Prathima Rao Gabriel Ghinita Elisa Bertino Jorge Lobo Visualization for Access Control Policy Analysis Results Using Multi-level Grids. 25-28 2009 POLICY http://doi.ieeecomputersociety.org/10.1109/POLICY.2009.29 conf/policy/2009 db/conf/policy/policy2009.html#RaoGBL09