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Created: August 22, 2008.
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W3C Member Submission for Creative Commons Rights Expression Language (ccREL).


On August 20, 2008 W3C published the text of a Member Submission from Creative Commons: ccREL: The Creative Commons Rights Expression Language. The paper introduces a standard recommended by Creative Commons (CC) for machine-readable expression of copyright licensing terms and related information. ccREL is a major update of the earlier work of Creative Commons, proposing an annotation mechanism for expressing licenses of resources on the Web.

The Creative Commons Rights Expression Language (ccREL) builds upon the astronomical success of Creative Commons licenses. CC licenses are embeddable machine-readable legal instruments allowing authors to express permissions for others to share, remix, and reuse content. Melissa Reeder (Creative Commons Development Manager) recently wrote in a newsletter:

[that] websites, technology companies, and media sharing platforms are now implementing CC-licensing tools inside their systems. Flickr is a great example of how sites that offer the easy ability to attach Creative Commons licenses to content are immensely useful in growing the commons. By current count, there are more than 77 million Flickr photos under CC licenses. This an incredible number, and this success is largely due to the fact that Flickr offers a simple and intuitive interface for adding CC licenses to photos, as well as very clear messaging about how Creative Commons works..."

Supported by free tools, the Creative Commons licenses let authors, scientists, artists, and educators easily mark their creative work with the freedoms they want it to carry. Creative Commons licenses are expressed in three different formats: the Commons Deed (human-readable code), the Legal Code (lawyer-readable code); and the metadata (machine-readable code). One need not sign anything to get a Creative Commons license: you just select a license and incorporate relevant declaration into the online resource (text, audio, video, image, interactive). Each license helps the creator retain copyright and announce that other people's fair use, first sale, and free expression rights are not affected by the license.

In addition to a CC Public Domain Dedication and software licenses, the six principal Creative Commons Licenses are as follows:

  • Attribution (by) — lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit you for the original creation.

  • Attribution Share Alike (by-sa) — lets others remix, tweak, and build upon your work even for commercial reasons, as long as they credit you and license their new creations under the identical terms; this license is often compared to open source software licenses.

  • Attribution No Derivatives (by-nd) — allows for redistribution, commercial and non-commercial, as long as it is passed along unchanged and in whole, with credit to you.

  • Attribution Non-commercial (by-nc) — lets others remix, tweak, and build upon your work non-commercially, and although their new works must also acknowledge you and be non-commercial, they don't have to license their derivative works on the same terms.

  • Attribution Non-commercial Share Alike (by-nc-sa) — lets others remix, tweak, and build upon your work non-commercially, as long as they credit you and license their new creations under the identical terms; others can download and redistribute your work just like the by-nc-nd license, but they can also translate, make remixes, and produce new stories based on your work.

  • Attribution Non-commercial No Derivatives (by-nc-nd) — the most restrictive of our six main licenses, allowing redistribution; this license is often called the 'free advertising' license because it allows others to download your works and share them with others as long as they mention you and link back to you, but they can't change them in any way or use them commercially.

As summarized in the W3C Team Comment on ccREL, the Creative Commons Rights Expression Language "provides a comprehensive approach, covering an abstract model using RDF, a definition of basic properties and classes that can be extended and reused by third parties, and recommended practices to serialize this abstract model. The abstract model separates the concept of License, which can be characterized by a number of predefined properties with possible values, and so called 'work properties', i.e., properties that relate a specific work to a specific instance of a License. ccREL is firmly rooted in RDF, meaning that the various syntax possibilities for ccREL are also bound to possible RDF serializations. For (X)HTML documents, RDFa is the preferred serialization format (discontinuing the previous practice of adding RDF/XML code as an HTML comment in the HTML source), and the document gives several examples of how to do that in practice. For other document formats, usage of GRDDL, direct embedding of RDF data, XMP, etc, are also described. The separation of the abstract RDF-based model from the specific syntax is rewarded insofar as many different syntaxes become possible depending on the underlying Web resource format. This is also a major step forward compared to the earlier Creative Common license recommendations..."

"The latest versions of the well-known Creative Commons licenses are all instances of License; however, and therein lies one of the important new features of ccREL: by defining those in terms of specific RDF properties, third parties can define their own variants of License and combine those with the rest of the general ccREL framework. Also, automation can be built to interpret other licenses that re-use the same properties... Publishers have wide discretion in their choice of syntax, so long as the process for extracting the properties is discoverable and tool builders can retrieve the properties of ccREL-compliant Web pages or embedded documents..."

The ccREL specification also recommends specific concrete default syntaxes and embedding schemes for content creators and publishers who want to use CC licenses without needing to be concerned about extraction mechanisms. The default schemes are RDFa for HTML Web pages and resources referenced therein, and XMP for stand-alone media.

"One consequence of CC's limited initial design is that, although millions of Web pages now include Creative Commons licenses and metadata, there is no uniform, extensible way for tool developers to access this metadata, and the tools that do exist rely on ad-hoc techniques for extracting metadata. Compared to the previous recommendation, ccREL is intended to be both easier for content creators and publishers to provide, and more convenient for user communities and tool builders to consume, extend, and redistribute. An earlier recommendation from Creative Commons was supported by a generator that created provided RDF/XML text for inclusion inside HTML comment declarations. As described in ccREL, Creative Commons no longer recommends using RDF/XML in HTML comments for specifying licensing information. However, all first-generation licenses are still correctly interpretable against the new specification, thanks in large part to the extensibility properties of RDF itself.

"Creative Commons wants to make it easy for artists and scientists to build upon the works of others when they choose to: licensing your work for reuse and finding properly licensed works to reuse should be easy. The major goal of the ccREL technological approach is to make it easy to publish and read rights expression data now and in the future, when the kinds of licensed items and the data expressed about them goes far beyond what we can imagine today. By using RDF, ccREL links Creative Commons to the fast-growing RDF data interoperability infrastructure and its extensive developer toolset: other data sets can be integrated with ccREL, and RDF technologies, e.g. data provenance with digital signatures, can eventually benefit ccREL..."

Creative Commons developers believe that "the technologies we have selected for ccREL will enable the kind of powerful, distributed technological innovation that is characteristic of the Internet. Anyone can create new vocabularies for their own purposes and combine them with ccREL as they please, without seeking central approval. Just as we did with the legal text of the licenses, we aim to create the minimal infrastructure required to enable collaboration and invention, while letting it flourish as an organic, distributed process. We believe ccREL provides this primordial technical layer that can enable a vibrant application ecosystem, and we look forward to the community's innovative ideas that can now freely build upon ccREL."

Section 7 of the ccREL specification discusses "How Tool Builders Can Use ccREL," with reference to the 'MozCC' Mozilla Add-On and 'Operator' Firefox Add-On. "MozCC processes pages by listening for load events and then calling one or more metadata extractors on the content. Metadata extractors are JavaScript classes registered on browser startup; they may be provided by MozCC or other extensions. MozCC ships with extractors for all current and previous Creative Commons metadata recommendations, in particular ccREL..." [and] "Operator detects microformats and RDFa in the web pages a user visits. Operator can be extended with 'action scripts' that are triggered by specific data found in the web page. The regions of the page that contain data are themselves highlighted so that users can visually detect and receive contextual information about the data. It is relatively straight-forward to write a Creative Commons action script that finds all Creative Commons licensed content inside a web page by looking for the RDFa syntax..."

Comment from the W3C Team on the ccREL submission identifies several relationships to W3C Activities, including PLING and Protocol for Web Description Resources (POWDER): "The RDF aspects of the Creative Commons infrastructure are clearly an integral part of the Semantic Web landscape, including the Linking Open Data cloud. As such, this Member Submission is obviously related to the Semantic Web Activity. As a policy language, ccREL is also related to the work done by the Policy Languages Interest Group (PLING). ccREL is a clear application use case for a future trust/provenance infrastructure for the Semantic Web. A solution in this area should cover some of the problems raised by the usage of ccREL. As such, this Submission should play an integral part in any work in this area as a major use case. W3C does not yet have a timetable for starting this work... ccREL is also a clear use case for the POWDER work. Although the formal POWDER Use Case document will not necessarily change in future, ccREL should certainly be made known to the POWDER group as an important practical example for their technology."

Bibliographic Information

The ccREL Abstract Model

"Creative Commons' new recommendation for machine-readable licensing information, in its abstract form, i.e., independent of any concrete syntax. As an abstract specification, ccREL consists of a small but extensible set of RDF properties that should be provided with each licensed object. The abstract model for ccREL distinguishes two classes of properties:

  1. Work properties describe aspects of specific works including under which license a Work is distributed
  2. License properties describe aspects of licenses

Publishers will normally be concerned only with Work properties: this is the only information publishers provide to describe a Work's licensing terms. License properties are used by Creative Commons itself to define the authoritative specifications of the licenses we offer. Other organizations are free to use these components for describing their own licenses. Such licenses, although related to Creative Commons licenses, would not themselves be Creative Commons licenses nor would they be endorsed necessarily by Creative Commons.

Work Properties: "A publisher who wishes to license a Work under a Creative Commons license must, at a minimum, provide one RDF triple that specifies the value of the Work's license property (i.e., the license that governs the Work)... Although this is the minimum amount of information, Creative Commons also encourages publishers to include additional triples giving information about licensed works: the title, the name and URL for assigning attribution, and the document type.

New properties may be added over time, defined by Creative Commons or by others. Observe that ccREL inherits the underlying extensibility of RDF — all that is required to create new properties is to include additional triples that use these. For example, a community of photography publishers could agree to use an additional photoResolution property, and this would not disrupt the operation of pre-existing tools, so long as the old properties remain available..."

License Properties: "With ccREL, Creative Commons does not expect publishers to use these license properties directly, or even to deal with them at all. Tool builders, on the other hand, should take these License properties into account so that they can interpret the particulars of each Creative Commons license. The License properties governing a Work will typically be found by URL-based discovery. A tool examining a Work notices the xhtml:license property and follows the indicated link to a page for the designated license. Those license description pages — the "Creative Commons Deeds" — are maintained by Creative Commons, and include the license properties in the CC recommended concrete syntax (RDFa)...

As new copyright licenses are introduced, Creative Commons expects to add new permissions, requirements, and prohibitions. However, it is unlikely that Creative Commons will introduce new license property types beyond permits, requires, and prohibits. As a result, tools built to understand these three property types will be able to interpret future licenses, at least by listing the license's permissions, requirements, and prohibitions: thanks to the underlying RDF framework of designating properties by URLs, these tools can easily discover human-readable descriptions of these as-yet-undefined property values..."

Comment on the Submission from the W3C Team

Ivan Herman, Eric Prud'hommeaux, Thomas Roessler, and Rigo Wenning provided technical comment on the ccREL Member Submission. Excerpts:

Comments on the modeling approach: "The core of the current abstract model is to define RDF triples [...] relating some Web resource to a particular license (e.g., by encoding this triple in RDFa in the XHTML source of the Web document). An alternative might have been to use RDF typing instead [...] This approach would have made it possible to use the richer classification facilities of OWL to define more complex Licenses...

The OWL restriction idiom is used by POWDER to attach document properties to classes of resources. (Whether the attribution would then be added explicitly by the user or inferred by an OWL aware tool is a secondary question.) The usage of OWL might facilitate the modeling of a number of more complex features such as the definition of the disjointness of certain classes, or the usage of property characterization (functional, inverse functional, etc.). Tools could then detect possible contradiction more easily.

It must be said that using OWL, even a simple profile thereof, might be too complicated for the core constituency of ccREL, supporting the model in this Member Submission. We also recognize that such an approach would depart from the common usage of the XHTML license relation or Dublin Core's license term. Nevertheless, it may be worth considering this direction in the future if more complex licensing approaches are to be considered and developed..."

Comments on 'issues of the semantic system in general': "Some design choices of the Semantic Web lead to interesting interactions with the intended semantics of ccREL: RDF is designed to allow systems to get useful and reliable data without supporting all possible forms of inference. This is accomplished by making sure that any conclusions an application draws at one level of inference are still true when the application performs more inference.

The intended interpretation of ccREL licenses means that agents need to assume defaults on some properties. For example, the permission to use a work commercially is concluded from the absence of an explicit cc:prohibits property. Likewise, an agent will need to know the full set of cc:requires statements before it can conclude that it actually can and will fulfill all requirements that go along with the agent's intended use of the work.

In order to be able to draw these conclusions in a predictable way, an agent needs to work on an explicit RDF graph; the conclusions are then drawn limited to the scope of that graph. Speaking technically, ccREL as currently specified employs non-monotonic reasoning. To map this non-monotonic reasoning into RDF's monotonic semantic framework, the reasoning needs to be scoped to a specific context.

To establish such a context, ccREL could, e.g., specify that no additional reasoning is applied to the graph that describes a license, and limit the graph that is considered to the triples obtained by dereferencing the license URI. Given such an explicit rule, someone wanting a list of documents which can be used as the basis for derivative works could perform a SPARQL query..."

A note on using defaults: "The design pattern that we describe above enables transforming non-monotonic data into monotonic data, and is therefore safely usable by in the richer context of the Semantic Web. However, several key extension possibilities of the Semantic Web need to be restricted when using defaults:

  • inference: properties from RDFS and OWL may not be used to infer requires relationships as applications that don't perform exactly this inference will assume a contradictory default value
  • aggregation: while agents may trust more sources than are listed as authoritative, any of these may introduce contradictory statements which the system can not detect as contradictory
  • extensibility: applications designed to process extensions of a particular set of data will presume potentially incorrect default values when examining unextended data

While the trade-off between these restrictions and the use of defaults may very well be the right choice for the ccREL case, we recommend caution in other environments in which the Semantic Web's ability to extend and mix knowledge from different sources is beneficial to consumers of the data..."

About Creative Commons

"Creative Commons is a Massachusetts-chartered 501(c)(3) tax-exempt charitable corporation... Creative Commons defines the spectrum of possibilities between full copyright (all rights reserved) and the public domain (no rights reserved). Our licenses help you keep your copyright while inviting certain uses of your work: a 'some rights reserved' copyright.

"We use private rights to create public goods: creative works set free for certain uses. Like the free software and open-source movements, our ends are cooperative and community-minded, but our means are voluntary and libertarian. We work to offer creators a best-of-both-worlds way to protect their works while encouraging certain uses of them, to declare 'some rights reserved.' Thus, a single goal unites Creative Commons' current and future projects: to build a layer of reasonable, flexible copyright in the face of increasingly restrictive default rules..."

Creative Commons International (CCi) works to "port" the core Creative Commons Licenses to different copyright legislations around the world. The porting process involves both linguistically translating the licenses and legally adapting them to particular jurisdictions. The generic licenses are jurisdiction-agnostic: they do not mention any particular jurisdiction's laws or statutes or contain any sort of choice-of-law provision. The licenses are, however, based on the U.S. Copyright Act in many respects. This means that, though we have no reason to believe that the licenses would not function in legal systems across the world, it is at least conceivable that some aspects of our licenses will not align perfectly to a particular jurisdiction's laws...

ccLearn is a division of Creative Commons which is dedicated to realizing the full potential of the Internet to support open learning and open educational resources (OER). Our mission is to minimize barriers to sharing and reuse of educational materials — legal barriers, technical barriers, and social barriers... The availability of open educational content is growing exponentially, yet the usage of such content does not appear to be widespread. Worse, much of the OER currently being created is incompatible — legally, technically, and socially — with other OER. An immediate goal for ccLearn is to encourage and facilitate the adoption of practices that will enable the fullest realization of the potential for OER to transform education. ccLearn will leverage the unique capacity of Creative Commons to act upon this overarching view in a manner that popularizes the resources that already exist and brings new communities and groups into the world of open learning..."

Science Commons has three interlocking initiatives designed to accelerate the research cycle — the continuous production and reuse of knowledge that is at the heart of the scientific method. Together, they form the building blocks of a new collaborative infrastructure to make scientific discovery easier by design... We implement all three elements of our approach in the NeuroCommons, our 'proof-of-concept' project within the field of neuroscience. The NeuroCommons is a beta open source knowledge management system for biomedical research that anyone can use, and anyone can build on... The sciences depend on access to and use of factual data. Powered by developments in electronic storage and computational capability, scientific inquiry is becoming more data-intensive in almost every discipline. Whether the field is meteorology, genomics, medicine, or high-energy physics, research depends on the availability of multiple databases, from multiple public and private sources, and their openness to easy recombination, search and processing..."

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