1. Universtity of Coimbra,CISUC & Dep. of Informatics Engineering,Coimbra,Portugal
2. University of Porto,LIACC &, Faculty of Engineering,Porto,Portugal
3. University of Lisbon,Dep. of Informatics,Lisbon,Portugal
4. University of Porto,Faculty of Engineering,LIACC & Dep. of Informatics Engineering,Porto,Portugal