
Portugal