Improvement of MPEG-21 right expression language

Digital Rights Management (DRM) allows controlling the access, the use and the diffusion of digital contents produced by right holders. A rights expression language (REL) is necessary. In order to guarantee these rights, the MPEG-21 REL was proposed which is a standardized language used to express the licenses. In this paper, we propose a new MPEG-21 REL model with a formal description and license interpretation process. By introducing the role concept we improve the MPEG 21 REL expressivity. This will be illustrated by several examples.