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UKOLUG - July 19981
Metadata for the WebRDF and the Dublin Core
Andy Powell
UKOLN, University of Bath
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.
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
UKOLUG - July 19983
Outline...
• what is RDF?• model• syntax• metadata schemas
• what is the Dublin Core?• Dublin Core in RDF• some examples• current status of RDF• conclusions
UKOLUG - July 19984
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
UKOLUG - July 19985
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
UKOLUG - July 19986
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
UKOLUG - July 19987
RDF - structured example
• provide structured metadata by replacing simple text value by another node.
http://www.ukoln.ac.uk/metadata/Author
Andy Powell [email protected]
Name Email
UKOLUG - July 19988
RDF - reification
• possible to make statements about properties
• process known as reification
http://somewhere.com/page.htmlCost
£0.05
1998-09
ValidUntil
UKOLUG - July 19989
RDF - serialisation syntax
• 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>
UKOLUG - July 199810
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>
UKOLUG - July 199811
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>
UKOLUG - July 199812
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>
UKOLUG - July 199813
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:
UKOLUG - July 199814
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...
UKOLUG - July 199815
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
UKOLUG - July 199816
RDF - schemas
• RDF Schemas define:• available PropertyTypes within a
particular metadata system• structure• allowable values• semantics
• a Schema Definition Language is currently being defined by the W3C
• namespace URIs may point to schema definitions
UKOLUG - July 199817
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
UKOLUG - July 199818
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)
UKOLUG - July 199819
Dublin Core - elements
• Title • Subject • Description • Creator • Publisher • Contributor • Date • Type
• Format • Identifier • Source • Language • Relation• Coverage • Rights
• 15 element core metadata set
UKOLUG - July 199820
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
UKOLUG - July 199821
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
UKOLUG - July 199822
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>
...
UKOLUG - July 199823
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>
UKOLUG - July 199824
DC in RDF
http://www.ukoln.ac.uk/metadata/The UKOLN
Metadata HomePage
DC:Title
<?xml:namespace ns="http://purl.org/dublin_core/schema/" prefix=”DC"?>
<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>
UKOLUG - July 199825
DC in RDF
http://www.ukoln.ac.uk/metadata/The UKOLN
Metadata HomePage
DC:Title
<?xml:namespace ns="http://www.w3.org/TR/WD-rdf/" prefix=”RDF"?>
<?xml:namespace ns="http://purl.org/dublin_core/schema/" prefix=”DC"?>
<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>
UKOLUG - July 199826
RDF - current status
• Some support for RDF in Mozilla (Netscape source code release)
• RDF toolkits under development• Several RDF editors available, e.g.
• DC-dot, UKOLN• Reggie, DSTC
http://www.ukoln.ac.uk/metadata/dcdot/
http://metadata.net/dstc/
• W3C Syntax and Schema drafts still undergoing development
http://www.w3.org/RDF/
UKOLUG - July 199827
Browser Support for RDF
Mozilla supports site maps in RDF, as well as bookmarks and history lists
See Netscape or HotWired home page for a link to the RDF file.
Trusted 3rd
Party Metadata
Embedded Metadata
e.g. sitemaps
Image from http://purl.oclc.org/net/eric/talks/www7/devday/Image from http://purl.oclc.org/net/eric/talks/www7/devday/
UKOLUG - July 199828
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