DDC, SKOS, and Linked Data on the Web
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Transcript of DDC, SKOS, and Linked Data on the Web
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OCLC/ISKO-NA Preconference
5 August 2008
Michael PanzerGlobal Product Manager, Taxonomy ServicesOCLC
DDC, SKOS, and Linked Data on the Web
DDC, SKOS, and Linked Data on the Web
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OverviewOverview
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)
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Why transform the DDC into a SKOS vocabulary?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!
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[Checklist: Webification of KOS][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
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Cool URIs for the DDC (lightning overview)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
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Example URIsExample 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
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Example URIsExample 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
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Analyzing DDC for modeling in RDF/SKOSAnalyzing 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)
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Analyzing DDC for modeling in RDF/SKOSAnalyzing DDC for modeling in RDF/SKOS
370.11 Education for specific objectives
370.113 Vocational education
370.113085 Parents--vocational education
370.1130941 Vocational education--Great Britain
370.1130973 Vocational education--United States
Career development
Career education
Education of employees
Employee development
Human resource development …
Career education
Career education--United States
Career education--United States--Curricula
Core competencies
…
Vocational education
Vocational training centers
Relative Index
Mapped LCSH
skos:relatedMatch
skos:relatedMatch
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Analyzing DDC for modeling in RDF/SKOSAnalyzing DDC for modeling in RDF/SKOS
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
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
skos:notation
skos:prefLabel
skos:related
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RDF model: Class (1)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> .
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RDF model: Class (2)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> .
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RDF model: Class (3)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> .
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RDF model: Class (0)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
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RDF model: Relative Index TermsRDF 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>
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RDF model: Gathering assertions about a resourceRDF model: Gathering assertions about a resource
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Modeling concept history events 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
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Modeling concept history eventsModeling 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)
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Simple relocation/discontinuation 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>
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Simple relocation/discontinuationSimple 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>
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DDC in SKOS: Further IssuesDDC 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
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Integration into Web ServicesIntegration 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
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Service Semantics: Generic ResourcesService Semantics: Generic Resources
http://dewey.info/class/338.4
http://dewey.info/class/338.4/about
Thing
Generic Document
303 See Other
RDF HTML
Content-Location:
http://dewey.info/class/338.4/about.de.skoshttp://dewey.info/class/338.4/about.de.html
content negotiation
application/rdf+xml wins text/html wins
200 OK
[300 Multiple Choices]
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Service Semantics: Blunt InstrumentsService Semantics: Blunt Instruments
IR1 IR2
Resource
describes
IR
specifies
isVariationOf
specifiesIR1 IR2
Resource
describes
?
describes
(Could be made explicit with RDF statements)
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RDF model: Gathering assertions about resourcesRDF 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>
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RDF model: Gathering assertions about a resourceRDF 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> .