RDF and Metadata

1
RDF and Metadata

• Andy Powell
• UKOLN, University of Bath
• a.powell_at_ukoln.ac.uk
• http//www.ukoln.ac.uk/

UKOLN is funded by the Library and Information
Commission, the Joint Information Systems
Committee 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 University of Bath where it is
based.
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Metadata applications

• resource discovery
• site-maps
• content rating
• e-commerce, rights management
• collaboration
• privacy
• Web-site management

W3Cs Resource Description Framework (RDF)
provides a generic metadata architecture
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Presentation outline...

• what is RDF?
• model
• syntax
• metadata schemas
• what is the Dublin Core?
• Dublin Core in RDF
• some examples
• current status of RDF
• conclusions

4
What is metadata?

• data about data?
• information about resources?
• structured information about stuff
• stuff includes Web resources, books, museum
  artifacts, CDs, abstract works, pieces of
  music
• machine readable
• supports variety of usage scenarios

5
What is RDF?

• Resource Description Framework
• Input from various communities
• Platform for Internet Content Selection (PICS)
• Web Collections (Site maps, MCF)
• Libraries, museums, archives (DC)
• Privacy (P3P)
• W3C Metadata Activity
• Model and Syntax WG
• Schema WG
• Interoperability of metadata
• semantics, structure, syntax

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RDF - the model
resource
property
value
statement

• simple triple-based model
• arc-node diagrams
• resources represented by nodes with URI
• property is some attribute of the resource
• value can be literal or further statement(s)
• a collection of statements about a resource forms
  a description

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RDF - simple example
http//www.ukoln.ac.uk/metadata/
author
Andy Powell

• or, in plain English
• Andy Powell is the author of the resource
  identified by http//www.ukoln.ac.uk/metadata/

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RDF - structured example
http//www.ukoln.ac.uk/metadata/
author
name
emailAddress
Andy Powell
a.powell_at_ukoln.ac.uk

• provide structured metadata by replacing simple
  text value by another node.

9
RDF - reification
http//somewhere.com/page.html
cost
0.05
validUntil
1999-09

• possible to make statements about statements
• process known as reification

10
RDF - serialisation syntax
http//www.ukoln.ac.uk/metadata/
title
The UKOLN Metadata Home Page
ltrdfRDFgt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
lttitlegtThe UKOLN Metadata Home Pagelt/titlegt
lt/rdfDescriptiongt lt/rdfRDFgt

• 2 XML serialisation syntaxes
• allows us to write down the RDF model in a way
  that can be processed by machines

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RDF - serialisation syntax
http//www.ukoln.ac.uk/metadata/
title
The UKOLN Metadata Home Page
ltrdfRDFgt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
lttitlegtThe UKOLN Metadata Home Pagelt/titlegt
lt/rdfDescriptiongt lt/rdfRDFgt
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RDF - serialisation syntax
http//www.ukoln.ac.uk/metadata/
title
The UKOLN Metadata Home Page
ltrdfRDFgt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
lttitlegtThe UKOLN Metadata Home Pagelt/titlegt
lt/rdfDescriptiongt lt/rdfRDFgt
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RDF - serialisation syntax
http//www.ukoln.ac.uk/metadata/
title
The UKOLN Metadata Home Page
ltrdfRDFgt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
lttitlegtThe UKOLN Metadata Home Pagelt/titlegt
lt/rdfDescriptiongt lt/rdfRDFgt
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RDF - multiple properties
Here is an example of a description with multiple
properties
ltrdfRDFgt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
lttitlegtThe UKOLN Metadata Home Pagelt/titlegt
ltkeywordsgtDublin Core, MARC, TEI, IAFA,
lt/keywordsgt ltdescriptiongt Start of
several Web pages about metadata
lt/descriptiongt lt/rdfDescriptiongt lt/rdfRDFgt
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RDF - review
So, weve looked at simple arc-node diagrams and
serialisation in XML but...

• what does title mean?
• is your title the same as my title?

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RDF - namespaces

• XML namespaces are used to uniquely
• identify each RDF property
• namespaces prefix the property
• separated by , e.g.
• ltukolntitlegtsome titlelt/ukolntitlegt
• each namespace has URI associated with it to
  ensure uniqueness

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RDF - schemas

• RDF Schemas define
• available properties within a particular metadata
  system
• structure
• allowable values
• semantics
• relationships between different schemas
• an RDF Schema Specification is currently being
  finalised by the W3C
• namespace URIs may point to schema definitions

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What is the Dublin Core?

• 15 element metadata set
• primarily resource discovery
• primarily Web-based document-like objects
• emphasis on semantics
• widespread consensus
• several syntaxes currently
• early example of an RDF schema

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DC history...

• workshop series - DC-1 to DC-5
• email discussion list
• DC Policy Advisory Committee
• DC Technical Advisory Committee
• series of RFCs in preparation
• submission to NISO (ISO)

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Dublin Core - elements

• 15 element core metadata set

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

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

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Qualified DC

• DC semantics are defined very broadly.
• Possible to
• refine the meaning of elements using type
• Relation TYPEIsPartOf
• associate value with externally defined scheme
• Subject SCHEMELCSH
• Date SCHEMEISO8601
• indicate language of value
• Title LANGUAGEen

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How is DC currently used?

• Embedded into HTML Web pages
• ltMETAgt tag
• limited functionality
• no structure
• HTML version 4.0 support for SCHEME and LANG
• syntax for qualified DC in ltMETAgt tags not well
  established

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DC in HTML

• ltHTMLgtltHEADgt
• ltTITLEgtUKOLN Home Pagelt/TITLEgt
• ltMETA NAME"DC.Title CONTENT"UKOLN UK Office
  for Library and Information Networking"gt
• ltMETA NAME"DC.Subject" CONTENT"national centre,
  network information support, library community,
  awareness, research, information services, public
  library networking, bibliographic management,
  distributed library systems, metadata, resource
  discovery, conferences, lectures, workshops"gt
• ltMETA NAME"DC.Description" CONTENT"UKOLN is a
  national centre for support in network
  information management in the library and
  information communities. It provides awareness,
  research and information services"gt
• ltMETA NAME"DC.Creator" CONTENTUKOLN
  Information Services Group"gt
• lt/HEADgt
• ...

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DC in RDF
http//www.ukoln.ac.uk/metadata/
The UKOLN Metadata Home Page
dctitle
ltrdfRDF ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
ltdctitlegtThe UKOLN Metadata Home
Pagelt/dctitlegt lt/rdfDescriptiongt lt/rdfRDFgt
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DC in RDF
http//www.ukoln.ac.uk/metadata/
The UKOLN Metadata Home Page
dctitle
ltrdfRDF xmlnsdc"http//purl.org/dc/element
s/1.0/"gt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
ltdctitlegtThe UKOLN Metadata Home
Pagelt/dctitlegt lt/rdfDescriptiongt lt/rdfRDFgt
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DC in RDF
http//www.ukoln.ac.uk/metadata/
The UKOLN Metadata Home Page
dctitle
ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/
22-rdf-syntax-ns" xmlnsdc"http//purl.org/dc/
elements/1.0/"gt ltrdfDescription
abouthttp//www.ukoln.ac.uk/metadata/gt
ltdctitlegtThe UKOLN Metadata Home
Pagelt/dctitlegt lt/rdfDescriptiongt lt/rdfRDFgt
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DC in RDF
http//www.ukoln.ac.uk/metadata/
The UKOLN Metadata Home Page
dctitle
lt?xml version"1.0"?gt ltrdfRDF
xmlnsrdf"http//www.w3.org/1999/02/22-rdf-syntax
-ns" xmlnsdc"http//purl.org/dc/elements/1.0/
"gt ltrdfDescription abouthttp//www.ukoln.
ac.uk/metadata/gt ltdctitlegtThe UKOLN
Metadata Home Pagelt/dctitlegt
lt/rdfDescriptiongt lt/rdfRDFgt
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DC in RDF in HTML !

• cant embed standard RDF/XML syntax because
  content not hidden
• embed using abbreviated syntax
• embed at end of HTML ltHEADgt section
• if this isnt possible ltLINKgt to external RDF
  file, e.g.

ltLINK rel"meta" href"mydocMetadata.dc.rdf"gt
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DC in RDF - abbreviated
http//www.ukoln.ac.uk/metadata/
The UKOLN Metadata Home Page
dctitle
ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/
22-rdf-syntax-ns" xmlnsdc"http//purl.org/dc/
elements/1.0/"gt ltrdfDescription
about"http//www.ukoln.ac.uk/metadata/"
dctitle"The UKOLN Metadata Home Page"
/gt lt/rdfRDFgt
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RDF - current status

• RDF Specification - W3C Recommendation
• RDF Schema Spec - Proposed Recommendation
• Some support for RDF in Mozilla
• RDF toolkits/parsers under development
  http//www.w3.org/RDF/Implementations/SiRPAC/
• Several RDF editors available, e.g.
• DC-dot, UKOLN
• Reggie, DSTC
• http//www.ukoln.ac.uk/metadata/dcdot/
• http//metadata.net/dstc/
• Various other RDF-based services

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Conclusions

• 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
• Dublin Core is one of the key RDF Schemas
• signed RDF is the basis for trust

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Further information

• Resource Description Framework (RDF) Model and
  Syntax Specificationhttp//www.w3.org/TR/REC-rdf-
  syntax/
• Resource Description Framework (RDF) Schema
  Specificationhttp//www.w3.org/TR/PR-rdf-schema/
• Dublin Corehttp//purl.org/dc/
• DC-Datamodel homehttp//www.mailbase.ac.uk/lists/
  dc-datamodel/
• INDECShttp//www.indecs.org/
• DC-dothttp//www.ukoln.ac.uk/metadata/dc-dot/
• Reggiehttp//metadata.net
• SiRPAChttp//www.w3.org/RDF/Implementations/SiRPA
  C/http//www.ukoln.ac.uk/metadata/resources/rdf/p
  arser/
• Representing vCard v3.0 in RDFhttp//www.dstc.edu
  .au/RDU/RDF/draft-iannella-vcard-rdf-00.txt