Metadata for the Web RDF and the Dublin
Metadata for the Web RDF 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. 1
Metadata applications • • resource discovery site-maps content rating e-commerce, rights management collaboration privacy Web-site management W 3 C’s Resource Description Framework (RDF) provides a generic metadata architecture 2 UKOLUG - July 1998
Outline. . . • what is RDF? • model • syntax • metadata schemas • what is the Dublin Core? • Dublin Core in RDF • some examples • current status of RDF • conclusions 3 UKOLUG - July 1998
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 (P 3 P) W 3 C Metadata Activity • Model and Syntax WG • Schema WG Interoperability of metadata • semantics, structure, syntax 4 UKOLUG - July 1998
RDF - the model Property. Type Value Resource Property • based on mathematical model • arc-node diagrams • Web resources represented by nodes with URI • collections of properties known as ‘descriptions’ 5 UKOLUG - July 1998
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/” 6 UKOLUG - July 1998
RDF - structured example http: //www. ukoln. ac. uk/metadata/ Author Name Andy Powell Email a. powell@ukoln. ac. uk • provide structured metadata by replacing simple text value by another node. 7 UKOLUG - July 1998
RDF - reification http: //somewhere. com/page. html Cost £ 0. 05 Valid. Until 1998 -09 • possible to make statements about properties • process known as reification 8 UKOLUG - July 1998
RDF - serialisation syntax http: //www. ukoln. ac. uk/metadata/ 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> • serialisation syntax based on XML • allows us to write down the RDF model in a way that can be processed by machines 9 UKOLUG - July 1998
RDF - serialisation syntax http: //www. ukoln. ac. uk/metadata/ 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> 10 UKOLUG - July 1998
RDF - serialisation syntax http: //www. ukoln. ac. uk/metadata/ 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> 11 UKOLUG - July 1998
RDF - serialisation syntax http: //www. ukoln. ac. uk/metadata/ 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> 12 UKOLUG - July 1998
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: RDF> 13 UKOLUG - July 1998
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’? 14 UKOLUG - July 1998
RDF - namespaces XML namespaces are used to uniquely identify each Property. Type • namespaces prefix the Property. Type • separated by ‘: ’, e. g. <UKOLN: Title>some title</UKOLN: Title> • each namespace has URI associated with it to ensure uniqueness 15 UKOLUG - July 1998
RDF - schemas • RDF Schemas define: • available Property. Types within a particular metadata system • structure • allowable values • semantics • a Schema Definition Language is currently being defined by the W 3 C • namespace URIs may point to schema definitions 16 UKOLUG - July 1998
What is the Dublin Core? • • 17 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
DC history. . . • • • 18 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
Dublin Core - elements • 15 element core metadata set • • 19 Title Subject Description Creator Publisher Contributor Date Type • • Format Identifier Source Language Relation Coverage Rights UKOLUG - July 1998
Qualified DC DC semantics are defined very broadly. Possible to: • refine the meaning of elements using ‘type’: • Relation TYPE=Is. Part. Of • associate value with externally defined ‘scheme’: • Subject SCHEME=LCSH • Date SCHEME=ISO 8601 • indicate ‘language’ of value • Title LANGUAGE=en 20 UKOLUG - July 1998
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 21 UKOLUG - July 1998
DC in HTML 22 <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
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> 23 UKOLUG - July 1998
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> 24 UKOLUG - July 1998
DC in RDF http: //www. ukoln. ac. uk/metadata/ DC: Title The UKOLN Metadata Home Page <? xml: namespace ns="http: //www. w 3. 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> 25 UKOLUG - July 1998
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/ • W 3 C Syntax and Schema drafts still undergoing development http: //www. w 3. org/RDF/ 26 UKOLUG - July 1998
Browser Support for RDF Mozilla supports site Trusted 3 rd maps in RDF, as well Party Metadata as bookmarks and history lists See Netscape or Hot. Wired home page for a link to the RDF file. Embedded Metadata e. g. sitemaps Image from http: //purl. oclc. org/net/eric/talks/www 7/devday/ 27 UKOLUG - July 1998
Conclusions · RDF is a general-purpose framework · RDF provides structured, machineunderstandable 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 28 UKOLUG - July 1998
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