Department of Computer, Control and Management, Engenerring Antonio Ruberti, Sapienza University of Rome, Via Ariosto 25, Rome, Italy;Department of Computer, Control and Management, Engenerring Antonio Ruberti, Center for the Evaluation of Language and Communication Technologies (CELCT), Via alla Casata 56/c, Povo, TN, Italy;Department of Computer Science, Database Group, University of Twente, Via alla Casata 56/c, Enschede, TN, The Netherlands;Department of Computer Science, Database Group, UNED Natural Language Processing and Information Retrieval Research Group, E.T.S.I. Informática de la UNED, c/ Juan del Rosal 16, Madrid, TN, S ...;Department of Computer, Control and Management, Engeneering Antonio Ruberti, Sapienza University of Rome, Via Ariosto 25, Rome, TN, Italy