RDF:The Resource Description Framework

Machine Understandable Metadata for the Web

Ralph R. Swickswick@w3.org

W3C/MIT2-November-1998

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Introducing: RDF

• Improve on PICS, HTML, and XML

• Machine understandable metadata

• Support structured values

• Support metadata bureaus

• Encourage authenticated metadata

• Base for a variety of descriptions:– cataloging, privacy, accessibility, IPR, ...

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RDF Components

• Formal data model

• Syntax for interchange of data

• Schema Type system (schema model)

• Syntax for machine-understandable schemas

• Query and profile protocols

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RDF Data Model

• Imposes structural constraints on the expression of application data models– for consistent encoding, exchange and

processing of metadata

• Enables resource description communities to define their own semantics

• Provides for structural interoperability

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RDF Data Model

• Directed labeled graphs

• Model elements– Resource– Property– Property value– Statement

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RDF Model Primitives

Resource Value

Property

Statement

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RDF Model Example

page.html

John Smith

John’s Home Page

Creator

Title

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Structured Value

page.html

John’s Home Page

Title

Creator

John Smith js@corp.com

Name Email

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RDF Syntax

• Uses eXtensible Markup Language (XML)

• Highly formalized– graph serialization

• Property Names and Values are always unambiguous

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Basic Example

page.html

John Smith

John’s Home Page

DC:Creator

DC:Title

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Basic RDF Example

<?xml version=“1.0”?><rdf:RDF

xmlns:rdf=“http://www.w3.org/TR/WD-rdf-syntax#”xmlns:dc=“http://purl.org/metadata/dublin_core#”>

<rdf:Description about=“page.html”> <dc:Creator>John Smith</dc:Creator> <dc:Title>John’s Home Page</dc:Title> </rdf:Description>

</rdf:RDF>

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Structured Value Example

page.html

John SmithJohn’s Home Page js@corp.com

dc:Title

dc:Creator

Name Email

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Structured Value Example - 1

<?xml version=“1.0”?>

<RDFxmlns=“http://www.w3.org/TR/WD-rdf-syntax#”xmlns:dc=“http://purl.org/metadata/dublin_core#”xmlns:corp=“http://mycorp.com/corpSchema/”>

. . .

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Structured Value Example - 2. . .

<Description about=“page.html”> <dc:Creator> <Description> <corp:Name>John Smith</corp:Name> <corp:Email>js@corp.com</corp:Email> </Description> </dc:Creator> <dc:Title>John’s Home Page</dc:Title></Description>

</RDF>

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Abbreviations: 1<rdf:RDF>

<rdf:Description about=“page.html”> <dc:Creator> <rdf:Description corp:Name=“John Smith” corp:Email=“js@corp.com” /> </dc:Creator> <dc:Title>John’s Home Page</dc:Title></rdf:Description>

</rdf:RDF>

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Abbreviations: 2<rdf:RDF>

<rdf:Description about=“page.html”> <dc:Creator corp:Name=“John Smith” corp:Email=“js@corp.com” /> <dc:Title>John’s Home Page</dc:Title></rdf:Description>

</rdf:RDF>

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Meta-description

page.htmlCost

$0.15

18-Apr-1999

ValidUntil

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Property Reification

page.htmlCost

$0.15

18-Apr-1999

ValidUntil

ObjectSubject

type

StatementCost

Predicate

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Meta-description Example - 1

<?xml version=“1.0”?>

<RDFxmlns:rdf =“http://www.w3.org/TR/WD-rdf-syntax#”xmlns:corp =“http://mycorp.com/schema/”>

. . .

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Meta-description Example - 2

. . .<rdf:Description about=“page.html” bagID=“D_001”> <corp:Cost>$0.15</corp:Cost></rdf:Description>

<rdf:Description aboutEach=“#D_001”> <corp:ValidUntil>18-Apr-1999</corp:ValidUntil></rdf:Description>

</rdf:RDF>

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Meta-description Example - 3

<rdf:RDF>

<rdf:Description about=“page.html” bagID=“D_001” corp:Cost=“$0.15”/>

<rdf:Description aboutEach=“#D_001” corp:ValidUntil=“18-Apr-1999”/>

</rdf:RDF>

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Summary

• RDF is a general-purpose framework• RDF provides structured, machine-

understandable metadata for the Web• Metadata vocabularies can be developed

without central coordination• RDF Schemas describe the meaning of each

property name• Signed RDF is the basis for trust

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For More Information...

The RDF Model and Syntax specification:

http://www.w3.org/TR/WD-rdf-syntax

RDF Schema Working Draft:

http://www.w3.org/TR/WD-rdf-schema

General information about RDF:

http://www.w3.org/RDF