One of the key issues for the real deployment of Digital Rights Management (DRM) systems is interoperability. A clear example is at the level of Rights Expression Languages (RELs), where two of them are competing to have a place in the market. On the one hand, MPEG-21 REL is an ISO/IEC official standard, and on the other hand ODRL (Open Digital Rights Language) is a REL initiative that has been adopted by the Open Mobile Alliance (OMA), a relevant industrial forum in the area of mobile systems. MPEG-21 REL is more complete, but rather complex; this is why ODRL could be considered in some cases as a more flexible option.

In this paper, we analyse a DRM specification from OMA, and try to propose its implementation in an MPEG-21 environment. By defining an MPEG-21 REL DTD and a subset of the MPEG-21 REL Authorisation Model we are in fact specifying an MPEG-21 REL profile. This approach could simplify the implementation of MPEG-21 REL applications. In order to verify the feasibility of our proposal, we have also implemented some tools that work with both MPEG-21 REL and OMA DRM.