Resource Description Framework

What is RDF?

- RDF stands for Resource Description Framework
- RDF is for describing resources on the web
- RDF is designed to be read by computers
- RDF is not designed for being displayed to people
- RDF uses URIs to identify web resources
- RDF uses property values to describe web resources
- RDF uses the terms resources, properties, and values
- RDF also uses the the terms subject, predicates and objects
- RDF is written in XML
- RDF is a web standard

RDF is Designed to be Read by Computers

RDF was designed to provide a common way to describe information so it can be read (and understood) by computer applications.
RDF descriptions are not designed to be displayed on the web.

RDF is Written in XML

Exemple of RDF file wich is written in XML - Example

As you can see from the example above, an RDF document is written in XML. The XML language used by RDF is called RDF/XML.
By using XML, RDF information can easily be exchanged between different types of computers using different types of operating system and application languages.


Why Not Just Use XML?

XML allows you to invent tags, which may contain both text data and other tags. XML has a built-in distinction between element types, for example the IMG element type in HTML, and elements, for example an individual <img src='Madonna.jpg'>; this corresponds naturally to the distinction between Properties and Statements. So it seems as though XML documents should be a natural vehicle for exchanging general purpose metadata.
XML, however, falls apart on the Scalability design goal.
There are two problems:
1. The order in which elements appear in an XML document is significant and often very meaningful. This seems highly unnatural in the metadata world. Who cares whether a movie's Director or Title is listed first, as long as both are available for lookups? Furthermore, maintaining the correct order of millions of data items is expensive and difficult, in practice.
2. XML allows constructions like
<Description>The value of this property contains some
text, mixed up with child properties such as its temperature
(<Temp>48</Temp>) and longitude
(<Longt>101</Longt>). [&Disclaimer;]</Description>

When you represent general XML documents in computer memory, you get weird data structures that mix trees, graphs, and character strings. In general, these are hard to handle in even moderate amounts, let alone by the billion.
On the other hand, something like XML is an absolutely necessary part of the solution to RDF's Interchange design goal. XML is unequalled as an exchange format on the Web. But by itself, it doesn't provide what you need in a metadata framework.

Getting started with RDF

Since RDF became a W3C Recommendation in February 1999, a number of tools have been created by developers working with RDF. For an in-depth treatment of these, consult the W3C RDF home page. A number of other listings are available, including XML.com, XMLhack and Dave Beckett's RDF Resource Guide.

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