RDF

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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).

[edit] Basic ideas

RDF is a general method to decompose any type of knowledge into small pieces, with some rules about the semantics, or meaning, of those pieces. The point is to have a method so simple that it can express any fact, and yet structured enough that computer applications can do useful things with it.

Here are some introductory texts:

And some more extensive information:

[edit] Overview of RDF

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:

  • Resources
  • Properties
  • Statements

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
Resource rdf:subject an apple
Property rdf:predicate is a
Resource rdf:object fruit

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

[[subclass of::Fruit]]

within the article Apple.

[edit] See also

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