A Rights Expression Language or REL is a machine-processable language used to express intellectual property rights (such as copyright) and other terms and conditions for use over content. RELs can be used as standalone expressions (i.e. metadata usable for search, compatibility tracking) or within a DRM system.
RELs are expressible in a machine-language (such as XML, RDF , RDF Schema, and JSON). Although RELs may be processed directly, they can also be encountered when embedded as metadata within other documents, such as eBooks, , or video files.
Notable RELs include:
: An RDF Schema used by the Creative Commons project to express their licences.
: This same vocabulary has also been adopted by the GNU Project to express their General Public License (GPL) in machine-readable form.
; W3C Open Digital Rights Language ODRL
: The W3C Permissions and Obligations Expression (POE) Working Group has developed the ODRL recommendations for expressing permiss