Update on SKOS and Use Cases
Ecoterm, 5 October 2009
Antoine Isaac
Vrije Universiteit AmsterdamW3C Semantic Web Deployment working group
http://www.few.vu.nl/~aisaac
Preamble: acknowledgements
Participants of the W3C Semantic Web Deployment Working Group
Tom Baker, Guus Schreiber, Alistair Miles, Sean Bechhofer, Ralph Swick, Ed Summers, Jon Phipps, Margherita Sini, Diego Berrueta, Clay Redding, and many others…
http://www.w3.org/2006/07/SWD/
SWD working group goals
Various aspects of deploying Semantic Web technology:
• Publication guidelines– URI management
• Embedding RDF in (X)HTML pages– RDFa
• RDF representation of existing vocabularies – SKOS
SKOS
• Simple Knowledge Organization System
• SKOS is a model to represent KOSs on in RDF in a simple way– Not directly addressing complex terminological issues
SKOS is now an official W3C recommendation!
W3C standardization process
• Input: draft specification (SKOS 2005)• Collect use cases & derive requirements• Create issues list: requirements that cannot be handled
by the draft spec• Propose resolutions for issues• Get consensus on new spec• Find two independent implementations for each feature
in the spec• Continuously: asked for public feedback/comments
– Lot of feedback coming from [email protected]
Guus Schreiber
What then?
• Update on SKOS
Basic SKOS
• Concepts• Lexical properties • Semantic relations • Notes
Things that have remained quite stable since SKOS 2005
Example: SKOS graphanimals
NT catscats
UF domestic catsRT wildcatsBT animalsSN used only for domestic cats
domestic catsUSE cats
wildcats
skos:related
skos:broader
skos:scopeNote
"animals"@en
skos:prefLabel
ex:animals
"domestic cats"@en
skos:altLabel"cats"@en
skos:prefLabel
ex:cats
"used only fordomestic cats" "wildcats"@en
skos:prefLabel
ex:wildcats
Some other stable features
• Collections of concepts– skos:Collection, skos:OrderedCollection, skos:member
• Explicit representation of Concept Schemes– skos:ConceptScheme, skos:inScheme, skos:hasTopConcept
skos:hasTopConcept
skos:inScheme
skos:broader
skos:inScheme
ex:animals
ex:cats ex:animalVocabulary
New stuff
• Mapping relations
• SKOS-XL extension
• Discussion on semantics
• (Notations)
Mapping
• A crucial set of use cases, where semantic links across KOSs have to be exploited– Integrated navigation and search – Real-world cases:
Johan Stapel, Nat. Library of the Netherlands
Networking controlled vocabularies in SKOS
skos:exactMatch
skos:broadMatch
ex1:cats
ex1:animals ex2:animal
• closeMatch and exactMatch for equivalence– exactMatch is stronger and context-independent (transitive)
• broadMatch and narrowMatch for hierarchical links• relatedMatch for other cases of interest
Some were here in 2005, but as a non-stable extension
KOS 1:animalscatswildcats
KOS 2:animalhumanobject
From SKOS Use Cases:• Use Case #3 — Semantic search service across
mapped multilingual thesauri in the agriculture domain
“The AIMS project includes String-to-String relationships”
“Requires: R-RelationshipsBetweenLabels”
• In basic SKOS, labels are RDF literals and cannot be subjects of RDF statements
Relationships between lexical labels
Relationships between lexical labels
• Done as an extension: SKOS-XL– skos-xl:Label– skos-xl:labelRelation
skos-xl:labelRelationex:translation
Semantics for SKOS?
• The SKOS model gives formal constraints on SKOS data
• But SKOS must cope with existing information, and not infer new knowledge, beyond what KOS designers intend
• Minimal semantic commitment– Over-commitment harms interoperability
Example: semantics of labels
• SKOS assumes some characteristics for the different kinds of labels– A concept has only one prefLabel per language
"bêtes"@frskos:prefLabel
"animaux"@frskos:prefLabel
ex:animals
Example: semantics of broader• Is skos:broader "transitive"?
• It can be wrong, sometimes!– Some KOSs are not always hierarchically clean
• skos:broader is not transitive in general
ex:cats
ex:mammalsskos:broader
ex:animalsskos:broader
skos:broader
ex:cats
ex:mammalsskos:broader
ex:animalsskos:broader
skos:broader has a super-property skos:broaderTransitive with semantics of “has ancestors”– 1: every broader implies a broaderTransitive
– 2: broaderTransitive is transitive!
skos:broaderTransitive
skos:broaderTransitive
skos:broaderTransitive
Semantics of broader
What are the benefits?
• Semantic Web features applied to KOSs:– Web-oriented modeling– Re-use & sharing of resources (concepts!) and
descriptions of resources– Linking between resources from different contexts– Extensibility
What then?
• SKOS implementations
Current SKOS Implementations
• Report by SWD group– Implementations: tools to exploit or create SKOS data– Vocabularies: KOSs converted to SKOS
• 27 contributions– Give an idea on (early) usage of SKOS constructs– and on applications: mostly vocabulary services
SKOS Implementation Report
A blossoming field
The report is a partial snapshot, it misses a lot:• KOSs:
– NASA vocabularies– GEMET?– Agrovoc?
• Search applications: – Libris: http://libris.kb.se/– Europeana Thought Lab:
http://www.europeana.eu/portal/thought-lab.html
• Annotation tools
Next steps?
• By the community, for the community– Gathering exemplar conversions and publications– Extensions or good practices to deal with more specific
problems, like coordination• SKOS application profiles?
• Take-home message:
get (or remain) involved!
Thanks!
• Some links– SKOS homepage: www.w3.org/2004/02/skos/
Soon equipped with a community-oriented wiki!– SKOS Reference: www.w3.org/TR/skos-reference/ – SKOS Primer: www.w3.org/TR/skos-primer/
• A demo I could make:– LCSH as SKOS linked data : http://id.loc.gov– mapped to French RAMEAU: http://stitch.cs.vu.nl/rameau
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