1. CITIC-Research Center of Information and Communication Technologies, University of A Coruña, A Coruña, Spain
2. Department of Computer Science and Information Technologies, Faculty of Communication Science, University of A Coruña, A Coruña, Spain
3. CISUC, Department of Informatics Engineering University of Coimbra, Coimbra, Portugal
4. Department of Computer Science and Information Technologies, Faculty of Computer Science, University of A Coruña, A Coruña, Spain