Rights Expression Language
Encyclopedia
A Rights Expression Language or REL is a machine-processable language used for Digital Rights Management
.
Most REL are expressible in XML
, but this is not a requirement and any format could be used.XrML began in Lisp. Some use RDF
and RDF Schema
. Although RELs may be processed directly, they will most commonly be encountered when embedded as metadata
within other documents, such as eBooks, MP3
audio or downloaded video.
ccREL
ODRL
XrML
Digital rights management
Digital rights management is a class of access control technologies that are used by hardware manufacturers, publishers, copyright holders and individuals with the intent to limit the use of digital content and devices after sale. DRM is any technology that inhibits uses of digital content that...
.
Most REL are expressible in XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
, but this is not a requirement and any format could be used.XrML began in Lisp. Some use RDF
Resource Description Framework
The Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
and RDF Schema
RDF Schema
RDF Schema is a set of classes with certain properties using the RDF extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called RDF vocabularies, intended to structure RDF resources...
. Although RELs may be processed directly, they will most commonly be encountered when embedded as metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
within other documents, such as eBooks, MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
audio or downloaded video.
Notable RELs
Notable RELs include:ccREL
- An RDF SchemaRDF SchemaRDF Schema is a set of classes with certain properties using the RDF extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called RDF vocabularies, intended to structure RDF resources...
used by the Creative CommonsCreative CommonsCreative Commons is a non-profit organization headquartered in Mountain View, California, United States devoted to expanding the range of creative works available for others to build upon legally and to share. The organization has released several copyright-licenses known as Creative Commons...
project to express their licencesCreative Commons licensesCreative Commons licenses are several copyright licenses that allow the distribution of copyrighted works. The licenses differ by several combinations that condition the terms of distribution. They were initially released on December 16, 2002 by Creative Commons, a U.S...
. - This same vocabulary has also been adopted by the GNU ProjectGNU ProjectThe GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984...
to express their General Public License (GPL)GNU General Public LicenseThe GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....
in machine-readable form.
ODRL
ODRL
ODRL is an XML-based standard Rights Expression Language used in Digital Rights Management systems and open content management systems. ODRL is managed by an open organization that's open to public participation...
- An open standard for an XML-based REL.
XrML
XrML
XrML is the eXtensible Rights Markup Language which has also been standardized as the Rights Expression Language for MPEG-21. XrML is owned by ContentGuard....
- XrML began with work at Xerox in the 1990s.XrML.org After passing through several versions and separate projects, it later formed the basis of the REL for MPEG-21.
MPEG-21MPEG-21The MPEG-21 standard, from the Moving Picture Experts Group, aims at defining an open framework for multimedia applications. MPEG-21 is ratified in the standards ISO/IEC 21000 - Multimedia framework .MPEG-21 is based on two essential concepts:...
- Part 5 of this MPEGMoving Picture Experts GroupThe Moving Picture Experts Group is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression and transmission. It was established in 1988 by the initiative of Hiroshi Yasuda and Leonardo Chiariglione, who has been from the beginning the Chairman...
standard includes a REL.
METSRights- METSRights is an extension schema to the METSMETSThe Metadata Encoding and Transmission Standard is a metadata standard for encoding descriptive, administrative, and structural metadata regarding objects within a digital library, expressed using the XML schema language of the World Wide Web Consortium...
packaging metadata standard.
Use of a REL
The function of a REL is to define licences, and to describe these licences in terms of the permissions or restrictions they imply for how the related content may then be used.
"Licence" here may mean either:- A "well-known licence", such as GFDL, Apache LicenseApache LicenseThe Apache License is a copyfree free software license authored by the Apache Software Foundation . The Apache License requires preservation of the copyright notice and disclaimer....
or a Creative CommonsCreative CommonsCreative Commons is a non-profit organization headquartered in Mountain View, California, United States devoted to expanding the range of creative works available for others to build upon legally and to share. The organization has released several copyright-licenses known as Creative Commons...
CC-by-sa-3.0 etc. - A pre-defined licence that is like these, but not so well-known. Examples would be proprietary "shrinkwrap" licences.
- A specific licence that is created afresh, for one piece of content licensed to one user.
Well-known licences
Use of a well-known licence is often chosen for its unambiguous simplicity: GFDL means the same no matter who is using it. It is also practical to use such a licence, and to check that a project is complying with it, without understanding too much about what detail it entails. Merely knowing that "GFDL is acceptable to this project" and "All resources within this project use GFDL" is sufficient. In that sense, well-known licences are a way to avoid needing to use a REL to model the details of a licence, its name alone is enough.
Despite this, a REL may still be useful with these licences. It provides a machine-processable way to identify the licence in use, avoiding naming issues and potential ambiguities between "Apache License" or "Apache 2.0 Licence". The authors of these licences also require a means to describe their internal details.
Pre-defined licence
These are similar to the well-known licences, in that they're defined before their use and can be applied to many instances of licensing. Their difference is that as they're not well known, it's also necessary to explain what each of them entails, as the user is always likely to be encountering each of them for the first time. A REL provides the means to do this.
Using licensed content within a project now requires evaluation of the statement, "Are there any resources within this project whose licence forbids a condition that the project requires, or requires a condition that the project cannot permit?". These might include a necessary ability to distribute copies of the project afterwards, or a condition for accreditation on a splash screen that might be unacceptable to some projects.
In open source software development, it's also common for projects to create their own licence under their own project name, but for the details of this licence to be a boilerplate copy from a well-known licence, or even a reference to this licence. A REL should support this, providing a means for licences to be defined by sub-classing existing licences and possibly changing their behaviour.
Specific licences
These are licences that are created as needed, for specific pieces of content, or specific end users. This is usually so that they may have use-specific conditions attached to them, such as expiry dates. Although these licences might be based on a standard boilerplate, each one is thus unique. Referring to them by name could not work as there's no single, stable name. It's thus necessary to use a REL to express each one in terms of its individual properties.
Structure of a REL
A REL may conveniently use an Entity-Attribute-Value modelEntity-Attribute-Value modelEntity–attribute–value model is a data model to describe entities where the number of attributes that can be used to describe them is potentially vast, but the number that will actually apply to a given entity is relatively modest. In mathematics, this model is known as a sparse matrix...
, as for RDFResource Description FrameworkThe Resource Description Framework is a family of World Wide Web Consortium specifications originally designed as a metadata data model...
, to structure its description of a rights model. Such a model expresses iself as lists of:
Entities- Concrete "things" or "classes", e.g.:
- Work
- The item being licensed.
- Licence
- The licence, particularly when this is either a "well-known" licence (where many Works will use a comparable abstract licence, such as GFDL)
- or else an instance of a specific licence, such as content playback rights purchased by one user.
- End-user
- A means to identify the end-user, when the licensing is a specific contract with one person or body.
- JurisdictionJurisdictionJurisdiction is the practical authority granted to a formally constituted legal body or to a political leader to deal with and make pronouncements on legal matters and, by implication, to administer justice within a defined area of responsibility...
- Jurisdiction
- Rarely stated explicitly, but an important qualifier when there are local legal variations in IP lawIntellectual propertyIntellectual property is a term referring to a number of distinct types of creations of the mind for which a set of exclusive rights are recognized—and the corresponding fields of law...
.
Attributes- "Properties", or aspects of each of these Entities, e.g. for a Licence:
- constraints
- Actions that are either permitted, or forbidden
- Some RELs separate these constraints into groups, as the likely values for each are generally disjoint sets (actions that may be sometimes prohibited are rarely compulsory)
- permissions
- requirements
- prohibitions
Values- Values for these properties, from a pre-defined vocabulary, e.g. the Four Freedoms:
- Using the Work
- Studying and modifying the Work
- Redistributing copies
- Redistributing modified copies
The REL defines sets of members for each of these three groups, and the permitted relations between them. In the example above there may be concepts of Licences, permissions and redistributing copies. Also there may be the relations, A Licence may express prohibitions, and separately Permission may be given to redistribute copies.
Statements may then be made using the REL (these would be outside of the REL itself) such as:
This defines a new abstract licence, one that permits re-distribution of copies. Works may then use this Licence by referring to it,
This web page is licensed under >FooCo's Distribution Permitted Licence.
Note that although this hypothetical "Distribution permitted" licence has been expressed using the Creative Commons REL, it is not a Creative Commons licence. It merely uses the concepts "License", "permission" and "Distribution". Although it's not one of the Creative Commons licences defined by that project, it does share exact commonality for these terms: "Distribution" has exactly the same meaning and legal definition between them.
Interworking between licences
Increasing interest in mashupMashup (digital)A digital mashup usually is in reference to:1. Digital media content containing any or all of text, graphics, audio, video and animation drawn from pre-existing sources, to create a new derivative work...
s and collaborative projects creates a demand for combining content, and in licensing technologies that can support this.
The simplest approach is to only combine content under the same well-known licence. This is over-restrictive though, and many compatible licences may permit their content to be combinedLicense compatibilityLicense compatibility refers to the problem with licenses applied to works subject to copyright, particularly licenses of software packages, which can contain contradictory requirements, rendering it impossible to combine source code from such packages or content from such works in order to create...
. It is however difficult to judge this, whether it is permitted and how the resultant content should be licensed. There may still be subtleties when there are overlapping requirements or CopyleftCopyleftCopyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
issues. Notably the Creative Commons 'attribution-sharealike' and 'attribution-noncommercial-sharealike' are incompatible.See Creative Commons#Criticism
Combining licences is simpler if all of the licences involved may be expressed through the same REL. In that case it's easier to see when a permission or a prohibition applies if they do at least apply to an identical definition of "Distribution". An obvious example of this are the Creative Commons licensesCreative Commons licensesCreative Commons licenses are several copyright licenses that allow the distribution of copyrighted works. The licenses differ by several combinations that condition the terms of distribution. They were initially released on December 16, 2002 by Creative Commons, a U.S...
, where a family of licences are all defined in terms of the same REL.
Even if different licences were originally defined through different REL, it may be possible to re-encode a licence simultaneously in another shared REL, making them comparable. GPL has recently been expressed in ccREL, giving this advantage.Note that despite the suggestion of Introducing RDF for GNU Licenses, the benefit accrues because GPL is expressed in ccREL (and RDF), not merely in RDF. For licences to become comparable, the REL vocabularies must be shared, not merely the data model.
Difficulties in interworking between licences
Apart from the issues of conflicting requirements (above), there are also technical issues in comparing licences. Many of these are alleviated if the same REL can be used, even if the licences are different.
Semantics
A regular problem with semantic translationSemantic translationSemantic translation is the process of using semantic information to aid in the translation of data in one representation or data model to another representation or data model...
between schemas (such as RELs) is in making sure that the meanings of terms are identical. Although the semantic webSemantic WebThe Semantic Web is a collaborative movement led by the World Wide Web Consortium that promotes common formats for data on the World Wide Web. By encouraging the inclusion of semantic content in web pages, the Semantic Web aims at converting the current web of unstructured documents into a "web of...
is beginning to use ontology tools such as OWLWeb Ontology LanguageThe Web Ontology Language is a family of knowledge representation languages for authoring ontologies.The languages are characterised by formal semantics and RDF/XML-based serializations for the Semantic Web...
to describe meaning, the current state of the art for REL is less advanced than this. Simpler processing, and the potential for expensive litigation otherwise, means that the semantics of RELs must be clearly identical, not just inferred to be so through a reasonerSemantic reasonerA semantic reasoner, reasoning engine, rules engine, or simply a reasoner, is a piece of software able to infer logical consequences from a set of asserted facts or axioms. The notion of a semantic reasoner generalizes that of an inference engine, by providing a richer set of mechanisms to work with...
.
The regular problems are in demonstrating the equivalence of classes, properties and instances. For RELs the major problem is for the instances, i.e. the precise definitions of "Distribution", "Share-alike" etc. The classes and properties are usually simple concepts and very similar. Not all RELs support all classes though: some ignore Jurisdiction or even End-user, according to the needs of the market they were developed for.
Implicit pre-conditions
A less-obvious problem in comparing RELs is when they have a differing baseline. The baseline defines the conditions implied by the licence when there are no explicit statements included. Some RELs take the "Everything not permitted is forbidden" approach, others (such as ccREL) use the Berne ConventionBerne Convention for the Protection of Literary and Artistic WorksThe Berne Convention for the Protection of Literary and Artistic Works, usually known as the Berne Convention, is an international agreement governing copyright, which was first accepted in Berne, Switzerland in 1886.- Content :...
as their baseline. - Part 5 of this MPEG