RDF - Resource description Framework

URI - Uniform Resource Identifier 

A URI is a web identifier for example the strings starting http or ftp that you find on the world wide web. URIs can be created and owned by anyone, so they are the ideal base on which to build a world wide web on, in fact any thing with a URI can be said to be on the web.  The syntax of URI is governed by the IETF who have published documents with the exact URI specification.

How RDFs Work

A triple is described as three URIs. A language which utilizes triples in this way is called an RDF. XML has been created to be the recommended "syntax" of an RDF. XML essentially allows uses to create tags of hidden labels for there documents these tags can be attached to web pages or just areas of text. But in order for Scripts or programs to make use of these tags the script writer has to know what the page writer uses each tag for. RDF XML is considered to be the standard interchange format for an RDF on the semantic web, this does not make it the only format however another good example of a serialization of an RDF would be Notation 3. 

"The semantic will enable machines to comprehend semantic documents and data, not human speech and writings"  Scientific America : The Semantic Web

A quick example of something written in RDF XML:

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

     xmlns:dc="http://purl.org/dc/elements/1.1/"

     xmlns:foaf="http://xmlns.com/0.1/foaf/" > 

    <rdf:Description rdf:about=""> 

        <dc:creator rdf:parseType="Resource"> 

            <foaf:name>Sean B. Palmer</foaf:name> 

        </dc:creator> 

        <dc:title>The Semantic Web: An Introduction</dc:title> 

    </rdf:Description> 

</rdf:RDF>

This piece of RDF basically says that this article has the title "The Semantic Web: An Introduction", and was written by someone whose name is "Sean B. Palmer". Here are the triples that this RDF produces:-

This format is actually a plain text serialization of RDF called "Notation3". Note that some people actually prefer using XML RDF to Notation3, but it is generally accepted that Notation3 is easier to use, and is of course convertable to XML RDF anyway. (code taken from http://infomesh.net/2001/swintro/#whatIsSw [IN01]).

The triples of RDF form webs of information about related things. Because RDF uses URIs to encode this information in a document, the URIs ensure that concepts are not just words in a document but are tied to a unique definition that everyone can find on the Web. For example, imagine that we have access to a variety of databases with information about people, including their addresses. If we want to find people living in a specific zip code, we need to know which fields in each database represent names and which represent zip codes. RDF can specify that "(field 5 in database A) (is a field of type) (zip code)," using URIs rather than phrases for each term. Extract from Scientific America [SC01]

Why use RDF Rather than XML?

The answer to this is simple: by drafting a language in RDF one gets the benefit that the information is mapped directly and unambiguously onto a model, a model which is decentralized and a model for which there are many generic purposes.  This essentially means that one can distinguish between the parts that are the semantics and the bits that are just syntactic "fluff". And because RDF is so well known everyone can distinguish between them.  

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