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RDF and Dublin Core: Metadata Applications and Syntax Overview

This article provides an overview of RDF (Resource Description Framework) and its use in Dublin Core metadata. It covers the RDF model, syntax, metadata schemas, examples, and the current status of RDF.

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RDF and Dublin Core: Metadata Applications and Syntax Overview

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  1. Metadata for the WebRDF and the Dublin Core Andy Powell UKOLN, University of Bath a.powell@ukoln.ac.uk 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 1998

  2. 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 1998

  3. 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 1998

  4. 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 1998

  5. RDF - the model PropertyType Resource • based on mathematical model • arc-node diagrams • Web resources represented by nodes with URI • collections of properties known as ‘descriptions’ Value Property UKOLUG - July 1998

  6. 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 1998

  7. RDF - structured example • provide structured metadata by replacing simple text value by another node. http://www.ukoln.ac.uk/metadata/ Author Name Email Andy Powell a.powell@ukoln.ac.uk UKOLUG - July 1998

  8. RDF - reification • possible to make statements about properties • process known as reification http://somewhere.com/page.html Cost £0.05 ValidUntil 1998-09 UKOLUG - July 1998

  9. RDF - serialisation syntax http://www.ukoln.ac.uk/metadata/ • serialisation syntax based on XML • allows us to write down the RDF model in a way that can be processed by machines Title Title The UKOLN Metadata Home Page <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 1998

  10. RDF - serialisation syntax http://www.ukoln.ac.uk/metadata/ Title Title The UKOLN Metadata Home Page <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 1998

  11. RDF - serialisation syntax http://www.ukoln.ac.uk/metadata/ Title Title The UKOLN Metadata Home Page <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 1998

  12. RDF - serialisation syntax http://www.ukoln.ac.uk/metadata/ Title Title The UKOLN Metadata Home Page <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 1998

  13. RDF - multiple properties • Here is an example of a description with 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> UKOLUG - July 1998

  14. RDF - review • So, we’ve looked at simple arc-node diagrams and serialisation in XML… • but... • what does ‘Title’ mean? • is your ‘Title’ the same as my ‘Title’? UKOLUG - July 1998

  15. 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 1998

  16. 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 1998

  17. 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 1998

  18. 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 1998

  19. Title Subject Description Creator Publisher Contributor Date Type Format Identifier Source Language Relation Coverage Rights Dublin Core - elements • 15 element core metadata set UKOLUG - July 1998

  20. 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 1998

  21. 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 1998

  22. 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 1998

  23. DC in RDF http://www.ukoln.ac.uk/metadata/ DC:Title The UKOLN Metadata Home Page <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 1998

  24. DC in RDF http://www.ukoln.ac.uk/metadata/ DC:Title The UKOLN Metadata Home Page <?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 1998

  25. DC in RDF http://www.ukoln.ac.uk/metadata/ DC:Title The UKOLN Metadata Home Page <?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 1998

  26. 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 1998

  27. Browser Support for RDF Trusted 3rd Party Metadata • 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. Embedded Metadata e.g. sitemaps Image fromhttp://purl.oclc.org/net/eric/talks/www7/devday/ UKOLUG - July 1998

  28. 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 UKOLUG - July 1998

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