XML and “meta-tagging” Technical seminar for Pathfinder LEAs, BECTa, Coventry, 26 February 2002 Pete Johnston UKOLN, University of Bath Bath, BA2 7AY UKOLN is supported by: URL

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

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 Metadata embedded in resource Resource1 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? Creator = J Smith Date = Title = Report

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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? Resource1 Metadata rec 1 Metadata rec = 1 Creator = J Smith Date = Title = Report

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 Resource1 Metadata rec 1 Creator = J Smith Date = Title = Report Doc = 1

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb Metadata managed in database J Smith Report CreatorDateTitleDoc 1 Metadata content stored in database, exposed in form(s) appropriate for service(s)

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb What operations? Owner / manager / provider establish control of own resources; administer/manage (through time); disclose/promote own resources widely; enable and control access/use; contextualise Other metadata creator disclose/promote resources (including resources owned by others); re-contextualise (re-describe, annotate) Discovery service disclose/promote resources from range of providers; re-contextualise (re-describe, annotate); facilitate user discovery End user find, identify, select resources from range of providers; obtain/use; interpret

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

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

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

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 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.”

Sharing metadata : semantics Introducing the Dublin Core

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

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 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?

Sharing metadata : syntax Introducing XML

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 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 J Smith Report J Smith Report CreatorDateTitleDoc 1 record title Report creator J Smith date table record doc 1

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb CreatorDateTitleDoc Serialisation Transmission De-serialisation Remote application

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 element? –will a software agent process your 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 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 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

Sharing metadata : structure The limits of XML

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb The problem with XML Statement –this resource (song, document, picture... etc!) has dc:creator “Don Van Vliet” Multiple expressions in XML Frownland Don Van Vliet

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 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 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 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 The RDF model author John A resource has some property whose value is either (i) a simple string value (literal)… –The resource identified by the URI has a property “author” whose value is “John” –Or, “John” is the “author” of the resource identified by

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb The RDF model (2) … or (ii) another resource... author name –The value of property “author” is another resource which has a property “name” with value “John” and a property “ ” with value

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb The RDF model (3) … which may itself have a URI author John name

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 First source author John name

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb Second source subject XML

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb Third source organisation JS Foundation

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb author John name organisation JS Foundation subject XML Three descriptions merged

XML and "meta-tagging", BECTa Pathfinders, Coventry, 26 Feb 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 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 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 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 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.