About ISO/IEC 21000-6, the MPEG-21 Rights Data Dictionary

The ISO MPEG Rights Data Dictionary (RDD) provides the basis for a resource to create widely understood, consistent meaning for Digital Rights Management (DRM) systems. The RDD is available to all those involved in building and deploying DRM systems to ensure that the terms used in permissions granted by the systems can be interpreted consistently.

The RDD specification is intended to support the ISO MPEG Rights Expression Language (and other systems requiring semantic interoperability). Together, the two standards provide interoperable ways of expressing rules and interoperable ways of communicating the meaning of these rules. This is to the benefit of rights holders, who can be confident that business rules can be interpreted consistently and to consumers, who can be sure that usage permissions will not vary unpredictably across different systems. Manufacturers can also benefit because their systems can interoperate without detailed negotiation on the interpretation of permissions. The Registration Authority enables rights management systems, device manufacturers and

other parties to register their terms in a database, which will provide the basis for automated queries to determine the precise meaning of terms in permissions. By providing a set of standard meanings to enable different communities to exchange precise information, the system cuts down on possible misinterpretation. Rights are complex and many metadata schemes are already in use; the deployment of an interoperable and standard dictionary provides a solution to cope with this real-world diversity. The MPEG RDD is a realisation of the concept of semantic interoperability.

The text of ISO/IEC 21000-6 can be obtained from ISO or from a local national standards organisation.


The MPEG-21 Rights Data Dictionary (RDD) comprises a set of clear, consistent, structured, integrated and uniquely identified terms to support the MPEG-21 Rights Expression Language (REL) as specified in ISO/IEC 21000-5. A methodology and structure for the Dictionary is also standardised, along with the method by which further Terms can be added to the Dictionary through a Registration Authority. The methodology is based on a contextual ontology architecture, and was developed from earlier work on interoperability of data in e-commerce systems (indecs).

The RDD is a prescriptive Dictionary, in the sense that it defines a single meaning for a Term, but it is also inclusive in that it can recognise and incorporate terms and definitions governed by organisations other than MPEG. These terms can be incorporated through mapping into the standard ontology. The standard specifies an audit process so that additions, amendments and deletions to terms and their attributes can be tracked.

MPEG-21 RDD recognises legal definitions only as terms from other organisations that can be mapped into the RDD Dictionary through the Registration Authority. Terms that are directly authorised by the RDD Registration Authority neither define nor prescribe intellectual property rights or other legal entities.

Relationship of ISO/IEC 21000-6 to existing Metadata Schemes

As noted above, as well as providing terms for the REL, the RDD is designed to support the mapping of terms from different namespaces. The purpose of such mapping is to enable the transformation of metadata from the terminology of one namespace into that of another namespace. This will facilitate the communication of meaning between communities having different metadata schemes. The mapping process, specified to ensure minimum ambiguity or loss of semantic integrity, will be the responsibility of the Registration Authority, which is required by the standard to provide term look-up.

Relationship of ISO/IEC 21000-6 to other activities

The ISO/IEC 21000-6 dictionary was designed as a component of MPEG-21to support the MPEG REL (Rights Expression Language). However it embodies many useful generic concepts such as relators for typed links between identifiers. While it will clearly not be a single resource for all content interoperability mappings, nor take advantage of all potential ontology tools, nonetheless as the first public, and standard, implementation of the underlying methodology of semantic interoperability mapping through a contextual ontology there is great potential for use elsewhere, creating both economies of scale and critical mass of support.

The most effective route to ensure such critical mass would be to promote the adoption of ISO/IEC 21000-6 as a solution for other initiatives which encounter the same problem of semantic interoperability, where this meets the needs. The Registration Authority, with its Registration Authority Management Group and associates including CONTECS (a consortium formed in 2001 to work on tools for the sharing of understanding of the meaning in rights management systems) is promoting the adoption of ISO/IEC 21000-6 in other sectors and initiatives where similar requirements have been identified.

Methodology of ISO/IEC 21000-6

The RDD is a structured ontology, in which meaning, once it has been defined, can be passed on from one term to another by logical rules of association such as inheritance and opposition. In recognition of the great diversity and complexity associated with multimedia content, it is designed to represent as many different specialisations of meaning as its users require, and to show their relationships in a structured way in order to support the mapping and transformation of terms between different schemas and systems.

Terms in ISO/IEC 21000-6

The MPEG-21 RDD currently contains about 2000 standardised terms. The majority of these are necessary for the structure of the RDD and for enabling extensibility of the Dictionary. Other terms are directly related to the use creation of REL permissions and the expression of rights ownership.

Included in these terms are the following fourteen rights:

These terms are basic and can be specialised for more complex operations on rights protected content. A description of this specialisation process is also contained in the standard.

This specialization is performed through registering the terms through the ISO/IEC 21000-6 Registration Authority.