How RDF Beats Basic XML: Web-Based Data Sharing : Page 2

How Does RDF Work?

RDF works by expressing statements about resources, which can be anything. A resource does not even have to exist. One can describe whatever one wants to in RDF by putting together an RDF statement about that resource. In theory, a single RDF statement resembles a simple English sentence. For example, a typical simple English sentence is structured in the following way: Subject-Verb-Object. A typical RDF statement is made up of the three following components: Subject-Predicate-Object. These Subject-Predicate-Object triples are often referred to as just that: RDF triples.

The Subject is always a web resource. In RDF, a resource is represented by a URI. Unlike a URL, a URI is not used to locate resources, only to identify them (hence the I for Identifier instead of the L for Locator). A Predicate describes the Subject (an example of this is upcoming). Finally, the Object can be either another resource or a simple constant, possibly representing a number, string or date.

The expression "Alex is writing an article" would look something like this in an RDF triple:

Alex isWriting Article 

While the triples concept is intuitive because of its close relation to English, RDF syntax is a bit cryptic because it is meant for machine readability. In recent years, more human-readable RDF syntaxes have been introduced, but simple statements can still produce bulky and cryptic XML. For example, here is a snippet of real RDF that represents the simple expression "Alex is writing an article":

<RDF:RDF
    xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:j.0="http://www.w3.org/2001/XMLSchema#"
    xmlns:socterms="http://semanticalley.com/onto/2009/socrates#"
    xmlns:RDFS="http://www.w3.org/2000/01/rdf-schema#"
    xmlns:RFDExample="http://semanticalley.com/onto/2009/rdfExample#" >
  <RDF:Description RDF:about="http://semanticalley.com/onto/2009/rdfExample#Alex">
    <RFDExample:isWriting RDF:resource="http://semanticalley.com/onto/2009/rdfExample#Article
    <RDF:type RDF:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  </RDF:Description>
  <RDF:Description RDF:about="http://semanticalley.com/onto/2009/rdfExample#Article">
    <RDF:type RDF:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  </RDF:Description>
  <RDF:Description RDF:about="http://semanticalley.com/onto/2009/rdfExample#isWriting">
    <RDF:type RDF:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate"/>
  </RDF:Description>
</RDF:RDF>

Ultimately, the size and complexity of the XML is not a huge concern because the cryptic syntax is meant for computers. Also because it is meant for machines, one can put together large collections of statements. A large and/or comprehensive collection of statements about a subject (such as wine for example) is a body of data that in the philosophy of knowledge is known as an ontology. Hence, in Semantic Web, one can make ontologies in RDF and infinitely share them.

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