Center of Informatics, Federal University of Pernambuco, Recife 50740-560, Brazil.|Center of Informatics, Federal University of Pernambuco, Recife 50740-560, Brazil.|Center of Informatics, Federal University of Pernambuco, Recife 50740-560, Brazil.|Center of Informatics, Federal University of Pernambuco, Recife 50740-560, Brazil.