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XML and “meta-tagging” Technical seminar for Pathfinder LEAs, BECTa, Coventry, 26 February 2002

XML and “meta-tagging” Technical seminar for Pathfinder LEAs, BECTa, Coventry, 26 February 2002. 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:. XML and “meta-tagging”.

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XML and “meta-tagging” Technical seminar for Pathfinder LEAs, BECTa, Coventry, 26 February 2002

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  1. XML and “meta-tagging”Technical seminar for Pathfinder LEAs, BECTa, Coventry, 26 February 2002 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. XML and “meta-tagging” • What is metadata & what is it used for? • Sharing metadata • semantics : introducing the Dublin Core • syntax : introducing the Extensible Markup Language (XML) • structure : the limits of XML • Introducing the Resource Description Framework (RDF) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  3. What is metadata? • “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 • Structured data about resources that can be used to help support a wide range of operations XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  4. HTML documents digital images databases books museum objects archival records metadata records Web sites collections services physical places people abstract “works” concepts events What resources, objects, things? XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  5. Who/what is metadata for? • Used by • human agents (owner, user/researcher, 3rd party services) • software agents (e.g. aggregators, portals, brokers) • Different “flavours” of metadata serve different purposes • simple, generic vs. rich, specific • published widely vs. shared within community vs. used by resource owner/manager • Created by • software tools (resource creation tools, indexing robots/web crawlers) • human agents (resource creator/owner, other parties) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  6. Creator = J Smith Date = 2001-11-05 Title = Report Resource1 Metadata embedded in resource e.g. meta elements in HTML docs; summary properties in word processor docs Can resource support embedding of metadata? Does metadata creator have write access to resource? Can service extract embedded metadata? Metadata about aggregates of resources? Metadata about people, places, concepts? XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  7. Creator = J Smith Date = 2001-11-05 Title = Report Metadata rec 1 Metadata rec = 1 Resource1 Metadata linked from resource e.g. link elements in HTML docs Metadata record may be remote from resource Can resource support embedding of link? Does metadata creator have write access to resource? Can service follow link to metadata record? Metadata about aggregates of resources? Metadata about people, places, concepts? XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  8. Doc = 1 Creator = J Smith Date = 2001-11-05 Title = Report Metadata rec 1 Resource1 Metadata points to resource e.g. most metadata records… Metadata record may be remote from resource Does not require embedding of metadata or link Does not require metadata creator to have write access to resource Service obtains metadata record independently of resource Metadata record can describe anything (with identifier…) Metadata record may persist after resource deleted XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  9. Metadata managed in database Doc Creator Date Title 1 J Smith 2001-11-05 Report Metadata content stored in database, exposed in form(s) appropriate for service(s) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  10. What operations? XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  11. Web site Metadata Single resource provider Resources Resource owner = Metadata creator = Service provider XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  12. Portal Web site Web site Metadata Metadata Web site Multiple resource owners/Metadata creators/Local service providers Separate portal service provider Multiple resource providers XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  13. Portal Web site Web site Metadata Metadata Web site Metadata Web site Multiple resource owners/Metadata creators/Local service providers Other metadata creators Separate portal service provider XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  14. Portal A Web site Web site Metadata Metadata Web site Portal B Web site Web site Metadata XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  15. Metadata for resource discovery • Metadata for resource discovery • is used beyond its creator community • is combined/compared with metadata from other communities • is aggregated or cross-searched by services • Challenges of “interoperability” • How does a metadata provider make metadata records available in a commonly understood form? • (How does a service provider obtain these metadata records from data providers?) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  16. How is metadata shared? • Metadata as language; metadata records as sets of statements • Effective transmission of information requires agreement on • semantics • what terms mean • e.g. “cat”, “to sit”, “mat” • structure • significance of arrangement of terms • e.g. sentence: subject -> verb -> object (in English….) • syntax • rules of expression • “The cat sat on the mat.” XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  17. Sharing metadata : semanticsIntroducing the Dublin Core

  18. 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 "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  19. Title Subject Description Creator Publisher Contributor Date Type Format Identifier Source Language Relation Coverage Rights Introducing the Dublin Core (2) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  20. Introducing the Dublin Core (3) • Simplicity of semantics, ease of use • Provides basic semantic interoperability • across domains • across language communities • Allows for extensibility • but tension between extending DC and choosing other, richer schema • Interoperability requires • use of content rules/standards • clarity about resource being described • e.g. digital surrogate v physical “original” XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  21. Using the Dublin Core • Not a replacement for richer descriptive standards • A “pidgin” language for use by “tourists on the Internet commons” • Tom Baker, “A Grammar of Dublin Core” • Can provide 15 “windows” into richer resource descriptions • disclose rich description in simple form • semantic cross-walks, mappings • (if you have rich descriptions, then) export rather than create? XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  22. Sharing metadata : syntaxIntroducing XML

  23. Introducing XML • Extensible Markup Language • Recommendation of W3C, 1998, 2000 • Defines means of describing tree-structured data in text-based format • embedded markup delimits and describes data • “Meta-language” • language for describing markup languages • can define unlimited number of markup languages • Widely adopted for transferring data between programs, systems XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  24. Introducing XML (2) • Simple syntax • Rules of XML made public so any programmer can write parser • Many parsers available for application developer • reusable software components • standard programming interfaces • Data independent of platform • Support from major software vendors • use of XML increasingly invisible to user • Foundation for “Web services” • distributed applications invoked over Web XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  25. table record record creator date doc title J Smith 2001-11-05 1 Report Doc Creator Date Title 1 J Smith 2001-11-05 Report <table> <record> <doc>1</doc> <creator>J Smith</text> <date>2001-11-05</date> <title>Report</title> </record> </table> XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  26. Doc Creator Date Title Serialisation <record> ... </record> Transmission <record> ... </record> Remote application De-serialisation XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  27. XML : document types & vocabularies • “XML lets me make up names for element types! Great!” • But…. • XML says nothing about what your names mean • will a human recipient of your document recognise your <level> element? • will a software agent process your <level> element correctly? • Communication requires consensus on • structural model of class of document/data • labelling of components • semantics of components • Shared use of common XML “vocabularies” XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  28. XML : DTDs, XML Schemas • Means to codify syntax rules of vocabulary • what markup is allowed • structural constraints on use of markup • N.B. say nothing about what markup means • Document Type Definition • part of XML Recommendation • W3C XML Schema • recent W3C recommendation • data-typing i.e. tighter control on element content • support for combining vocabularies • uses XML syntax • Parser/authoring tool can validate markup of instance against rules in DTD or Schema XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  29. XML : namespaces • Applications wish to use element from multiple vocabularies (DTDs/Schemas) • particularly true of metadata applications • problems of “name collisions” • XML Namespaces • recommendation of W3C • provides universal naming mechanism • Namespace • a collection of names • given a name, which has the form of a URI • Element type names, attribute names qualified by a namespace name (a URI) • through use of prefix XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  30. Sharing metadata : structure The limits of XML

  31. The problem with XML • Statement • this resource (song, document, picture... etc!) has dc:creator “Don Van Vliet” • Multiple expressions in XML <song id=“123”> <title>Frownland</title> <creator>Don Van Vliet</creator> </song> <lyric id=“456” title=“Frownland”> <creator name=“Don Van Vliet”/> </lyric> <music id=“789” creator=“Don Van Vliet”> <title text=“Frownland”/> </music> XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  32. The problem with XML (2) • Different communities make different design choices for DTDs/XML Schemas • all “good” (and valid) • human reader of document can interpret (maybe) • program needs prior “knowledge” of structural conventions in each XML schema • Within resource description community, meaning(s) of structure(s) may be limited • Across communities, potentially unlimited • not scalable in an “open” environment • how to manage ever increasing set of conventions • always encountering unknown schemas XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  33. The problem with XML (3) • “XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean.” • Berners-Lee, 2001 • Consensus on syntax • use of XML • Consensus on semantics of terms • meaning of (uniquely named through XML namespace) elements/attributes • No consensus on meaning of structure • e.g. parent-child element relations XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  34. 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 "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  35. Introducing RDF (2) • Defines • model for making statements about resources • conventions for encoding statements using XML syntax • 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 "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  36. The RDF model • A resource has some property whose value is either (i) a simple string value (literal)… http://js.org/doc/1 author John • The resource identified by the URI http://js.org/doc/1 has a property “author” whose value is “John” • Or, “John” is the “author” of the resource identified by http://js.org/doc/1 XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  37. The RDF model (2) • … or (ii) another resource... http://js.org/doc/1 author name email John john@js.org • The value of property “author” is another resource which has a property “name” with value “John” and a property “email” with value “john@js.org” XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  38. The RDF model (3) • … which may itself have a URI author http://js.org/doc/1 http://js.org/person/john name email John john@js.org XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  39. The power of the RDF model • Extensible model • supports any vocabularies • Supports arbitrary complexity of description • URIs as unique fixed points to identify • resources • properties • Descriptions created independently can be “merged” using URIs as “anchors” • i.e. supports distributed metadata XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  40. First source author http://js.org/doc/1 http://js.org/person/john name email John john@js.org XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  41. Second source http://js.org/doc/1 subject XML XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  42. Third source organisation http://js.org/person/john JS Foundation XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  43. XML JS Foundation subject organisation author http://js.org/doc/1 http://js.org/doc/1 http://js.org/person/john http://js.org/person/john name email John john@js.org Three descriptions merged XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  44. The RDF XML syntax • XML representation of model • to store/exchange descriptions • All property names made unique through use of XML namespaces • Conventions for the meaning of structures in XML document • Service can “know in advance” the meaning of structures • even if unanticipated vocabularies used • “partial understanding” • can read multiple descriptions into store and “merge” on URIs • Generated by tools…. more later! XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  45. RDF Schema • Resource Description Framework Schema • Candidate Recommendation of W3C, 2000 • Provides mechanisms to describe • terms used in RDF statements • semantic relationships between terms • e.g. Dublin Core metadata element set defined using RDF(S) • Defines type system • resources grouped into classes • classes related hierarchically (subClassOf) • properties related hierarchically (subPropertyOf) • use of properties constrained (domain, range) XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  46. RDF Schema (2) • RDF Schema employs RDF model • expressible using RDF/XML syntax • Other “ontology languages” building on RDF/RDFS • e.g. DAML-OIL • describe more complex relations between entities • Berners-Lee’s vision of “Semantic Web” • software agents navigating web of machine-processable descriptions and “ontologies” • making inferences about data collected • communicating via “partial understanding” XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  47. Summary • Resource discovery metadata is shared across boundaries of domain, sector etc • Effective sharing requires consensus on • semantics : shared vocabularies of uniquely named terms • syntax : XML • structure : common XML DTD/schema or RDF? • Simple RDF model as basis of “machine-processable” statements about resources XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

  48. Acknowledgements • UKOLN is funded by Resource: the Council for Museums, Archives and Libraries, the Joint Information Systems Committee (JISC) of the UK higher and further education funding councils, as well as by project funding from the JISC and the European Union. UKOLN also receives support from the University of Bath where it is based. • http://www.ukoln.ac.uk/ XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 2002

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