1 Dublin Core and its implementation in RDF/XML Paul Miller Interoperability Focus UK Office for...

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Dublin Core and its implementation in RDF/XML

Paul Miller

Interoperability FocusUK Office for Library & Information Networking (UKOLN)

P.Miller@ukoln.ac.uk http://www.ukoln.ac.uk/

UKOLN is funded by the Library and Information Commission, the Joint Information Systems Committee (JISC) of the Higher Education Funding Councils, as well as by project funding from the JISC and the European Union.

UKOLN also receives support from the Universities of Bath and Hull where staff are based.

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Introducing the Dublin Core

• An attempt to improve resource discovery on the Web

– now adopted more broadly

• Building an interdisciplinary consensus about a core element set for resource discovery

– simple and intuitive– cross–disciplinary — not just libraries!!– international– open and consensual– flexible.

See http://purl.org/dc/See http://purl.org/dc/

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• 15 elements of descriptive metadata• All elements optional• All elements repeatable• The whole is extensible

– offers a starting point for semantically richer descriptions

• Interdisciplinary– libraries, government, museums,

archives…

• International– available in more than 20 languages, with

more on the way...

Introducing the Dublin Core

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• Title• Creator• Subject• Description• Publisher• Contributor• Date• Type

• Format• Identifier• Source• Language• Relation• Coverage• Rights

http://purl.org/dc/

Introducing the Dublin Core

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Introducing XML

• eXtensible Markup Language• World Wide Web Consortium

recommendation• Simplified subset of SGML for use on Web• Addresses HTML’s lack of evolvability• Easily extended• Supported by major vendors• Increasingly used as a transfer syntax, but

capable of far more….

See http://www.w3.org/XML/See http://www.w3.org/XML/

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Introducing RDF

• Resource Description Framework• W3C Recommendation• Improves upon XML, HTML, PICS…• Machine understandable metadata!• XML as syntax• Locally defined semantics• Supports structure• Increasing interest.

See http://www.ukoln.ac.uk/metadata/resources/dc/datamodel/WD–dc–rdf/

See http://www.ukoln.ac.uk/metadata/resources/dc/datamodel/WD–dc–rdf/

See http://www.w3.org/RDF/See http://www.w3.org/RDF/

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Extending DC (semantic)

• Improve descriptive precision by adding sub–structure (subelements and schemes)

– Greater precision = lesser interoperability

• Should ‘dumb down’ gracefully

Creator

First Name

Surname Contact Info

Affiliation

Based on a slide by Stu Weibel

Element qualifier Value qualifier

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Extending DC (modularity)

• Modular extensibility…• Additional elements to support local needs• Complementary packages of metadata

• …but only if we get the building blocks right!

Description Spatial character

Terms & Conditions

Based on a slide by Stu Weibel

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Data Integration• “The author of this document is Paul”• “Paul is the author of this document”• “This document is authored by Paul”• “The author of this document is Paul”

• At least 3 Representation(s) in XML:

<author> <url> http://doc_url </url> <name> Paul </name></author>

<document> <author> <name> Paul </name> </author> <url> http://doc_url </url></document>

<document href = “http://doc_url”author = “Paul”/>

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Data Integration

• Querying XML documents is hard• N ways of mapping XML to logical structure• Requires the normalization of all possible

representations for effective query

• Mean the same thing to a person• Mean very different things to a machine• RDF much less flexible

• less flexible = more interoperable! • consistent way of representing statements.

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RDF Data Model basics

ResourceProperty

ValueResource

Statement

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A simple example

ResourceAuthor

“Paul”

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DC in RDF

• Draft proposal of Dublin Core community’s Data Model working group• Guidance on expressing the Dublin Core

within the Resource Description Framework (RDF)

• http://www.ukoln.ac.uk/metadata/resources/ dc/datamodel/WD-dc-rdf/

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Dublin Core ‘Data Model’

rdf:Valuedc:element

Resource

dcq:elementType(element qualifier)

dcq:elementScheme(value qualifier)

Based on a slide by Stu Weibel

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A simple example

“Created”

dcq:dateType

“1998-11-10”

rdf:Valuedc:date

Resource

“ISO 8601”

dcq:dateScheme

Based on a slide by Stu Weibel

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A simple 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/1.0/"><rdf:Description rdf:about="http://www.ukoln.ac.uk/metadata/resources/dc/

datamodel/WD-dc-rdf/"><dc:title> Guidance on expressing the Dublin Core within the Resource Description

Framework (RDF) </dc:title><dc:creator> Eric Miller </dc:creator><dc:creator> Paul Miller </dc:creator><dc:creator> Dan Brickley </dc:creator><dc:subject> Dublin Core; Resource Description Framework; RDF; eXtensible Markup

Language; XML </dc:subject><dc:publisher> Dublin Core Metadata Initiative </dc:publisher><dc:contributor> Dublin Core Data Model Working Group </dc:contributor><dc:date> 1999-07-01 </dc:date><dc:format> text/html </dc:format><dc:language> en </dc:language></rdf:Description></rdf:RDF>

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A scary example… part 1<?xml version="1.0" encoding="ISO-8859-1"?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:dc="http://purl.org/dc/elements/1.0/" xmlns:dcq="http://purl.org/dc/qualifiers/1.0/">

<rdf:Description rdf:about="http://www.ukoln.ac.uk/metadata/resources/dc/datamodel/ WD-dc-rdf/">

<dc:title> <rdf:Alt> <rdf:li xml:lang="en">Guidance on expressing the Dublin Core

within the Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="no">Veiledning å uttrykke Dublin Core innenfor

rammen av Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="de">Dublin Core in RDF: Eine

Anleitung</rdf:li> </rdf:Alt></dc:title>

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A scary example… part 2!<dc:creator> <rdf:Bag> <rdf:li>Eric Miller</rdf:li> <rdf:li>Paul Miller</rdf:li> <rdf:li>Dan Brickley</rdf:li> </rdf:Bag></dc:creator><dc:description> <rdf:Alt> <rdf:li xml:lang="en">This document describes work carried out

by the Data Model Working Group of the Dublin Core Metadata Initiative…</rdf:li>

<rdf:li xml:lang="no">Dette dokumentet beskriver arbeide utført av arbeidsgruppen for datamodellering knyttet til Dublin Core- initiativet. Spesifikt diskuterer dokumentet hvordan de femten elementene i Dublin Core …</rdf:li>

</rdf:Alt></dc:description>

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A scary example… part 3!!<dc:subject> Dublin Core; Resource Description Framework; RDF;

eXtensible Markup Language; XML </dc:subject><dc:publisher> Dublin Core Metadata Initiative </dc:publisher><dc:contributor> Dublin Core Data Model Working Group

</dc:contributor><dc:date> <rdf:Description> <dcq:dateScheme> WTN8601 </dcq:dateScheme> <rdf:value> 1999-07-01 </rdf:value> </rdf:Description></dc:date><dc:format> <rdf:Description> <dcq:formatScheme> IMT </dcq:formatScheme> <rdf:value> text/html </rdf:value> </rdf:Description></dc:format>

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A scary example… part 4!!!<dc:language> <rdf:Description> <dcq:languageScheme> RFC1766 </dcq:languageScheme> <rdf:value> en </rdf:value> </rdf:Description></dc:language></rdf:Description></rdf:RDF>

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Useful Links• Dublin Core

• http://purl.org/dc/

• RDF• http://www.w3.org/RDF/

• XML• http://www.w3.org/XML/

• DC–Dot• http://www.ukoln.ac.uk/metadata/dcdot/

• SiRPAC• http://www.w3.org/RDF/Implementations/SiRPAC/

• DC Datamodel Document• http://www.ukoln.ac.uk/metadata/resources/

dc/datamodel/WD-dc-rdf/