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

The XML format provides the flexibility to describe anything, but it is also prone to errors and miscommunication. Find out how Resource Description Framework (RDF) can be a solution to these limitations.


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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