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 public-esw-thes@w3.org

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