RDF

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1 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.

2 Major RDF vocabularies

Metadata

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)

3 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

4 RDF and the semantic web

4.1 The RDF Software stack

The RDF software stack

4.2 The RDF bus

Software clients of the RDF bus

5 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/>
  ] .

6 Links

6.1 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)

6.2 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.

6.3 On-line validation

W3C RDF validation service

6.4 RDF-related web sites

6.5 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.

7 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.

RDF

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