RDF

Draft

Definition

• The Resource Description Framework (RDF) is a language for representing information about resources in the World Wide Web.

• Originally RDF was primarily intended to represent metadata about Web resources, such as the title, author, and modification date of a Web page, copyright and licensing information about a Web document, or the availability schedule for some shared resource. However, by generalizing the concept of a "Web resource", RDF can also be used to represent information about things that can be identified on the Web, i.e. the semantic web.

Major RDF vocabularies

Metadata

• Learning Object Metadata Standard
• Dublin Core

Content syndication and social software

• RSS 1.0 which is not very popular, most RSS formats are not RDF since bloggers don't understand issues related to the semantic web :)
• FOAF Friends-of-a-friend vocabulary for person networks

Semantic Web

• OWL
• SKOS (Simple Knowledge Organisation System)
• SPARQL (Query language)

RDF basics

At its core, RDF has a simple relational data model: Subject - Verb - Object or expressed differently Predicate (Subject, Object)

• Subject = The resource
• Object = Value
• Verb = Predicate = propriety = relation of the subjet with the object

Here is a typical RDF fragment

<?xml version="1.0"?>
 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
          xmlns:mon_schema="http://tecfa.unige.ch/lib/mon_schema" >
 <rdf:Description rdf:about="http://tecfa.unige.ch/perso/staf/lattion/">
  <mon_schema:Creator>Stéphane Lattion</mon_schema:Creator>
 </rdf:Description>
</rdf:RDF>

It expresses a relation like this:

A simple ressource-author relationship

RDF and the semantic web

The RDF Software stack

The RDF software stack

The RDF bus

Software clients of the RDF bus

Turtle syntax

Since XML/RDF code is some verbose, writing it manually is fairly time consuming. The W3C team proposes a "textual syntax for RDF called Turtle that allows RDF graphs to be completely written in a compact and natural text form, with abbreviations for common usage patterns and datatypes" (Turtle - Terse RDF Triple Language, retrieved 15:31, 10 March 2008 (MET)).

Example:

<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/dc/elements/1.1/"
         xmlns:ex="http://example.org/stuff/1.0/">
  <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"
		   dc:title="RDF/XML Syntax Specification (Revised)">
    <ex:editor>
      <rdf:Description ex:fullName="Dave Beckett">
	<ex:homePage rdf:resource="http://purl.org/net/dajobe/" />
      </rdf:Description>
    </ex:editor>
  </rdf:Description>
</rdf:RDF>

becomes in turtle syntax:

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
@prefix ex: <http://example.org/stuff/1.0/> .

<http://www.w3.org/TR/rdf-syntax-grammar>
  dc:title "RDF/XML Syntax Specification (Revised)" ;
  ex:editor [
    ex:fullname "Dave Beckett";
    ex:homePage <http://purl.org/net/dajobe/>
  ] .

Links

Standards

• Resource Description Framework (RDF) Overview
• Resource Description Framework (RDF): Concepts and Abstract Syntax, W3C Recommendation 10 February 2004
• Resource Description Framework (RDF) Model and Syntax.
• RDF Semantics, W3C Recommendation 10 February 2004 (rather difficult reading).
• RDF/XML Syntax Specification, W3C Recommendation 10 February 2004.
• RDF Vocabulary Description Language 1.0: RDF Schema, W3C Recommendation 10 February 2004
• Turtle - Terse RDF Triple Language

RDF Namespaces

• 100 most common RDF namespaces

RDF and XHTML

• See the RDFa article
• RDFa Primer 1.0 Embedding RDF in XHTML (Working Draft in March 2007)

OWL

• OWL Web Ontology Language Overview, W3C Recommendation 10 February 2004.
• OWL Web Ontology Language Guide, W3C Recommendation 10 February 2004
• OWL Web Ontology Language Semantics and Abstract Syntax, W3C Recommendation 10 February 2004
• Dean M., Schreiber G (Editors); van Harmelen F., Hendler J., Horrocks I., McGuinness D.L., Patel-Schneider P.F., Stein L.A. (Authors), OWL Web Ontology Language Reference, W3C Recommendation, 10 February 2004. HTML

Other RDF Applications

• SPARQL Query Language for RDF (W3C Recommendation, 15 January 2008)
• PICS (Platform for Internet Content Selection)
• SKOS Simple Knowledge Organization System (W3C WD Jan 2008)

Overviews

• Mozilla's RDF pointers
• Oasis Resource Description Framework (RDF)
• W3C Data Formats A older (1997) note on the planned XML-centered framework
• Chris Waterson, RDF in Fifty Words or Less, Mozilla Magazine.

On-line validation

• W3C RDF validation service

RDF-related web sites

• http://www.semanticplanet.com/
• W3C Semantic Web page.
• ontoworld.org

Various to sort out

• Supercharging WSDL with RDF Managing structured Web service metadata article by Uche Obbuji
• Rudolf: RDFViz Exploring tools for RDF Graph Visualisation by Dan Brickely, project page.

References

• Eric Miller An Introductionto the Resource Description Framework (1998), D-Lib Magazine May 1998, ISSN 1082-9873, HTML

• Manola Frank and Eric Miller (2004). RDF Primer, W3C Recommendation 10 February 2004, W3C.