Rights Expression Languages

Description

By G.R. Gangadharan and Michael Weiss, from the article, An Introduction to Rights Expression Languages:

"The foundation of DRM technology relies on our ability to represent the rights over digital assets. RELs represent the rights over assets in a machine-understandable way. RELs describe different aspects of usage control, payment, and access, for a digital access environment.

According to Parrott, a REL consists of four components:

• Subjects, the actors who perform some operation or action

• Objects, the content against which a subject wants to perform an

operation

• Operations or what the subjects wants to do to the object

• A set of constraints or conditions under which an operation can be

performed

These components and their relations support a range of models, each describing a way of applying digital rights. In general, a REL expresses the rights of an information asset either in some form of logic or in an XML-based language." (http://www.osbr.ca/archive.php#A4)

History

By G.R. Gangadharan and Michael Weiss

"What follows is a brief history of RELs. A pioneering formal language called DigitalRights describes a mathematical model of simple licenses that consists of payment and rendering events and a formal representation of licenses. LicenseScript is a logic-based REL.

Logic-based RELs express general prepositions of a permissive or obligatory (restrictive) statement. However, these languages cannot express a finer level of granularity of the assets, actors, or actions involved. Logic-based RELs cannot interoperate with other types of RELs.

XML-based RELs support interoperable ways of expressing the rights of an information asset. An XML-based REL allows asset producers to specify flexible expressions. The Extended Rights Markup Language (XrML) and the Open Digital Rights Language (ODRL) are two XML-based RELs which have gained international recognition and are widely used in industry.

XrML is the basis for the REL of the MPEG-21 multimedia framework. It focuses on the license through which a rights holder confers usage rights to a consumer. A license can be digitally signed by the rights holder, now also referred to as the issuer, to confirm that the holder grants the rights contained in the license. An XrML license contains one or multiple grants and the license issuer. A grant is the element within the license that authorizes a subject to exercise a right on some object under some constraints. Note that the actual terminology used by XrML is slightly different from this.

ODRL is an open standard language for the expression of terms and conditions over assets in open and trusted environments. ODRL consists of an expression language and a data dictionary. The expression language defines basic terms of rights expressions and their organization using a set of abstract concepts. The data dictionary defines the semantics of the concrete terms used to express an instance of a rights specification.

ODRL is based upon an extensible model for rights expression, and defines the following three core entities and their relationships:

• Assets, the objects being licensed

• Rights, the rules concerning permitted activities, the constraints

or limits to these permissions, the requirements or obligations needed to exercise the permission, and the conditions or specifications of exceptions that, if true, terminate the permissions and may require re-negotiation of the rights

• Parties, the information regarding the service provider, consumer,

or broker

With these entities, ODRL can express offers (proposals from rights holders for specific rights over their assets) and agreements (contracts or deals between the parties with specific offers). ODRL supports the declaration of a wide range of expressions. It can also be extended to different types of domains. For example, we can use ODRL to specify that a consumer of a geocoding web service can only use this service in a non-commercial context, as well as the number of times the service can be accessed each day. ODRL has been published by the World Wide Web Consortium (W3C), and has received wide acceptance. ODRL is supported by several industry consortia such as the Dublin Core Metadata Initiative (DCMI) and the Open Mobile Alliance (OMA).

Two applications of ODRL are an ODRL profile of the semantics of Creative Commons (CC) licenses and the ODRL profile for services (ODRL-S). The core semantics of CC licenses have been expressed in ODRL. This profile supports extensions to these semantics, and defines an XML Schema. ODRL-S is an extended version of ODRL to express clauses for service licensing, creating a machine-understandable service license." (http://www.osbr.ca/archive.php#A4)