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Update on SKOS and Use Cases. Ecoterm, 5 October 2009 Antoine Isaac Vrije Universiteit Amsterdam W3C Semantic Web Deployment working group http://www.few.vu.nl/~aisaac. Preamble: acknowledgements. Participants of the W3C Semantic Web Deployment Working Group

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Update on SKOS and Use Cases

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Update on skos and use cases

Update on SKOS and Use Cases

Ecoterm, 5 October 2009

Antoine Isaac

Vrije Universiteit Amsterdam

W3C Semantic Web Deployment working group


Preamble acknowledgements

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…


Swd working group goals

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

Update on skos and use cases


  • 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

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

What then?

  • Update on SKOS

Basic skos

Basic SKOS

  • Concepts

  • Lexical properties

  • Semantic relations

  • Notes

    Things that have remained quite stable since SKOS 2005

Example skos graph

Example: SKOS graph


NT cats


UF domestic cats

RT wildcats

BT animals

SN used only for domestic cats

domestic cats

USE cats


Some other stable features

Some other stable features

  • Collections of concepts

    • skos:Collection, skos:OrderedCollection, skos:member

  • Explicit representation of Concept Schemes

    • skos:ConceptScheme, skos:inScheme, skos:hasTopConcept

New stuff

New stuff

  • Mapping relations

  • SKOS-XL extension

  • Discussion on semantics

  • (Notations)



  • 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

Networking controlled vocabularies in SKOS

KOS 1:




KOS 2:




  • 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

Relationships between lexical labels

Relationships between lexical labels

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 labels1

Relationships between lexical labels



  • Done as an extension: SKOS-XL

    • skos-xl:Label

    • skos-xl:labelRelation

Semantics for skos

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

Example: semantics of labels

  • SKOS assumes some characteristics for the different kinds of labels

    • A concept has only one prefLabel per language

Example semantics of broader

Example: semantics of broader

  • Is skos:broader "transitive"?

  • It can be wrong, sometimes!

    • Some KOSs are not always hierarchically clean

  • skos:broaderis not transitive in general

Semantics of broader

Semantics of broader

skos:broaderhas a super-property skos:broaderTransitive with semantics of “has ancestors”

  • 1: every broader implies a broaderTransitive

  • 2: broaderTransitive is transitive!

What are the benefits

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 then1

What then?

  • SKOS implementations

Current 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

SKOS Implementation Report

A blossoming field

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

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!



  • 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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