LaSIGE, Faculty of Sciences, University of Lisboa, Lisboa, Portugal. cpesquita@xldb.di.fc.ul.pt|LaSIGE, Faculty of Sciences, University of Lisboa, Lisboa, Portugal. cpesquita@xldb.di.fc.ul.pt|LaSIGE, Faculty of Sciences, University of Lisboa, Lisboa, Portugal. cpesquita@xldb.di.fc.ul.pt|LaSIGE, Faculty of Sciences, University of Lisboa, Lisboa, Portugal. cpesquita@xldb.di.fc.ul.pt|LaSIGE, Faculty of Sciences, University of Lisboa, Lisboa, Portugal. cpesquita@xldb.di.fc.ul.pt