humans to understand and applications to use. New reasoning services can be used to alert developers to unanticipated and/or undesirable interactions when modules are integrated and to identify a subset of the original ontology that is indistinguishable from it when used to reason about the relevant subset of the domain. ⁴

The availability of an SQL has been an important factor in the success of relational databases, and there have been several proposals for a semantic Web query language. As in the case of RDF and OWL, the W3C in 2004 set up a standardization working group that in January 2008 completed its work on the SPARQL query language standard ( www.w3.org/TR/rdf-sparql-que- ry). Strictly speaking, this language is only for RDF, but it is easy to see how it could be extended for use with OWL ontologies, something already happening in practice.

As I mentioned earlier, major research efforts have been directed toward tackling some of the barriers to realizing the semantic Web; considerable progress has been made in such areas as ontology alignment ( reconciling ontologies that describe overlapping domains), ¹⁸ ontology extraction (extracting ontologies from text), ¹⁶ and the automated annotation of both text⁶ and images. ⁵ Of particular interest is the growth of Web 2.0 applications, showing how it might be possible for user communities to collaboratively annotate Web content, as well as create simple forms of ontology via the development of hierarchically organized sets of tags, or folksonomies. ²¹ Progress has also been made in developing the infrastructure needed to add structured annotations to existing Web resources. For example, in October 2008 the W3C produced a Recommendation for RDFa, a mechanism for embedding RDF in existing XHTML documents ( www.w3.org/TR/rdfa-syntax/).

conclusion

Semantic Web research aims to help Web-accessible information and services be more effectively exploited, particularly by software agents and applications. As a first step, the W3C developed new languages, including RDF and OWL, that allow for the description of Web resources and the representation

of knowledge to enable applications to use resources more intelligently.

Although a wide range of semantic Web applications is available today, fully realizing the semantic Web still seems a long way off and would first require the solution of many challenging research problems, including those in knowledge representation and reasoning, databases, computational linguistics, computer vision, and agent systems. Moreover, most of the Web is yet to be semantically annotated, and relatively few ontologies are available (even fewer high-quality ones).

However, semantic Web research already has a major influence on the development and deployment of ontology languages and tools (often called semantic Web technologies). They have become a de facto standard for ontology development and are seeing increased use in research labs, as well as in large-scale IT projects, particularly those where the schema plays an important role, where information has high value, and where information may be incomplete. This emerging role is reflected in extended support for semantic Web technologies, including commercial tools, implementations, and applications, from commercial vendors, including Hewlett-Packard, IBM, Oracle, and Siemens.

Related challenges involve both expressive power and scalability. However, the success of the technologies also motivates research and development efforts in academic institutions and industry to address these challenges; it seems certain these efforts will have a major influence on the future development of information technology.

acknowledgment

I want to thank Uli Sattler of the University of Manchester and Franz Baader of Dresden Technical University for letting me borrow the idea of using Harry Potter in the ontology examples.

 

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Ian Horrocks ( [e-mail]) is a professor of computer science in the oxford university computing Laboratory and a fellow of oriel college, oxford, u.k.