1. SKOS and Linked Data
Antoine Isaac
ISKO, London, Sept. 14th 2010

2. Personal background Europeana
Web & Media Lab, Vrije Universiteit Amsterdam
W3C Library Linked Data group
( ) W3C Semantic Web Deployment group
SKOS

3. Towards a web of culture data

4. Government data again? http://standards.esd.org.uk/
electronic service delivery

5. Government data again?

6. SKOS Simple Knowledge Organization System
Scope: knowledge organization systems (KOS) such as thesauri, classification systems, subject heading lists…
SKOS is for representings KOSs in RDF in a simple way

7. Representing semantics
The formal way: OWL Semantic Web ontology language
Used for ontologies that enable machine reasoning
Mother is a class
It is the intersection of the classes Woman and Parent
Parent is the class of entities of type Person that are related to at least one other resource of type Person using the child property …

8. SKOS is not for formal ontologies
Turning KOSs into ontologies is possible, but KOSs
are large
have softer “semantics”
Parent RelatedTerm Child
have often a focus on terminological information
Child UsedFor Offspring
Softer semantics can be useful as such for many applications!
Semantic search, annotation…

9. Basic SKOS
A set of features common to various KOS types and useful for many applications
Concepts
Lexical properties
Semantic relations
Notes

10. Thesaurus example Animals cats UF (used for) domestic cats
RT (related term) wildcats
BT (broader term) animals
SN (scope note) used only for domestic cats
domestic cats
USE cats
wildcats

11. Concepts and labels cats UF (used for) domestic cats
skos: =
rdf: =
ex: =

12. Note: multilingual labels

13. Semantic relations cats RT (related term) wildcats
BT (broader term) animals

14. A SKOS graph animals cats UF domestic cats RT wildcats BT animals
SN used only for domestic cats
domestic cats
USE cats
wildcats

15. SKOS mappings SKOS allows bridging across KOSs from different contexts
animal
human
object
KOS 1:
animals
cats
wildcats

16. Other features Concept grouping Concept documentation
skos:Collection, skos:member…
Concept documentation
skos:example…
SKOS-XL: extension for more complex representation of labels
Note: SKOS can be extended as any other RDF vocabulary
32 constructs in total

17. Semantics for SKOS There are some basic constraints on SKOS data
E.g., a concept has only one prefLabel per language

18. Semantics for SKOS There are rules to infer new facts
E.g., broader and narrower are inverse of each other

19. Semantics for SKOS Minimal semantic commitment:
SKOS must cope with existing information and not infer new data beyond what KOS publishers intend

20. References SKOS Reference http://www.w3.org/TR/skos-reference
SKOS Primer
SKOS homepage
SKOS wiki
SKOS mailing list

21. Benefits of SKOS?
Easily fitting KOSs into the Semantic Web & Linked Data vision
Web-oriented representation
Re-use & sharing of concepts and their descriptions
Linking between concepts from different contexts

22. Demo Subject heading lists as SKOS linked data
American LCSH
French RAMEAU:
German SWD:
mapped using manual links from the MACS project
Starting from

28. Linked Data?
1. Use URIs as names for things 2. Use HTTP URIs so that people can look up those names 3. When someone looks up a URI, provide useful information using standards (RDF, SPARQL) 4. Include links to other URIs, so that they can discover more things Tim Berners-Lee,

31. SKOS Implementations
Miles, Bechhofer, SKOS Implementation Report, May 19th 2009

32. Some landmark SKOS implementations
Swedish National Library’s Libris catalogue and thesaurus
Library of Congress’ vocabularies, including LCSH
DNB’s Gemeinsame Normdatei (incl. SWD subject headings)
BnF’s RAMEAU subject headings
OCLC’s DDC classification and VIAF
STW economy thesaurus
National Library of Hungary’s catalogue and thesauri (example)
Wikipedia categories through Dbpedia
New York Times subject headings
IVOA astronomy vocabularies
GEMET environmental thesaurus
Agrovoc
Linked Life Data
Taxonconcept
UK Public sector vocabularies (e.g., )

33. KOS Alignments? Quite many of them are linked to some other resource
LCSH, SWD and RAMEAU interlinked through MACS mappings
GND -> DBpedia, VIAF
Libris -> LCSH
Agrovoc -> CAT, NAL, SWD, GEMET
NYT -> freebase, DBpedia, Geonames
dbPedia links are overwhelming
Hungary, STW, TaxonConcept, GND…

34. Issues: semantic alignment of SKOS data
In a linked data environment, the most interesting applications are the ones that cross contexts
Mapping data between concept schemes is still scarce
More efforts are needed
Automatic or manual or a mixture of both

35. Issues: linking KOS data to other resources
KOSs become valuable when they bring a “semantic layer” over other resources
E.g. books and the topics they are about
Existing links are often only implicit in the data—using labels of concepts not their identifiers
Semantic annotation with KOS should be a main target
Cf. Drupal’s taxonomy plug-in

36. Conclusion
Publication and linking of linked KOS data is still work in progress, but
We are now in position of realizing the issues and working towards solving them
We can start building applications that make use of the wealth of data already available or yet to come
Many KO resources to re-use and link to

37. Thank you!

38. Acknowledgements
Participants of the Semantic Web Deployment working group
Alistair Miles, Sean Bechhofer, Ed Summers, Tom Baker, Guus Schreiber…
Library of Congress
French National Library
German National Library
MACS team (Swiss National Library)
EuropeanaConnect project