Na Zhao Min Chen Shu-Ching Chen Mei-Ling Shyu MRBAC: Hierarchical Role Management and Security Access Control for Distributed Multimedia Systems. 76-82 2008 ISORC http://doi.ieeecomputersociety.org/10.1109/ISORC.2008.41 conf/isorc/2008 db/conf/isorc/isorc2008.html#ZhaoCCS08