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Metadata : an overview XML and Educational Metadata, SBU, London, 10 July 2001

Metadata : an overview XML and Educational Metadata, SBU, London, 10 July 2001. Email p.johnston@ukoln.ac.uk URL http://www.ukoln.ac.uk/. Pete Johnston UKOLN, University of Bath Bath, BA2 7AY. UKOLN is supported by:. Metadata: an overview. What is metadata?

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Metadata : an overview XML and Educational Metadata, SBU, London, 10 July 2001

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  1. Metadata :an overviewXML and Educational Metadata, SBU, London, 10 July 2001 Email p.johnston@ukoln.ac.uk URL http://www.ukoln.ac.uk/ Pete Johnston UKOLN, University of Bath Bath, BA2 7AY UKOLN is supported by:

  2. Metadata: an overview • What is metadata? • An introduction to the Dublin Core • An introduction to XML for metadata • An introduction to RDF • RDF, XML and interoperability XML and Educational Metadata, SBU, London, 10 July 2001

  3. What is metadata? • “Data about data” • “Data associated with objects which relieves their potential users of having to have full advance knowledge of their existence or characteristics. A user might be a program or a person.” • Dempsey and Heery, 1998 • “Machine understandable information about web resources or other things.” • Berners-Lee, 1997 XML and Educational Metadata, SBU, London, 10 July 2001

  4. HTML documents digital images databases books museum objects archival records metadata records collections services physical places people abstract “works” concepts events Resources, objects, things? XML and Educational Metadata, SBU, London, 10 July 2001

  5. What operations? • User wants to • find • identify • select • obtain / use • (based on IFLA Functional Requirements for Bibliographical Record) XML and Educational Metadata, SBU, London, 10 July 2001

  6. What operations? (2) • Owner / manager / provider wants to • describe • classify • link, relate • enable and control access and use • commerce • property rights • content rating • authenticity • privacy • manage • administer • preserve XML and Educational Metadata, SBU, London, 10 July 2001

  7. Metadata in practice • Where is metadata created? • embedded in resource • separate entity linked to/from resource • remote database entry • Where is metadata used? • harvested/aggregated to • central database? • multiple distributed databases? • queried by user • used by software agents in service of user XML and Educational Metadata, SBU, London, 10 July 2001

  8. Metadata for a purpose • Different “flavours” of metadata serve different purposes • Simple, generic vs. rich, specific • Automatic generation vs. human creation • Standards and specifications available… • ...but need to choose appropriatestandard for context XML and Educational Metadata, SBU, London, 10 July 2001

  9. Standards for metadata • Benefit of others’ experience, expertise • Provide basis for good practice • Reflect consensus, so facilitate exchange, access, interoperability • May have support in software tools • Standards for • semantics • syntax • structure XML and Educational Metadata, SBU, London, 10 July 2001

  10. Introducing the Dublin Core • Initiative to improve resource discovery on Web • not for complex resource description • simple “document-like objects” • extended to other classes of resource • Interdisciplinary consensus on simple element set • 15 elements • all optional • all repeatable XML and Educational Metadata, SBU, London, 10 July 2001

  11. Introducing the Dublin Core • Provides basic semantic interoperability • across domains • across language communities • may disclose rich description in simple, commonly understood form • Allows for extensibility • but tension between extending DC and choosing other, richer schema XML and Educational Metadata, SBU, London, 10 July 2001

  12. Introducing the Dublin Core • Simplicity of semantics, ease of use • Requires clarity about what resource is being described • e.g. work, expression, manifestation, item • Real resources more complex than (stable) “document-like object”? • characteristics of resources change through time • agents perform actions which produce changes XML and Educational Metadata, SBU, London, 10 July 2001

  13. Introducing XML • Extensible Markup Language • Recommendation of W3C, 1998, 2000 • Defines means of describing tree-structured data in text-based format • Subset of SGML • embedded markup delimits and describes data • Platform-independent syntax • Support for validation against structural model (DTD, XML Schema) XML and Educational Metadata, SBU, London, 10 July 2001

  14. Introducing XML (2) • Initially addressing HTML’s limitations for describing document structure • Now widely adopted syntax for transferring data between programs, systems • Standard programming interfaces • reusable software components • Support from major software vendors • Foundation for “Web services” • distributed applications invoked over Web XML and Educational Metadata, SBU, London, 10 July 2001

  15. Introducing XML (3) • “XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean.” • Berners-Lee, 2001 XML and Educational Metadata, SBU, London, 10 July 2001

  16. Introducing RDF • Resource Description Framework Model & Syntax • Recommendation of W3C, 1999 • Generic “architecture” for metadata • set of conventions for applications exchanging metadata • allow semantics to be defined by different resource description communities • accommodate mixing of metadata from diverse sources XML and Educational Metadata, SBU, London, 10 July 2001

  17. Introducing RDF (2) • Defines • model for making statements about resources • conventions for encoding statements using XML syntax • Object types • Resource : any object identified by URI • not necessarily accessible via Web • Property : attribute to describe resource • properties also uniquely identified by URI • Statement : triple of specific resource, named property, and value XML and Educational Metadata, SBU, London, 10 July 2001

  18. The RDF model • A resource has some property whose value is either (i) a simple string value (literal)…. http:/my.domain/doc/ author Pete • The resource identified by the URI http://my.domain/doc/ has a property “author” whose value is “Pete” • Or, “Pete” is the “author” of the resource identified by http://my.domain/doc/ XML and Educational Metadata, SBU, London, 10 July 2001

  19. The RDF model (2) • … or (ii) another resource http://my.domain/doc/ author name email Pete pete@my.domain • The value of property “author” is another resource which has a property “name” with value “Pete” and a property “email” with value “pete@my.domain” XML and Educational Metadata, SBU, London, 10 July 2001

  20. The RDF XML syntax • XML representation of model • store/exchange descriptions • Property names made unique through use of XML namespaces. • Variant syntaxes <rdf:RDF xmlns:uc=“http://www.ukoln.ac.uk/core/”> <rdf:Description about=”http://my.domain/doc/”> <uc:author>Pete</uc:author> </rdf:Description> </rdf:RDF> XML and Educational Metadata, SBU, London, 10 July 2001

  21. The power of RDF • Extensible model • Supports arbitrary complexity of description • URIs as unique fixed points to identify • resources • properties • Descriptions created independently can be “merged” using URIs as “anchors” XML and Educational Metadata, SBU, London, 10 July 2001

  22. RDF Schema • Resource Description Framework Schema • Candidate Recommendation of W3C, 2000 • Provides mechanisms to define vocabularies used in RDF statements • e.g. Dublin Core metadata element set defined using RDF(S) XML and Educational Metadata, SBU, London, 10 July 2001

  23. RDF Schema (2) • Defines type system • resources grouped into classes • classes related hierarchically (subClassOf) • properties related hierarchically (subPropertyOf) • use of properties constrained (domain, range) • RDF Schema employs RDF model • expressible using RDF/XML syntax XML and Educational Metadata, SBU, London, 10 July 2001

  24. RDF, XML & interoperability • Why isn’t XML enough? • simple statement could be expressed in XML in many different ways • human reader makes interpretation/guess • application program requires prior knowledge of schema/DTD design • RDF imposes extra syntactic constraints on how statement expressed • with RDF/XML, both human and program can interpret description consistently • Less flexibility, greater interoperability XML and Educational Metadata, SBU, London, 10 July 2001

  25. RDF, XML & interoperability • Use XML for exchange when • applications both “know” semantics conveyed by structure of (meta)data • Use RDF/XML for exchange when • (meta)data potentially used by applications without prior “knowledge” of specific schema • (meta)data incorporates overlapping structures from different domains XML and Educational Metadata, SBU, London, 10 July 2001

  26. The Semantic Web • Project of W3C • Present: info on Web for human reader, navigated by simple link • Future: data processed by programs designed independently of data • Requires machine-readable statements about resources and their relationships • using common model • using vocabulary terms tied to unique definitions • definitions available to programs XML and Educational Metadata, SBU, London, 10 July 2001

  27. The Semantic Web (2) • Vision • software agents navigating web of descriptions and “ontologies” (including unknown vocabularies) • making inferences about data collected • communicating via partial understanding • But… • A vision (only?) • Mistrust of the “hype”? • XML (Schema) vs. RDF (Schema)? • Doubts about RDF from KR community? XML and Educational Metadata, SBU, London, 10 July 2001

  28. Conclusions • Meaningful discussion of interoperability requires scope, context • Syntactic interoperability - XML • Structural interoperability - RDF • Semantic interoperability • adoption of standard schema • terminological control • access to RDFS representation of schema XML and Educational Metadata, SBU, London, 10 July 2001

  29. Acknowledgements / further reading • UKOLN metadata pages:http://www.ukoln.ac.uk/metadata/ • Dublin Core Metadata Initiative:http://dublincore.org/ • IFLA, Functional Requirements for Bibliographic Recordhttp://www.ifla.org/VII/s13/frbr/frbr.htm • W3C RDF : http://www.w3.org/RDF/ • W3C Semantic Web :http://www.w3.org/2001/sw/ XML and Educational Metadata, SBU, London, 10 July 2001

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