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An Introduction to RDF:

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To share names, and meanings (shared semantics) Example: Dublin Core Metadata ... LCNA (Library of Congress Name Authority File) Describing Resources. Many ... – PowerPoint PPT presentation

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Title: An Introduction to RDF:


1
An Introduction to RDF
  • The Resource Description Framework
  • Ian GRAHAM
  • Centre for Academic Technology
  • Tel 978-4548
  • Email ltian.graham_at_utoronto.cagt
  • Talk http//www.utoronto.ca/ian/talks/

2
Overview
  • The problems and issues
  • Resources and Metadata
  • Modularizability
  • Example The Dublin Core Set
  • Expression RDF and XML
  • Examples This talk is based on material
    presented at WWW8 by Carl Lagoze, Eric Miller and
    Stu Weibel

3
The Problems
  • Too much Web information
  • around 1,000,000,000 (1?109) resources
  • Many different types of resources
  • text, images, graphics,
  • audio, video, multimedia,
  • databases, Web applications,
  • resource metadata (pointers to media servers)

4
The Problems (cont.)
  • Information not indexable
  • No common scheme for doing so
  • Short-lived, dynamic resources
  • Differing relationships between authors,
    publishers, info intermediaries, users
  • Each community uses their own approach

5
The Problems (cont.)
  • Information not shareable
  • Difficult to share information
  • Difficult to share information about information
  • no common cataloging schemes

6
Talk outline
  • The problems and issues
  • Resources and Metadata
  • Modularizability
  • Example The Dublin Core Set
  • Expression RDF and XML
  • Examples

7
Main Issues
  • Metadata
  • Information about information
  • Structured data about data
  • Many types/forms of metadata, dependent on role

8
Types of Metadata
Web Resource discovery
(Intellectual) property rights management
Document management administration
Archival information / status
Security User authentication
Content ratings (PICS)
Process description control
Product Services Descriptions
Database / data schemas
9
Second Issue
  • Language for expressing metadata.
  • Must be
  • universal (so all can understand)
  • flexible (to incorporate different types)
  • extensible (flexible to custom types)
  • simple (to encourage adoption)
  • modular (so that schemes can be mixed,
    extended)

10
Third Issue
  • Shared Metadata Architectures
  • To share names, and meanings (shared semantics)
  • Example Dublin Core Metadata

11
Example Dublin Core
  • Not a weapons system from Star Trek
  • Simple semantics for describing resources --
    I.e., metadata
  • simple, intuitive,
  • cross-disciplinary, flexible

12
DC Element Set
  • Title
  • Author/creator
  • Subject/keywords
  • Description
  • Publisher
  • Other Contributor
  • Date
  • Resource type
  • Format
  • Resource Identifier
  • Source
  • Language
  • Relation
  • Coverage
  • Rights management

13
Extensibility
  • Substructure to define more detail

Creator
Contact Info
Given name
Phone
Surname
Fax
Affiliation
Email
14
Use of Extensibility
  • DC a high-level framework
  • Describe features common to all resources
  • Extensible to domain-specific schemes
  • Refine semantics of keywords
  • Add special vocabularies for data (e.g., LC), or
    for encodings (e.g., 7/11/99 or 11/7/99)

15
Other Metadata Models
  • Dublin core
  • vCard (business-card data)
  • vCalendar (calendar/scheduling data)
  • LCNA (Library of Congress Name Authority
    File)

16
Describing Resources
  • Many things to describe
  • Need flexible scheme that supports
  • Different metadata schemes
  • at the same time
  • Express in some useful syntax
  • (e.g., XML)

17
Talk Outline
  • The problems and issues
  • Resources and Metadata
  • Modularizability
  • Example The Dublin Core Set
  • Expression RDF and XML
  • Examples

18
RDF
  • Resource Description Framework
  • Machine understandable format
  • Framework for many classes of resource
    descriptions
  • catalog, accessibility, Intellectual property
    rights

19
RDF Components
  • Model for the framework (graphical)
  • Resources
  • Properties
  • Values
  • Statements
  • Containers
  • Syntax for interchange (XML dialect)

20
Simple RDF Example
Resource
Property
Value
http//foo.org/g
dcTitle
RDF talk
dcCreator
Ian Graham
21
Expression as XML
http//foo.org/g
ltRDF xmlnshttp//www.w3.org/TR/
xmlnsdchttp//purl.org/dc/ gt ltDescription
abouthttp//foo.org/ggt ltdcTitlegt RDF Talk
lt/dcTitlegt ltdcCreatorgtIan
Grahamlt/dcCreatorgt lt/Descriptiongt lt/RDFgt
dcTitle
dcCreator
RDF talk
Ian Graham
22
Less Simple RDF Example
http//foo.org/g
dcTitle
RDF talk
dcCreator
me
bibAff
http//utoronto.ca
bibEmail
bibName
ian_at_goo.org
Ian Graham
23
Written in XML as
ltRDF xmlnshttp//www.w3.org/TR/..
xmlnsdchttp//purl.org/dc/
xmlnsbibhttp//www.bibby gt ltDescription
abouthttp//foo.org/g gt ltdcTitlegt RDF Talk
lt/dcTitlegt ltdcCreatorgt ltDescriptiongt
ltbibNamegtIan Graham lt/bibNamegt
ltbibEmailgt ian_at_goo.org lt/bibEmailgt
ltbibAff resourcehttp//utoronto.ca /gt
lt/Descriptiongt lt/dcCreatorgt lt/Descriptiongt lt/R
DFgt
http//foo.org/g
dcTitle
RDF talk
dcCreator
me
http//utoronto.ca
bibAff
bibEmail
bibName
ian_at_goo.org
Ian Graham
24
Other Important Concepts
  • Bags -- groups of things
  • Sequences -- ordered group of things
  • Alternates -- Alternate things/values
  • First value is the default
  • Must be at least one

25
Bags, Sequences
  • Bag index categoriesltcaCategoriesgtltBaggt
    ltligtCategory 1lt/ligt ltligtCat. 2lt/ligt ltligtBleel
    lt/ligt lt/Baggtlt/caCategoriesgt
  • Seq SequenceltcaCategoriesgtltSeqgt
    ltligtCategory 1lt/ligt ltligtCat. 2lt/ligt ltligtBleel
    lt/ligt lt/Seqgtlt/caCategoriesgt

26
Talk Outline
  • The problems and issues
  • Resources and Metadata
  • Modularizability
  • Example The Dublin Core Set
  • Expression RDF and XML
  • Examples

27
Netscape Open Directory
  • http//www.dmoz.org
  • Directory of Web-accessible resources
  • Human-maintained (people add resources
  • Uses RDF to
  • Describe category structure
  • Describe resources in each category

28
ltRDF xmlnsr"http//www.w3.org/TR/RDF/"
xmlnsd"http//purl.org/dc/elements/1.0/"
xmlns"http//directory.mozilla.org/rdf"gt ltT
opic rid"Top"gt lttag catid"1"/gt
ltdTitlegtToplt/dTitlegt ltnarrow
rresource"Top/Arts"/gt .... lt/Topicgt ltTopic
rid"Top/Arts"gt lttag catid"2"/gt
ltdTitlegtArtslt/dTitlegt ltnarrow
rresource"Top/Arts/Books"/gt ... ltnarrow
rresource"Top/Arts/Artists"/gt ltsymbolic
rresource"TypographyTop/Computers/Fonts"/gt lt/To
picgt .... lt/RDFgt
Category Structure
29
ltRDF xmlnsr"http//www.w3.org/TR/RDF/"
xmlnsd"http//purl.org/dc/elements/1.0/"
xmlns"http//directory.mozilla.org/rdf"gt
... ltTopic rid"Top/Arts"gt lttag catid"2"/gt
ltdTitlegtArtslt/dTitlegt ltlink
rresource"http//www3...ca/./file.html"/gt lt/Top
icgt ltExternalPage about"http//wwwca/file
.html"gt ltdTitlegtJohn phillips Blown
glasslt/dTitlegt ltdDescriptiongtA small display
of glass by John Phillipslt/dDescriptiongt lt
/ExternalPagegt ltTopic rid"Top/Computers"gt
lttag catid"4"/gt ltdTitlegtComputerslt/dTitlegt
ltlink rresource"http//www.cs.tcd.ie/FME/"/gt
ltlink rresourcehttp//foo.asdfsa.."/gt lt/Topicgt
lt/RDFgt
Resources
30
2. Netscape Navigator 5
  • Uses RDF to describe data used in browser
  • (mailbox contents, directory contents)
  • As a way of adding dynamic data access

31
ltrdfRDF xmlnsrdf"http//www.w3.org/TR/WD-rd
f-syntax" xmlnssm"http//www.mozilla.org/sm
art-mail/schema"gt ltrdfDescription
about"http//www.mozilla.org/smart-mail/.gt
ltsmmessage id"4025293"gt
ltsmrecipientgtwat_at_netscape.comlt/smrecipientgt
ltsmsendergthelga_at_netcenter.netlt/smsendergt
ltsmreceived-bygtwing.mcom.comlt/smreceived-bygt
ltsmsubjectgtRecipe for Yam
Soup!lt/smsubjectgt ltsmbodygt
http//www.mozilla.org/smart-mail/get-body.cgi?...
lt/smbodygt lt/smmessagegt
ltsmmessage id"4025294"gt ltsmrecipientgt
wat_at_netscape.com lt/smrecipientgt
ltsmsendergtw2_at_pbox.ohio-state.edult/smsendergt
ltsmreceived-bygtx-wing.mcom.comlt/smreceived-by
gt ltsmsubjectgtWe won our ultimate
gamelt/smsubjectgt ltsmbodygt
http//www.mozilla.org/smart-mail/get-body.cgi?...
lt/smbodygt lt/smmessagegt
lt/rdfDescriptiongt lt/rdfRDFgt
Mailbox Entries
32
Some References
  • RDF
  • http//www.w3.org/RDF/ (Overview)
  • http//www.w3.org/Press/1999/RDF-REC (RDF model
    and syntax spec.)
  • http//www.w3.org/TR/PR-rdf-schema/ (RDF schema
    specification)
  • Dublin Core
  • http//purl.org/dc/
  • ftp//ftp.ietf.org/rfc/rfc2413.txt

33
An Introduction to RDF
  • The Resource Description Framework
  • Ian GRAHAM
  • Centre for Academic Technology
  • Tel 978-4548
  • Email ltian.graham_at_utoronto.cagt
  • Talk http//www.utoronto.ca/ian/talks/
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