Center of Informatics, Federal University of Pernambuco, Recife, Brazil. igcf@cin.ufpe.br|Center of Informatics, Federal University of Pernambuco, Recife, Brazil. igcf@cin.ufpe.br|Center of Informatics, Federal University of Pernambuco, Recife, Brazil. igcf@cin.ufpe.br|Center of Informatics, Federal University of Pernambuco, Recife, Brazil. igcf@cin.ufpe.br