An Introduction to RDF:

1
An Introduction to RDF

• The Resource Description Framework
• Ian GRAHAM
• Centre for Academic Technology
• Tel [phone]
• 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 [phone]
• Email ltian.graham_at_utoronto.cagt
• Talk http//www.utoronto.ca/ian/talks/