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Tuesday, August 19, 2008

Resource Description Framework (RDF) - Enabling technology for the Semantic Web

Resource Description Framework (RDF)

An official W3C recommendation, RDF is an XML-based standard for describing resources that exist on the Web, intranets, and extranets. RDF builds on existing XML and URI (Uniform Resource Identifier) technologies, using a URI to identify every resource, and using URIs to
make statements about resources. RDF statements describe a resource (identified by a URI), the resource’s properties, and the values of those properties. RDF statements are often referred to as “triples” that consist of a subject, predicate, and object, which correspond to a resource (subject) a property (predicate), and a property value (object). Below is an example of an RDF statement in plain English:

.[resource].[property].[value].
.The secret agent.is.Niki Devgood.
.[subject].[predicate].[object].

RDF triples can be written with XML tags, and they are often conceptualized graphically as shown below:

graphical triples representation

After creating this triple, we can go on to create other triples to associate the agent with an email address, image, etc.


graphical triples representation

Once triples are defined graphically, they can be coded in either RDF/XML or n-Triples formats to be accessed programmatically.
By creating triples with subjects, predicates, and objects, RDF allows machines to make logical assertions based on the associations between subjects and objects. And since RDF uses URIs to identify resources, each resource is tied to a unique definition available on the Web. However, while RDF provides a model and syntax (the rules that specify the elements of a sentence) for describing resources, it does not specify the semantics (the meaning) of the resources. To truly define semantics, we need RDFS and OWL.

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