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DDC, SKOS, and Linked Data on the Web

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OCLC/ISKO-NA
Preconference
5 August 2008
DDC, SKOS, and Linked
Data on the Web
Michael Panzer
Global Product Manager,
Taxonomy Services
OCLC
Overview
1. Why transform the DDC into a SKOS vocabulary?
2. Creating URIs
1. What is a concept?
2. What is an information resource?
3. Analyzing DDC for modeling in RDF/SKOS
1. Identifying concepts
2. Aligning DDC elements with SKOS classes and properties
3. Modeling sematic relationships
4. Integration into RESTful web services (if we have time)
Why transform the DDC into a SKOS
vocabulary?
- Participation in “data web” is crucial for knowledge discovery
tools
- SKOS as publication format
- Enabling data interoperability
- Extensible, but “dumbing down” possible
- Hospitability for terminologies; agile publication possible as soon as
recommendation status is reached
- Broadening the base of Dewey use cases and users
- Rethinking access to KOS in general
Caution: Most research problems of semantic integration or
vocabulary construction neither solved nor touched by SKOS!
[Checklist: Webification of KOS]
(Infra-)Structural choke points
1. Design of identifiers
2. Design of verbal designators (“verbal plane”)
3. Data representation
4. Vocabulary enhancement
5. User contribution
6. Versioning
7. Vocabulary registries
Cool URIs for the DDC (lightning overview)
- Approaches to URI design
- Encoding resource metadata into URIs?
- Axiom of URI opacity
- Genericity of resources
- Dimensions of variance: time, language, format
- Framing of concept instantiation
- Role of Dewey classes for URIs
- Classes as center of identification for DDC concepts
- Information resources vs. non-information resources in web
architecture
Example URIs
- Generic URI
- http://dewey.info/class/338.4
- Specific time
- http://dewey.info/class/338.4/2007/05/25
- http://dewey.info/class/338.4/e22
- Specific time & language
- http://dewey.info/class/338.4/2007/05/25/about.en
- Specific time, language & format
- http://dewey.info/class/338.4/2007/05/25/about.en.skos
Example URIs
- Concept vs. representation URIs
- http://dewey.info/class/338.4/
- http://dewey.info/class/338.4/about
- Caveat: template still might change syntactically, e.g.
- http://dewey.info/class,2007-05/338.4?$lang=en&$format=skos
- Is the identifier strategy sound?
- Application to SKOS
Analyzing DDC for modeling in RDF/SKOS
What to include? What makes sense as Linked Data?
- DDC is fairly complex:
- Manual, external and internal tables, schedules, Relative Index, …
- Regular, optional numbers; number spans, centered entries, …
- Elaborate note structure
- Singled out as skos:Concepts right now:
- Listed schedule numbers (including built numbers)
- Number spans
- Centered entries
- Relative Index terms (in different namespace)
Analyzing DDC for modeling in RDF/SKOS
370.11
Education for specific objectives
370.113
370.1130941
370.1130973
skos:relatedMatch
370.113085
Vocational education
skos:relatedMatch
Parents--vocational education
Vocational education--Great Britain
Vocational education--United States
Mapped LCSH
Relative Index
Career education
Career development
Career education--United States
Career education
Career education--United States--Curricula
Education of employees
Core competencies
Employee development
…
Human resource development …
Vocational education
Vocational training centers
Analyzing DDC for modeling in RDF/SKOS
skos:notation
skos:prefLabel
370.113
Vocational education
Class here career education,
occupational training, vocational
schools
Class on-the-job training, vocational
training provided by industry in
331.2592
skos:related
For vocational education at secondary
level, see 373.246; for adult
vocational education, see 374.013
See also 331.702 for choice of
vocation; also 371.425 for vocational
guidance in schools
RDF model: Class (1)
<class/370.113/2007/12> a skos:Concept ;
skos:inScheme <scheme/2007/12> ;
dct:created "1996-06-01T00:00:00.0-05:00"^^<http://purl.org/dc/terms/W3CDTF> ;
dct:updated "2003-03-26T00:00:00.0-05:00"^^<http://purl.org/dc/terms/W3CDTF> ;
skos:notation "370.113"^^<ddc:Notation> ;
skos:prefLabel "Vocational education"@en ;
skos:broader <class/370.11/2007/12> ;
skos:narrower <class/370.113085/2007/12> ,
<class/370.1130941/2007/12> ,
<class/370.1130973/2007/12> ;
skos:related <class/331.2592/2007/12> ,
<class/373.246/2007/12> ,
<class/374.013/2007/12> .
RDF model: Class (2)
<class/370.113/2007/12> skos:relatedMatch
<http://tspilot.oclc.org/lcsh/sh%2085020255%20> ,
<http://tspilot.oclc.org/lcsh/sh%2000002431%20> ,
<http://tspilot.oclc.org/lcsh/sh%2085144178%20> ,
<http://tspilot.oclc.org/lcsh/sh%2096002453%20> .
RDF model: Class (3)
<class/370.113/2007/12> ddc:hasIndexTerm <index/Career%20development> ,
<index/Career%20education> ,
<index/Education%20of%20employees> ,
<index/Employee%20development> ,
<index/Human%20resource%20development> ,
<index/Job%20training> ,
<index/Occupational%20training> ,
<index/Retraining%E2%80%94vocational%20education> ,
<index/Staff%20development> ,
<index/Training%E2%80%94employee%20education> ,
<index/Vocational%20education> ,
<index/Vocational%20schools> ,
<index/Vocational%20training> ,
<index/Work%20training> .
RDF model: Class (0)
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix skos: <http://www.w3.org/2008/05/skos#> .
@prefix ddc: <http://dewey.info/schema-terms/> .
@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix dct: <http://purl.org/dc/terms/> .
@base <http://dewey.info/> .
ddc:hasIndexTerm rdfs:subPropertyOf skos:relatedMatch .
ddc:isIndexTermOf rdfs:subPropertyOf skos:relatedMatch ;
owl:inverseOf ddc:hasIndexTerm .
Extending
SKOS
RDF model: Relative Index Terms
<Concept rdf:about="index/Job%20training">
<inScheme rdf:resource="index/2007/12"/>
<prefLabel xml:lang="en">Job training</prefLabel>
<ddc:isIndexTermOf rdf:resource="class/370.113/2007/12"/>
</Concept>
<Concept rdf:about="index/Job%20training">
<related rdf:resource="index/Vocational%20education"/>
</Concept>
RDF model: Gathering assertions about a
resource
Modeling concept history events
- Tracking and exposing change processes for discovery
- Two recent positions:
- Tennis: Augmenting SKOS with generic skos:ConceptInstance
to indicate version- and vocabulary-specific skos:Concepts
- Voss: Pragmatic approach focusing on retrieval; linking
versions with skos:mappingRelation
Modeling concept history events
- Some problems
- Change on concept level
• Labels, relations, etc.
• Change on scheme (inter-concept) level
• Exhaustive change of concepts
• Complex relocation/discontinuation, splitting of concept (1-to-many)
• Simple relocation/discontinuation (1-to-1)
• Partial change of concepts
• Melding of a concept (integrating new topics, many-to-1)
• Extensive revisions (many-to-many)
Simple relocation/discontinuation
<Concept rdf:about="class/370.19/2007/12">
<inScheme rdf:resource="scheme/2007/12"/>
<dct:created rdf:datatype="http://purl.org/dc/terms/W3CDTF">1996-06-01T00:00:00.0-05:00</dct:created>
<dct:updated rdf:datatype="http://purl.org/dc/terms/W3CDTF">2001-03-13T00:00:00.0-05:00</dct:updated>
<notation rdf:datatype="ddc:Notation">370[.19]</notation>
<prefLabel xml:lang="en">Psychological principles</prefLabel>
<broader rdf:resource="class/370.1/2007/12"/>
<historyNote rdf:parseType="Resource">
<dct:isReplacedBy rdf:resource="class/370.15/2007/12"/>
</historyNote>
<historyNote rdf:parseType="Resource">
<dct:isReplacedBy rdf:resource="class/306.43/1996"/>
</historyNote>
</Concept>
Simple relocation/discontinuation
- Two different representations of concept history modeled by
skos:historyNote
- Some problems: unclear semantics, unclear relationships of
replacing concepts (succession, coordination?)
<historyNote rdf:parseType="Resource">
<dct:isReplacedBy rdf:resource="class/370.15/2007/12"/>
</historyNote>
<historyNote rdf:parseType="Resource">
<dct:isReplacedBy rdf:resource="class/306.43/1996"/>
</historyNote>
DDC in SKOS: Further Issues
- Non-assignable concepts (“node labels”): skos:Collection
and skos:member not usable
- SKOS somewhat underspecified as RDF vocabulary; much
has to be done by following best practice recommendations
- SKOS tool stack still rather thin; could change after W3C
draft recommendation cools off
Integration into Web Services
- Expressing semantic relationships by
- Explicit resource description (source: assertion)
- Implicit resource description (source: inference)
- Application logic, SPARQL patterns
- Identified by URIs that are not present in the RDF store, e.g.,
/ancestors, /children
- http://dewey.info/class/338.4/ancestors/about.en.skos
- Web service responses
- HTTP status codes
Service Semantics: Generic Resources
http://dewey.info/class/338.4
Thing
303 See Other
http://dewey.info/class/338.4/about
[300 Multiple Choices]
application/rdf+xml wins
RDF
Content-Location:
http://dewey.info/class/338.4/about.de.skos
Generic
Document
content
negotiation
text/html wins
HTML
200 OK
http://dewey.info/class/338.4/about.de.html
Service Semantics: Blunt Instruments
Resource
Resource
describes
describes
describes
IR
specifies
specifies
?
IR1
isVariationOf
IR1
IR2
(Could be made explicit with RDF statements)
IR2
Thank you!
Michael Panzer <mailto:panzerm@oclc.org>
RDF model: Gathering assertions about
resources
- Not everything has to be kept in one “record” in RDF
- Reconstructing the whole concept graph for an RI term
with SPARQL:
DESCRIBE <http://dewey.info/index/Job%20training>
RDF model: Gathering assertions about a
resource
Resulting graph (in Turtle):
@prefix skos: <http://www.w3.org/2008/05/skos#> .
@prefix ddc: <http://dewey.info/schema-terms/> .
<http://dewey.info/index/Job%20training> a skos:Concept ;
skos:inScheme <http://dewey.info/index/2007/12> ;
skos:prefLabel "Job training"@en ;
ddc:isIndexTermOf <http://dewey.info/class/370.113/2007/12> ;
skos:related <http://dewey.info/index/Vocational%20education> .
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