Interoperability between different rights expression languages and protection mechanisms

Interoperability is key for the real deployment of digital rights management (DRM) systems. 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 public specification that is being used by the Open Mobile Alliance (OMA), a relevant industrial forum in the area of mobile systems. In this paper, we have analysed a DRM specification from OMA, that uses ODRL, and we have tried to propose its implementation in an MPEG-21 environment. What we have found is that, on the one hand, we can simplify the use of MPEG-21 REL, and for this we define the corresponding subset for the REL schema and authorisation model, but, on the other hand, we need to extend the current MPEG-21 version to fulfil some OMA DRM features. Nevertheless, the use of Part 4 of MPEG-21 (IPMP, Intellectual Property Management and Protection) could solve some of the problems. All of these restrictions and extensions could be the starting point for a MPEG-21 profile for mobile applications. This approach could simplify the implementation of MPEG-21 REL applications.