Department of Computer Science, University of Illinois at Chicago, 851 South Morgan Street (M/C 152), Chicago, IL;Digital Enterprise Research Institute, National University of Ireland, Galway, IDA Business Park, Lower Dangan, 851 South Morgan Street (M/C 152), Galway, IL, Ireland;Digital Enterprise Research Institute, TopQuadrant, 851 South Morgan Street (M/C 152), Galway, VA, Ireland;Digital Enterprise Research Institute, HP Laboratories, 851 South Morgan Street (M/C 152), Bristol, VA, UK;Departamento de Informática - Pontifícia, Universidade Católica do Rio de Janeiro,, (PUC Rio) - Caixa Postal 38.097, Rio de Janeiro, RJ, Brazil