The objective of this work is to make a new contribution to the Digital Rights Management (DRM) research field. There are different initiatives trying to solve the problem of interoperability between DRM Systems (DRMS), which have started from isolated and proprietary initiatives. However, they are lately clearly moving to a web-broad application domain.
One of the main initiatives is MPEG-21 [Walle05], an ISO/IEC standardisation framework for digital content management. MPEG's DRM modelling part is divided into the Rights Expression Language (REL) and the Rights Data Dictionary (RDD) [Wang05]. Another initiative is ODRL (Open Digital Rights Language), available also as W3C note [Iannella02], that has been adopted by the Open Mobile Alliance (OMA) as a standard for the mobile communications field.
There are many other initiatives but, basically, all have one thing in common, they work at the syntactic level. Their approach is to define some XML Schemas that specify the grammar of rights expression languages (REL). In some cases, the semantics of these languages, i.e. the meaning of the expressions, are also provided but formalised separately as rights data dictionaries (RDD). Rights dictionaries list terms definitions in natural language, solely for human consumption and not easily automatable.
However, the syntactic approach does not scale well in really wide and open domains like the Internet. Automatic processing of huge amounts of metadata coming from many different sources requires machine understandable semantics. The syntax is not enough when unforeseen expressions are met. Here is where semantics come to help their interpretation to achieve interoperation.
There are other initiatives that have also chosen a semantic approach for DRM. The Harmony project [Hunter03] integrates copyright concepts from the MPEG-21 RDD into a generic ontological framework and OREL [Qu04] is also a formal ontology version of MPEG-21 RDD. However, these initiatives do no take into account the copyright legal framework, as the DRM initiatives they are based on do not consider this aspect either. On the other hand, there is the Creative Commons initiative [Lessig03], which is also based on semantic metadata but it does consider the legal framework. In this case, the inconvenient is that it provides a very simple formalisation intended for open release environments, e.g. open source software.
The proposed approach is to facilitate the automation and interoperability of DRMS integrating both parts, the Rights Expression Language and the Rights Data Dictionary. This objective can be accomplished using ontologies, which provide the required definitions of the rights expression language terms in a machine-readable form. Thus, from the automatic processing point of view, a more complete vision of the application domain is available and more sophisticated processing can be carried out.
The selected ontologies are those from the Semantic Web approach [Berners-Lee01] because they are naturally prepared for the Web domain, they are called web ontologies [Hendler01]. The modularity of web ontologies, constituted by concept and relation definitions openly referenceable as URIs, allows their easy extension and adaptation to meet evolvability and interoperability.
The contributed web ontology that formalises copyright law aspects is based on the World Intellectual Property Organisation (WIPO) recommendations, which try to define a common worldwide legal framework. Using a so general framework helps building a general copyright ontology, which can be then concretised for specific law systems. In any case, the current tendency is to adapt local copyright systems to this international framework. This facilitates the interrelations among these legal systems as they are being forced to interoperate due to copyright globalisation.
A preliminary version of this ontology, called IPROnto (Intellectual Property Rights ONTOlogy), was contributed [Delgado01a] to MPEG-21 REL-RDD call for proposals [MPEG01].
This document is organised as follows: after the introduction, the state of the art section analyses the four pillars on top of which this research work has been carried out. First, there is the Knowledge Representation chapter. Its content is grounded in a definition of knowledge and then moves to how knowledge is formalised with Knowledge Representation techniques. Nowadays, they have been combined with computation resources so this first state of the art section ends with an analysis of knowledge representation technologies.
Second, the state of the art focus moves to the Web. A short description is done centred on its foundation technologies. The main attention is placed on some actual web scenarios that highlight some of its problems. Then, some recent attempts from the Web community to reduce these problems are presented. They are a set of technologies based on the Web Services model.
Then, the third chapter of the state of the art explains the Semantic Web initiative as a combination of the previous Web and Knowledge Representation ideas. The Semantic Web is presented as an attempt to complete the work initiated by the Web initiative in order to overcome its problems. The complete set of design principles is shown and the architecture were they are been realised is detailed. Finally, the Web Services model is reconsidered complemented by the Semantic Web perspective.
The state of the art finishes with a chapter devoted to rights expression languages (RELs), which are the representational part of digital rights management systems. RELs are mainly based on syntactic approaches, i.e. a grammar defines the language elements. Their focus is on modelling the kind of licenses established by media distributors and end-users, which grant them permission for concrete actions under some conditions and constraints. Therefore, they do not deal with the underlying copyright law framework.
Once the research domain picture has been built, the objectives and the methodology are described in the preparatory part. They guide the research work that has been done in the contribution part. This part documents the development process of the main contribution of this work, the copyright ontology, as a conceptual and computable model.
It also includes an evaluation chapter with additional contributions geared towards demonstrating the benefits of the Semantic Web approach to the other REL initiatives and how their integration with the copyright ontology helps checking its validity.
Finally, the conclusions and the future work are presented. The conclusions section reviews the objectives and hypothesis in order to show how they have been fulfilled and confirmed during the contribution part of the work. Moreover, the conclusions detail all refereed publications and contributions to DRM standards that have allowed discussing these contributions in relevant international forums.