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Semantics Standards and Recommendations

owl rdf web language

Definition: The World Wide Web Consortium (W3C) began their semantic web activities in 2001 by introducing several semantic standards and recommendations, including Resource Description Framework (RDF) and Web Ontology Language (OWL) recommendations.

Beginning mostly in the late 1990’s, researchers began to focus on making their semantic tools’ syntaxes and semantics compatible with Internet technologies (e.g. XML, Uniform Resource Identifiers). This was necessary as data sources came online on a global scale, and were open for searching and retrieval by application programs. It was also the result of a challenge from Web visionary Tim Berners-Lee to create the Web’s next incarnation. The World Wide Web Consortium (W3C) began their semantic web activities in 2001. In parallel, other research influenced W3C’s directions, including: the Simple Hypertext Ontology Extensions (SHOE) and the DARPA Agent Markup Language (DAML). W3C’s work resulted in the Resource Description Framework (RDF) and Web Ontology Language (OWL) recommendations.

RDF is “intended to provide a simple way to make statements about Web resources (objects)”. With RDF, objects have properties which in turn have values. RDF uses the URI concept throughout, and while it admits to several concrete syntaxes, XML is the most prevalent. RDF statements are triples consisting of a resource, a property and a value (an English analogy: “John Smith edits the web page”). The RDF Schema (RDFS), a semantic extension of RDF, allows users to create rich vocabularies (for application domains) that can be used to describe properties of other RDF resources. Together, RDF and RDFS provide a previously unsupported semantics layer to XML and allow collaboration on a global scale (from previously closed-world approaches).

Built upon RDF, the W3C OWL Language was designed to provide more expressive power than RDF, to admit to a formal semantic, to enable reasoning, and to be widely distributed and scalable. Expressivity improvements resulted from OWL’s features beyond RDF’s fairly rudimentary ones (class, subclass, property, domain, range, etc.); these included concepts of class disjointedness, class union, cardinality restrictions and transitivity among others. OWL formal semantics and reasoning arose from the ability to map the language onto description logics. Already, OWL has interworked with various reasoning engines to provide compelling civilian and military applications (in line with Berners-Lee’s vision). Like RDF, OWL supports distribution via the ability to include and reference resources via URI and scalability through language constructs that allow metadata about classes and ontologies themselves (e.g. naming instances A and B from different ontologies as the “sameAs” each other). The following snippet of the OWL XML syntax illustrates a subclass definition (violin as a type of stringed instrument):

<owl:class rdf:ID=“violin”>
        <rdfs:subclassOf rdf:resource=“#stringedInstrument”/>

To satisfy a wide range of application requirements, W3C has proposed OWL in three progressively more powerful sublanguages named: OWL Lite, OWL DL, and OWL Full.

Semantics Web Tools and Technologies - Sesame, ICS-FORTH RDFSuite, Jena [next] [back] Semantic Web Services - Intelligent Web Services, Web Service Technology

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