Michael Hafner Mukhtiar Memon Muhammad Alam Modeling and Enforcing Advanced Access Control Policies in Healthcare Systems with Sectet. 132-144 2007 MoDELS Workshops http://dx.doi.org/10.1007/978-3-540-69073-3_15 conf/models/2007w db/conf/models/models2007w.html#HafnerMA07