An Introduction to RDF

1
Introduction to RDF
(Based closely upon an earlier presentation by
Eric Miller of OCLC)
Paul MillerUK Office for Library Information
Networkingp.miller_at_ukoln.ac.uk
Thomas HofmannAustralian Museums
On-Linethomash_at_amol.org.au
2
Metadata Definition

• Traditionally
• metadata has been understood as Data about Data
• Example(s)
• a library catalogue contains information
  (metadata) about publications (data)
• a file system maintains permissions (metadata)
  about files (data)

3
Metadata Definition (Cont.)

• Metadata describes other data
• One applications metadata is another
  applications data
• Metadata can itself be described by metadata (but
  that doesnt make it meta-metadata)
• Example
• Price lists (metadata) have expiration dates
  metadata about metadata. It is still just
  metadata.

4
Applications of Metadata

• Cataloguing (Item and Collections)
• Resource Discovery
• Electronic Commerce
• Intelligent Software Agents
• Digital Signatures
• Content Rating
• Intellectual Property Rights
• Privacy Preferences Policies

5
Application Item and Collection Cataloguing

• Describing individual resources
• documents, pages, images, audio files, etc.
• Describing the content of collections
• Web sites, databases, directories, etc.
• Relationships among Resources
• Tables of Content, chapters, images.
• Site Maps
• e.g. CIMI collection records

6
Application Resource Discovery

• Search engines can better understand the
  contents of a particular page
• More accurate searches
• Additional information aids precision
• Makes it possible to automate searches because
  less manual weeding is needed to process the
  search results

7
Application Electronic Commerce

• Metadata can be used to encode information needed
  in all stages of electronic commerce
• locating seller/buyer product
• searching yellow pages
• agreeing on terms of sale
• prices, terms of payment, contractual information
• transactions
• delivery mechanisms, dates, terms

8
Application Intelligent Agents

• representation and sharing of knowledge
• knowledge exchange
• modelling
• communication
• user-to-agent, agent-to-agent, agent-to-service
• resource discovery
• gives web-roaming agents the ability to
  understand their environment

9
Application Digital Signatures

• These are key to building the Web of Trust
• Required by
• agents
• electronic commerce
• collaboration
• RDF will become the preferred way to encode
  digital signatures on documents and on statements
  about documents

10
Application Content Rating

• Empowering users to select which kinds of web
  content they wish to see
• Child Protection
• W3C PICS (Platform for Internet Content
  Selection) working group
• US Communications Decency Act of 1996
• simple metadata architecture
• precursor to RDF

11
Other Applications

• Privacy Preferences and Policies
• describing a users willingness/reluctance to
  disclose information about himself/herself
• describing a site administrators desire to
  gather information about visiting users
• Intellectual Property Rights
• contractual terms related to usage and
  distribution rights to a document

12
Metadata Transmission
13
Metadata Assertions

• Metadata requirements will evolve
• The Web is machine-readable but not
  machine-understandable
• Metadata is useful
• e.g A lot could be gained from structured
  description of pages, servers, search services,
  and other resources
• See point 1

14
Introducing RDF

• Improve on PICS, HTML, and XML
• Machine understandable metadata
• Support structured values
• Support metadata bureaux
• Encourage authenticated metadata
• Base for a variety of descriptions
• cataloging, privacy, accessibility, IPR, ...

15
Data Integration

• Example
• The author of a document is Paul
• Paul is the author of a document
• A document is authored by Paul
• The author of a document is Paul
• Representation(s) in XML

ltdocument href http//doc_url author
Paul /gt
ltdocumentgt ltauthorgt ltnamegt Paul
lt/namegt lt/authorgt lturlgt http//doc_url
lt/urlgt lt/documentgt
ltauthorgt lturlgt http//doc_url lt/urlgt
ltnamegt Paul lt/namegt lt/authorgt
16
Data Integration (cont.)

• Complexity of querying XML documents
• N ways of mapping XML to logical structure
• Requires the normalization of all possible
  representations for effective query
• Mean the same thing to a person
• Mean very different things to a machine
• RDF much less flexible
• less flexible more interoperable!
• consistent way of representing statements

17
RDF Components

• Formal data model
• Syntax for interchange of data
• Schema Type system (schema model)
• Syntax for machine-understandable schemas
• Query and profile protocols

18
RDF Data Model

• Imposes structural constraints on the expression
  of application data models
• for consistent encoding, exchange and processing
  of metadata
• Enables resource description communities to
  define their own semantics
• Provides for structural interoperability

19
RDF Data Model

• Directed labelled graphs
• Model elements
• Resource
• Property
• Value
• Statement

20
RDF Model Primitives
Resource
Property
Value
21
Simple Example
Resource
Author
Paul
22
RDF Syntax

• RDF Model defines a formal relationships among
  resources, properties and values
• Syntax is required to...
• Store instances of the model into files
• Communicate files from one application to another
• W3C XML eXtensible Markup Language
• http//www.w3.org/XML

23
RDF Model Example 1
URIR
Title
RDF Presentation
Creator
Paul Miller
24
RDF Syntax Example
URIR
Title
RDF Presentation
Creator
Paul Miller
ltRDF xmlns http//www.w3.org/TR/WD-rdf-syntax
xmlnsdc http//purl.org/dc/element
s/1.0/gt ltDescription about URIRgt
ltdcTitlegt RDF Presentation lt/dcTitlegt
ltdcCreatorgt Paul Miller lt/dcCreatorgt
lt/Descriptiongt lt/RDFgt
25
RDF Model Example 2
URIR
Title
RDF Presentation
Creator
Paul Miller
26
RDF Syntax Example 2
ltRDF xmlns http//www.w3.org/TR/WD-rdf-syntax
xmlnsdc http//purl.org/dc/element
s/1.0/ xmlnsbib http//www.bib.org
/personsgt ltDescription about URIRgt
ltdcTitlegt RDF Presentation lt/dcTitlegt
ltdcCreatorgt ltDescriptiongt
ltbibNamegt Paul Miller lt/bibNamegt
ltbibEmailgt p.miller_at_ukoln.ac.uk lt/bibEmailgt
ltbibAff resource http//www.ukoln.ac.uk
/gt lt/Descriptiongt lt/dcCreatorgt
lt/Descriptiongt lt/RDFgt
27
RDF Model Example 3
URIR
Title
RDF Presentation
Creator
Eric Miller
28
Where do you stop?

• Model provides enabling technology
• Degree of metadata simplicity/complexity is a
  matter of
• Resource description communities needs,
  best-practice and experience
• Organization/Institutions Policy
• Economics
• Goals and requirements of implementation

29
RDF Schemas

• Declaration of vocabularies
• properties defined by a particular community
• characteristics of properties and/or constraints
  on corresponding values
• Schema Type System - Basic Types
• Property, Class, SubClassOf, Domain, Range
• Minimal (but extensible) at this time
• minimize significant clashes with typing system
  designed for XML NG DTDs (1999?)
• Expressible in the RDF model and syntax

30
Schema Vocabularies

• Enables communities to share machine readable
  tokens and locally define human readable labels.

dcCreator
31
Relationships among vocabularies
dcCreator
marc245
msKgrip
bibAuthor
32
Relationships among vocabulary elements
URIR
msKgrip
John Smith
33
Bringing it together

• RDF Metadata transmission
• Embedded (e.g. ltMETAgt), Transmitted with resource
  (HTTP), Trusted 3rd Party (HTTP GET)
• RDF Data Model
• Support consistent encoding, exchange and
  processing of metadata critical when aggregating
  data from multiple sources
• RDF Schema
• Declare, define, reuse vocabularies

34
RDF Summary

• RDF is a general-purpose framework
• RDF provides structured, machine-understandable
  metadata for the Web
• Metadata vocabularies can be developed without
  central coordination
• RDF Schemas describe the meaning of each property
  name
• Signed RDF is the basis for trust

35
RDF Information

• W3C RDF Model and Syntax Speciation
• Recommendation Status Feb 24, 1999
• W3C RDF Schema Specifications
• Proposed Recommendation Status Mar 4, 1999
• W3C RDF Home Page
• http//www.w3.org/RDF/

36
RDF and the Dublin Core

• RDF
• Dublin Core
• Overview
• Data Model
• Examples
• Qualification Mechanisms

37
Dublin Core Data Model

• Application of the RDF Data Model
• Sufficient richness in RDF to support Dublin Core
  modelling goals
• Defines implementation and extensibility
  framework for Dublin Core based applications
• CIMI is an example of these applications
• MICI could be an example of these applications

38
DC Data Model Qualifiers

• Element Qualifier (and Terms)
• Value Qualifier (and Terms)
• Value Types (and Terms)
• Value Components
• Language

39
The Dublin Core Data Model as RDF
40
An example for Date
41
An example for Relation
dcRelation
rdfValue
R
http//parent
dcqRelationType
IsPartOf
42
Element Qualifier (and Terms)

• Enabling mechanisms in the data model that
  support the qualification of the element relating
  the resource and the value
• e.g. The term Illustrator may be used to
  qualify the Creator element that relates some
  resource and some value
• Terms
• Resource identifying Illustrator

43
Value Qualifier (and Terms)

• Identifies the encoding, parsing and/or
  processing rules associated with a value
• LNF Lastname,spFirstname
• ISO8601 1998-10-01
• DDC 325.251
• AAT ionic column
• Terms
• Resources defining LNF, ISO8601, DDC, AAT, etc.

44
Language

• Defines the Language of the value
• langfr chat vs. langen chat
• XML provides a way of handling of language
  (xmllang)
• RDF adopts this, DC adopts this

45
What do you get for this?

• The separation of these constructs is important
  for extensibility by other resource description
  communities
• Dublin Core Metadata Initiative will not define
  an all inclusive set Terms
• It will define a canonical set and the enabling
  mechanisms for other communities to extend these

46
RDF Data Model

• Designed to impose structural constraint on
  syntax to support consistent encoding, exchange
  and processing of metadata
• Enables resource description communities to
  define their own semantics
• Provides for structural interoperability

Resource
Property
Value
47
Dublin Core Data Model
http//purl.org
dcCreator
Paul Miller
48
Dublin Core Data Model
http//purl.org
SN_001
dcCreator
rdfValue
Paul Miller
49
Dublin Core Data Model
http//purl.org
SN_001
dcCreator
rdfValue
Paul Miller
dcq CreatorType
dctIllustrator
50
Dublin Core Data Model
http//purl.org
SN_001
dcCreator
rdfValue
Miller, Paul
dcq AgentType
dcq AgentScheme
dctIllustrator
dctLNF
51
Dublin Core Data Model
http//purl.org
SN_001
dcCreator
rdfValue
Miller, Paul
rdfType
dcq AgentType
dcq AgentScheme
dctPerson
dctLNF
dctIllustrator
52
Dublin Core Data Model
http//look.org
SN_001
http// 411.org/ pmiller
dcCreator
rdfValue
dcqType
Author
53
Dublin Core Data Model
http//look.org
SN_001
http// 411.org/ pmiller
dcCreator
rdfValue
dcqType
Author
54
Dublin Core Data Model
http//look.org
http// rdf.411.org/ pmiller
dcCreator
dcqCreatorType
dctIllustrator
55
Dublin Core Data Model
A.
vcfn
http//look.org
dcCreator
http// rdf.411.org/ pmiller
vcmn
Paul
vcln
dcqCreatorType
Miller
dctIllustrator
56
Dublin Core Data Model
http//look.org
http// rdf.411.org/ pmiller
dcCreator
dcqCreatorType
57
Dublin Core Data Model
http//look.org
http// rdf.411.org/ pmiller
dcCreator
dcqCreatorType
dctAuthor
rdf_1
rdfType
Bag
rdf_2
cimisculptor
58
Key Data Model Decisions

• Application of RDF Data Model
• DC namespace defines the core elements
• http//purl.org/dc/elements/1.0/
• DCQ namespace defines the Dublin Core qualifier
  and extensibility mechanisms
• http//purl.org/dc/qualifiers/1.0/
• DCT namespace defines the Dublin Core terms and
  extensibility mechanisms
• http//purl.org/dc/terms/1.0/

59
Key Data Model Open Issues

• There still a few
• Dublin Core Data Model Working Draft
• out in April
• DC Proposed Recommendation shortly after
• Dublin Core Data Model Home Page
• http//purl.org/dc/groups/datamodel.htm

60
Additional Information

• RDF Home Page
• http//www.w3.org/RDF
• Dublin Core Metadata Initiative
• http//purl.org/dc/