Resource Description Framework or RDF is a family of specifications for a metadata model that is often implemented as an application of XML. The RDF family of specifications is maintained by the World Wide Web Consortium (W3C).
The idea behind RDF is to mark up elements written in XML with additional metainformation. It is build upon ideas from the AI science. Therefore the standard defines three fundamental concepts:
To show an example we take the statement "an apple is a fruit". We can break it into the following parts.
|Construct||RDF-Type||Part of the sentence|
Notice, the "an" in "an apple", which unlike "the", "this", "that", etc., defines not a specific object (instance), but a special kind of objects (class).
In a graphical representation this might look like this:
------- is a ------- | Apple |-------->| Fruit | ------- -------
In code it looks like:
<rdf:RDF> <rdf:Statement> <rdf:subject rdf:resource="Apple" /> <rdf:predicate rdf:resource="onto;is a" /> <rdf:object rdf:resource="Fruit" /> </rdf:Statement> </rdf:RDF>
(Note that there are less verbose ways of expressing this triple in RDF/XML and resources are URIs.)
The SMW equivalent of this is the code
within the article Apple.