Download - An Introduction to RDF:
An Introduction to RDF:
The Resource Description Framework
Ian GRAHAMCentre for Academic TechnologyTel: 978-4548Email: <[email protected]>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
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” “[email protected]”
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:> [email protected] </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” “[email protected]”
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>[email protected]</sm:recipient> <sm:sender>[email protected]</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> [email protected] </sm:recipient> <sm:sender>[email protected]</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: <[email protected]>Talk: http://www.utoronto.ca/ian/talks/