UKOLUG - July 1998 1 Metadata for the Web RDF and the Dublin Core Andy Powell UKOLN, University of Bath [email protected]http://www.ukoln.ac.uk/ UKOLN is funded by the British Library Research and Innovation Centre, the Joint Information Systems Committee of the Higher Education Funding Councils, as well as by project funding from the JISC’s Electronic Libraries Programme and the European Union. UKOLN also receives support from the University of Bath where it is based.
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UKOLUG - July 1998 1 Metadata for the Web RDF and the Dublin Core Andy Powell UKOLN, University of Bath [email protected] UKOLN.
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UKOLN is funded by the British Library Research and Innovation Centre, the Joint Information Systems Committee of the Higher Education Funding
Councils, as well as by project funding from the JISC’s Electronic Libraries Programme and the European Union.
UKOLN also receives support from the University of Bath where it is based.
UKOLUG - July 19982
Metadata applications
•resource discovery•site-maps•content rating•e-commerce, rights management•collaboration•privacy•Web-site management
W3C’s Resource Description Framework (RDF) provides a generic metadata architecture
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Outline...
• what is RDF?• model• syntax• metadata schemas
• what is the Dublin Core?• Dublin Core in RDF• some examples• current status of RDF• conclusions
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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
• based on mathematical model• arc-node diagrams• Web resources represented by nodes with
URI• collections of properties known as
‘descriptions’
ResourcePropertyType
Value
Property
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RDF - simple example
• or, in plain English…
“Andy Powell is the author of the resource identified by http://www.ukoln.ac.uk/metadata/”
http://www.ukoln.ac.uk/metadata/Author
Andy Powell
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RDF - structured example
• provide structured metadata by replacing simple text value by another node.
• serialisation syntax based on XML• allows us to write down the RDF model in
a way that can be processed by machines
http://www.ukoln.ac.uk/metadata/Title The UKOLN
Metadata HomePage
Title
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <Title>The UKOLN Metadata Home Page</Title> </RDF:Description></RDF:RDF>
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RDF - serialisation syntax
http://www.ukoln.ac.uk/metadata/Title The UKOLN
Metadata HomePage
Title
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <Title>The UKOLN Metadata Home Page</Title> </RDF:Description></RDF:RDF>
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RDF - serialisation syntax
http://www.ukoln.ac.uk/metadata/Title The UKOLN
Metadata HomePage
Title
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <Title>The UKOLN Metadata Home Page</Title> </RDF:Description></RDF:RDF>
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RDF - serialisation syntax
http://www.ukoln.ac.uk/metadata/Title The UKOLN
Metadata HomePage
Title
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <Title>The UKOLN Metadata Home Page</Title> </RDF:Description></RDF:RDF>
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RDF - multiple properties
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <Title>The UKOLN Metadata Home Page</Title> <Keywords>Dublin Core, MARC, TEI, IAFA, … </Keywords> <Description> Start of several Web pages about metadata </Description> </RDF:Description></RDF:RDF>
Here is an example of a description with multiple properties:
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RDF - review
•what does ‘Title’ mean?•is your ‘Title’ the same as my ‘Title’?
So, we’ve looked at simple arc-node diagrams and serialisation in XML…
but...
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RDF - namespaces
XML namespaces are used to uniquely
identify each PropertyType• namespaces prefix the PropertyType• separated by ‘:’, e.g.
<UKOLN:Title>some title</UKOLN:Title>
• each namespace has URI associated with it to ensure uniqueness
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RDF - schemas
• RDF Schemas define:• available PropertyTypes within a
• a Schema Definition Language is currently being defined by the W3C
• namespace URIs may point to schema definitions
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What is the Dublin Core?
• 15 element metadata set• resource discovery• Web-based document-like objects• emphasis on semantics• widespread consensus• several syntaxes currently• set to become an 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 5 RFCs in preparation• submission to NISO (…ISO)
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Dublin Core - elements
• Title • Subject • Description • Creator • Publisher • Contributor • Date • Type
• Format • Identifier • Source • Language • Relation• Coverage • Rights
• 15 element core metadata set
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Qualified DC
DC semantics are defined very broadly.
Possible to:• refine the meaning of elements using ‘type’:
• Relation TYPE=IsPartOf• associate value with externally defined ‘scheme’:
• Subject SCHEME=LCSH• Date SCHEME=ISO 8601
• indicate ‘language’ of value• Title LANGUAGE=en
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How is DC currently used?
Embedded into HTML Web pages• <META> tag• limited functionality
• no structure
• version 4.0 support for SCHEMEs• syntax for qualified DC in <META>
tags not well established
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DC in HTML<HTML><HEAD>
<TITLE>UKOLN Home Page</TITLE>
<META NAME="DC.Title” CONTENT="UKOLN: UK Office for Library and Information Networking">
<META 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">
<META 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">
<META NAME="DC.Creator" CONTENT=”UKOLN Information Services Group">
</HEAD>
...
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DC in RDF
http://www.ukoln.ac.uk/metadata/The UKOLN
Metadata HomePage
DC:Title
<RDF:RDF> <RDF:Description RDF:HREF=”http://www.ukoln.ac.uk/metadata/”> <DC:Title>The UKOLN Metadata Home Page</DC:Title> </RDF:Description></RDF:RDF>