From the conceptualisation, implementation and evaluation work, it is possible to conclude that the main hypotheses have been correctly posed. The Semantic Web tools allow facing the Digital Rights Management problem with an additional set of features, in comparison to the more common XML tools. These new features make possible to develop more complete domain models and facilitate the implementation of DRM applications.
The limitations of the current approaches are overcome by the ontology-based approach. The increased expressivity level allows formalising a greater part of the domain semantics, in this case of the copyright domain. Once formalised, this semantics are easier to implement, as it has been shown in the Evaluation chapter, e.g. the benefits of semantic queries versus syntactic ones like XPath.
Another consequence of grammar-based RELs expressiveness limitations is that they do not take into account the legal framework where the DRM systems that employ them operate. This is because the copyright legal framework is too complicated to be captured by syntax-based tools. However, as it has been shown in the Conceptualisation chapter, it is possible to develop a conceptual framework for both the legal and DRM parts of the domain, i.e. the contributed Copyright Ontology.
Moreover, the model expressivity solves the current RELs problem with the level of detail they have to support in order to cope with usage control. They have to specify every possible allowable usage in their grammar, or at least provide expansion points for this. Ontologies provide generalisation mechanisms and they can cope simultaneously with many levels of detail, as it is required by the rights situation at hand.
This kind of complex conceptual models can also be implemented using syntactic-approaches, but most of their semantics is lost from the formalisation point of view. The consequence of these limitations uses to be that the legal part of the model is not included in the implemented version and even ignored during the corresponding conceptualisation phase, as it is has been shown in the Rights Expression Languages chapter.
On the contrary, if the conceptual model is implemented using ontologies, a greater part of the model semantics can be captured. A Semantic Web based implementation of this model has been carried out. It is based on the Web Ontology Language (OWL) and, although it is not the more expressive ontology language available, it has shown its practical benefits.
The OWL implementation of the Copyright Ontology integrates the legal and DRM aspects. Moreover, its particular approach makes an extensive use of OWL classes as patterns for rights, licenses and usages modelling. With this approach, it is possible to reduce checking uses against rights and licenses to computing class subsumption and instance classification. These computations are tractable and decidable in the context of Description Logics, a family of logics that includes OWL-DL, the OWL sublanguage employed during the implementation.
Therefore, the implementation can be based on existing Description Logic reasoners, which facilitate the development of semantics-based DRM systems. This implementation approach has been sketched in the Implementation chapter and it has been put into practice in the Semantic DRM System section. Other benefits of the Semantic Web approach to DRM are shown in the Evaluation chapter. This chapter also includes the ontology versions of the main REL initiatives that allow performing an extensive evaluation of the Copyright Ontology in the context of real-world DRM requirements.
These practical results have been contributed to the MPEG-21 standardisation initiative for a DRM framework, as it is detailed in the Publications section. Moreover, in this section it is shown how the entire contribution has been validated in the forum of relevant international conferences and standardisation bodies.
To conclude, and from a more general point of view, it has been possible to observe the potential of Knowledge Representation in the Web context. The Semantic Web approach is being applied to very diverse application domains, e.g. e-science, e-commerce, business integration, recommendation systems or social networks. This work shows that it is also useful in the Digital Rights Management domain.
Just from the beginning, the research work has been validated against the research community in the context of relevant conferences and standardisation initiatives.
The contributions to standardisation bodies are centred on the MPEG-21 standardisation process. This initiative tries to define a complete content management framework that includes a complete digital rights management solution. The first contributions to MPEG-21 related to this work is a previous version of the Copyright Ontology, IPROnto, contributed as a complete solution for the MPEG-21 call for contributions for a Rights Expression Language and Rights Data Dictionary [MPEG01]:
After this initial contribution, there have been many others related to the use of Semantic Web tools for implementing MPEG-21 reference software. Moreover, it has been possible to evaluate the standard using a Web ontology, RDDOnto. The validation of the RDD ontology has shown many inconsistencies in the standard that have caused a standard corrigendum [Barlas05] and have recently opened another revision of the standard.
These are the publications resulting from the contribution of results related to this work to international conferences and workshops. They are related to different aspects of this work: the Copyright Ontology, the Semantic Web approach to DRM in general, semantic DRM systems, agents-mediated copyright negotiation and the XML Semantics Reuse methodology.
These publications are mainly related to the Copyright Ontology. The Copyright Ontology has been discussed in the main international conferences and workshops dealing with the legal ontologies, legal knowledge, regulatory ontologies and Semantic Web topics.
These publications include contributions mainly related to the general benefits of the Semantic Web approach for existing rights expression languages. They have been contributed to international conferences and workshops dealing with the legal ontologies and e-commerce fields. There is also a contribution to the ODRL Workshop, which is the main discussion forum for research related to this REL.
The following publications are mainly related to the development of semantics-enabled DRM systems. They have been presented in the context of international conferences and workshops dealing with sematic information systems, e-commerce and Semantic Seb.
The main research area of these publications is the area of artificial agents. They are applied in order to enable automatic and assisted negotiation of copyrighted works in the context of semantic DRM systems. They have been contributed to different editions of one of the main international conferences on agents for e-commerce applications.