Rafae Bhatti Daniel Sanz Elisa Bertino Arif Ghafoor A Policy-Based Authorization Framework for Web Services: Integrating XGTRBAC and WS-Policy. 447-454 2007 conf/icws/2007 ICWS http://doi.ieeecomputersociety.org/10.1109/ICWS.2007.10 db/conf/icws/icws2007.html#BhattiSBG07