3[2]Llorente S,Rodriguez E,Delgado J.Workflow description of digital rights management systems[R].Larnaca Cyprus:International Federated Conferences,2004.
4[4]MPEG-21,Part 5:Rights Expression Language (REL)[EB/OL].(2000-11-08)[2001-02-18].http://www.chiariglione.org/mpeg/standards/mpeg-21/mpeg-21.htm.
5[5]RightsCom ltd.The MPEG-21 Rights Expression Language-A White Paper[M].Philadephia:Saunders,2003.
6[6]ContentGuard Inc.Profiling MPEG Rights Expression Language:Concept,Approach and Applications[M].Geneva:Saunders,2003.
7Marc A. Kaplan, IBM Crytolope. Super Distribution and Digital Rights Management [EB/OL]. http://www.research.ibm. com/people/k/kaplank,2005 - 04 - 18.