An Introduction to RDF:

The Resource Description Framework

Ian GRAHAMCentre for Academic TechnologyTel: 978-4548Email: <ian.graham@utoronto.ca>Talk: http://www.utoronto.ca/ian/talks/

Overview

The problems and issuesResources 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

The Problems:

Too much Web information around 1,000,000,000 (1109)

resources Many different types of resources

text, images, graphics,audio, video, multimedia, databases, Web applications, … resource metadata (pointers to media

servers)

The Problems (cont.):

Information not indexable No common “scheme” for doing so Short-lived, dynamic resources Differing relationships between authors,

publishers, info intermediaries, usersEach community uses their own approach

The Problems (cont.):

Information not shareable Difficult to share information Difficult to share information about

informationno common cataloging schemes

Talk outline:

The problems and issuesResources and Metadata

Modularizability Example: The Dublin Core Set

Expression: RDF and XML Examples

Main Issues:

Metadata Information about information Structured data about data

Many types/forms of metadata, dependent on role:

Types of Metadata:

Web Resource discovery

Content ratings (PICS)

Product &ServicesDescriptions

Document management administration

Security & Userauthentication

(Intellectual)property rightsmanagement

Database / data schemas

Archivalinformation /status

Process description &control

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)

Third Issue:

Shared Metadata Architectures: To share names, and meanings (shared

semantics)

Example: Dublin Core Metadata

Example : Dublin Core

Not a weapons system from Star Trek

Simple semantics for describing resources -- I.e., metadata simple, intuitive, cross-disciplinary, flexible

DC Element Set

TitleAuthor/creatorSubject/keywordsDescriptionPublisherOther ContributorDate

Resource typeFormatResource IdentifierSourceLanguageRelationCoverageRights management

CreatorCreator

Extensibility

Substructure to define more detail

Given name

Surname

Affiliation

Contact Info

Phone

Fax

Email

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)

Other Metadata Models

Dublin core vCard (business-card data)vCalendar (calendar/scheduling

data)LCNA (Library of Congress Name

Authority File)

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)

Talk Outline

The problems and issuesResources and Metadata

Modularizability Example: The Dublin Core Set

Expression: RDF and XMLExamples

RDF

Resource Description Framework Machine understandable format Framework for many classes of

resource descriptionscatalog, accessibility, Intellectual property

rights

RDF Components

Model for the framework (graphical): Resources Properties Values Statements Containers

Syntax for interchange (XML dialect)

Simple RDF Example

http://foo.org/g “RDF talk”dc:Title

dc:Creator

“Ian Graham”

Resource Property Value

Expression as XML

http://foo.org/g

“RDF talk”

dc:Title

dc:Creator

“Ian Graham”

<RDF xmlns=“http://www.w3.org/TR/ … ” xmlns:dc=“http://purl.org/dc/…” > <Description about=“http://foo.org/g”> <dc:Title> RDF Talk </dc:Title> <dc:Creator>Ian Graham</dc:Creator> </Description></RDF>

Less Simple RDF Example

http://foo.org/g “RDF talk”

“me”

http://utoronto.ca

dc:Title

dc:Creator

bib:Aff

“Ian Graham” “ian@goo.org”

bib:Name bib:Email

Written in XML as:

<RDF xmlns=“http://www.w3.org/TR/..” xmlns:dc=“http://purl.org/dc/…” xmlns:bib=http://www.bibby…” ><Description about=“http://foo.org/g” > <dc:Title> RDF Talk </dc:Title> <dc:Creator> <Description> <bib:Name>Ian Graham </bib:Name> <bib:Email:> ian@goo.org </bib:Email> <bib:Aff resource=“http://utoronto.ca” /> </Description> </dc:Creator></Description></RDF>

http://foo.org/g “RDF talk”

“me”http://utoronto.ca

dc:Title

dc:Creator

bib:Aff

“Ian Graham” “ian@goo.org”

bib:Name bib:Email

Other Important Concepts

Bags -- groups of thingsSequences -- ordered group of

thingsAlternates -- Alternate

things/values First value is the default Must be at least one

Bags, Sequences

Bag: index categories

<ca:Categories><Bag> <li>Category 1</li> <li>Cat. 2</li> <li>Bleel </li> </Bag></ca:Categories>

Seq: Sequence

<ca:Categories><Seq> <li>Category 1</li> <li>Cat. 2</li> <li>Bleel </li> </Seq></ca:Categories>

Talk Outline

The problems and issuesResources and Metadata

Modularizability Example: The Dublin Core Set

Expression: RDF and XMLExamples

Netscape Open Directory

http://www.dmoz.org Directory of Web-accessible

resources Human-maintained (people add

resourcesUses RDF to:

Describe category structure Describe resources in each category

<RDF xmlns:r="http://www.w3.org/TR/RDF/" xmlns:d="http://purl.org/dc/elements/1.0/" xmlns="http://directory.mozilla.org/rdf"><Topic r:id="Top"> <tag catid="1"/> <d:Title>Top</d:Title> <narrow r:resource="Top/Arts"/> ....</Topic><Topic r:id="Top/Arts"> <tag catid="2"/> <d:Title>Arts</d:Title> <narrow r:resource="Top/Arts/Books"/> ... <narrow r:resource="Top/Arts/Artists"/> <symbolic r:resource="Typography:Top/Computers/Fonts"/></Topic>....</RDF>

CategoryCategoryStructureStructure

<RDF xmlns:r="http://www.w3.org/TR/RDF/" xmlns:d="http://purl.org/dc/elements/1.0/" xmlns="http://directory.mozilla.org/rdf"> ...<Topic r:id="Top/Arts"> <tag catid="2"/> <d:Title>Arts</d:Title> <link r:resource="http://www3...ca/…./file.html"/></Topic><ExternalPage about="http://www…ca/file .html"> <d:Title>John phillips Blown glass</d:Title> <d:Description>A small display of glass by John Phillips</d:Description></ExternalPage><Topic r:id="Top/Computers"> <tag catid="4"/> <d:Title>Computers</d:Title> <link r:resource="http://www.cs.tcd.ie/FME/"/> <link r:resource=”http://foo.asdfsa….."/></Topic></RDF>

ResourcesResources

2. Netscape Navigator 5

Uses RDF to describe data used in browser (mailbox contents, directory contents)

As a way of adding dynamic data access

<rdf:RDF xmlns:rdf="http://www.w3.org/TR/WD-rdf-syntax#" xmlns:sm="http://www.mozilla.org/smart-mail/schema#"> <rdf:Description about="http://www.mozilla.org/smart-mail/….”> <sm:message id="4025293"> <sm:recipient>wat@netscape.com</sm:recipient> <sm:sender>helga@netcenter.net</sm:sender> <sm:received-by>wing.mcom.com</sm:received-by> <sm:subject>Recipe for Yam Soup!</sm:subject> <sm:body> http://www.mozilla.org/smart-mail/get-body.cgi?... </sm:body> </sm:message> <sm:message id="4025294"> <sm:recipient> wat@netscape.com </sm:recipient> <sm:sender>w2@pbox.ohio-state.edu</sm:sender> <sm:received-by>x-wing.mcom.com</sm:received-by> <sm:subject>We won our ultimate game</sm:subject> <sm:body> http://www.mozilla.org/smart-mail/get-body.cgi?... </sm:body> </sm:message> </rdf:Description></rdf:RDF>

Mailbox Mailbox EntriesEntries

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

An Introduction to RDF

The Resource Description Framework

Ian GRAHAMCentre for Academic TechnologyTel: 978-4548Email: <ian.graham@utoronto.ca>Talk: http://www.utoronto.ca/ian/talks/