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Using SKOS in practice, with examples from the classification domain
Antoine Isaac
Aida Slavic
UDC Seminar 2009
SKOS
• Simple Knowledge Organization System
• SKOS is a model to represent KOSs on in RDF in a simple way– Not aimed at fitting everything!– Not aimed at replacing existing (non-web) formats!
• Now an official W3C recommendation
SKOS basis
SKOS offers a vocabulary for
• Concepts and concept schemes
• Labels
• Semantic relations
• Notes
Networking controlled vocabularies in SKOS
Matching properties as conceptual relations
skos:exactMatch
skos:broadMatch
ex1:cats
ex1:animals ex2:animal
KOS1animalscatswildcats
KOS2animalhumanobject
The relevance of networked KOSs
Johan Stapel, Koninklijke Bibliotheek, Den Haag
Pointers to SKOS deployments
• SKOS implementation reportwww.w3.org/2006/07/SWD/SKOS/reference/20090315/implementation.html
• Library of Congress Subject Headingslcsh.info
• RAMEAU subject headingsstitch.cs.vu.nl/rameau
• DDCdewey.info
SKOS conversion example: NBC
Dutch Basic Classification
21.50 Sculpture: general21.51 Techniques and materials
Representing classes as concepts
rdf:type
nbc:21.51
skos:Concept
21.51 Techniques and materials
Relationships between classes
21.50 Sculpture: general21.51 Techniques and materials
skos:broader
rdf:type
nbc:21.50
skos:Concept
rdf:type
nbc:21.51
skos:Concept
Issues with SKOS representation of classifications
• Captions and labels• Languages• Time versions of classes• Coordination of classes• Auxiliary elements• …
Issue 1: notations, captions and labels
• SKOS enables representing notations• And human-readable preferred (or alternative)
labels, suited for captions
21.51 Techniques and materials
"21.51"^^nbc:notationskos:notation
nbc:21.51
skos:prefLabel"techniques andmaterials"@en
Different choices for notations?
• Can notations be SKOS preferred labels?– They make sense for users & can be displayed
• We can represent them as language-neutral labels
skos:prefLabel "21.51"
"21.51"^^nbc:notationskos:notation
nbc:21.51
skos:prefLabel"techniques andmaterials"@en
Several choices!
Issue 2: Multiple languages
SKOS concepts can have labels in various languages
"21.51"^^nbc:notationskos:notation
nbc:21.51
skos:prefLabel"techniques andmaterials"@enskos:prefLabel
"technieken enmaterialen"@nl
Issue 2: Multiple languages
On dewey.info: one concept per class & language
rdf:type
rdf:type
"641"^^ddc:notationskos:notation
ddc:641/2009/08/about.en
skos:prefLabel"Food & drink"@en
skos:Concept
"641"^^ddc:notationskos:notation
ddc:641/2009/08/about.fr
skos:prefLabel "Nourriture etboisson"@fr
skos:Concept
Several choices!
Issue 2: Multiple languages
Introducing an abstract entity that denotes the time/language-independent class
"641"^^ddc:notationskos:notation
ddc:641/2009/08/about.en
skos:prefLabel "Food & drink"@en
"641"^^ddc:notationskos:notation
ddc:641/2009/08/about.fr
skos:prefLabel "Nourriture etboisson"@fr
ddc:641/
dct:isVersionOf
dct:isVersionOf
Using Dublin Core's isVersionOf link
In RDF, it is possible to use other models in combination with SKOS…
Raising difficult issues: what is a "concept"?
• An artifact– used in descriptions, e.g., as subjects– used as a cluster for different labels with a similar
meaning – in semantic relationships with other concepts
• basis for Knowlegde Organization Systems
• What qualifies as a concept for DDC? For UDC?• Can different choices be done?
Issue 3: Tracking modifications2 RELIGION. FAITHS
21/28 CHRISTIANITY
21 Natural theology. Theodicy. De Deo 22 The Bible. Holy scripture 23 Dogmatic theology24 Practical theology 25 Pastoral theology 26 Christian church in general 27 General history of the Christian church
28 Christian churches, sects 29 NON CHRISTIAN RELIGIONS
NOW.....
2 RELIGION. FAITHS21 Prehistoric and primitive religions22 Religions of the Far East 23 Religions of the Indian subcontinent 24 Buddhism 25 Religions of antiquity 26 Judaism 27 Christianity 28 Islam 29 Modern spiritual movements
Creating representations of the versions
Each time-specific version should be a skos:Concept because:
• They are related to other (versions of) classes • Classification act refers to a time-specific version
A book on the Bible would be wrongly classified by "22" if "22" is the notation for "Far Eastern Religions"
"22"^^udc:notationskos:notation
udcmrf:22_17054
skos:prefLabel"Bible"@en
"22"^^udc:notationskos:notation
udcmrf:22_16544
skos:prefLabel"Far East
religions"@en
dct:isReplacedBy
IF WE FOCUS ON NOTATION... 22
Representing versions of classes
Using Dublin Core's isReplacedBy link
udcmrf:reference/22
"22"^^udc:notationskos:notation
udcmrf:22_17054
skos:prefLabel"Bible"@en
"22"^^udc:notationskos:notation
udcmrf:22_16544
skos:prefLabel "Far Eastreligions"@en
dct:isReplacedBy
dct:isVersionOf
dct:isVersionOf
Notations as a reference
Notations as aggregations
Notations can be seen as hubs for time-specific version of classes
udcmrf:reference/22
"22"^^udc:notationskos:notation
udcmrf:22_17054
skos:prefLabel"Bible"@en
"22"^^udc:notationskos:notation
udcmrf:22_16544
skos:prefLabel "Far Eastreligions"@en
dct:isReplacedBy
ore:aggregates
ore:aggregates
Using the aggregates link
from Object Reuse & Exchange (ORE) initiative
Tracking "Far East religions" in UDC database
CLASS ID: 16544
NOTATION: 22
DESCRIPTION:Religions originating in the Far East
*REPLACES: 299.5 DESCRIPTION: Religion of Oriental peoples ID: 15999
NOTATION HISTORY [22]: YES OLD DESCRIPTION: Bible
There is interesting history information (incl. IDs) in the vocabulary management system!
Concepts across notations
• "Far East religions" existed before: 299.5 • It does not belong to 22 alone
• There is a more abstract Far East Religion entity– its conceptual content may be updated while it keeps
its position in the hierarchy– it might be moved in the notation hierarchy and retain
its conceptual content
"22"^^udc:notation
skos:notation
udcmrf:22_16544
skos:prefLabel
"Far Eastreligions"@en
"299.1"^^udc:notation
skos:notation
udcmrf:299.1_15999
skos:prefLabel
"Religions ofOriental
Peoples"@en
dct:isReplacedBy
Representing concepts across notations
Towards stable abstract concepts?
"22"^^udc:notation
skos:notation
udcmrf:22_16544
skos:prefLabel
"Far Eastreligions"@en
"299.1"^^udc:notation
skos:notation
udcmrf:299.1_15999
skos:prefLabel
"Religions ofOriental
Peoples"@en
dct:isReplacedBy
udc:concept-FarEastReligion
dct:isVersionOf dct:isVersionOf
udcmrf:reference/22
"22"^^udc:notationskos:notation
udcmrf:22_17054
skos:prefLabel"Bible"@en
"22"^^udc:notation
skos:notation
udcmrf:22_16544
skos:prefLabel
"Far Eastreligions"@en
dct:isReplacedBy
ore:aggregates
ore:aggregates
"299.1"^^udc:notation
skos:notation
udcmrf:299.1_15999
skos:prefLabel
"Religions ofOriental
Peoples"@en
dct:isReplacedBy
udc:concept-FarEastReligion
dct:isVersionOf dct:isVersionOf
Two different versioning & aggregation mechanisms at work
Conclusion
• SKOS is an interoperability enabler• There are still issues
Different conversions reveal different choices
• But that's not a new problem, reallyStandardization often needs best practices & use cases
• Now, it is easier to publish and compare dataAs data is (will be) linked, it is even crucial to do it!
Interaction between information experts and techies is crucial
Thank you!
• Questions?
Drawing inspiration from• Joseph Tennis & Stuart Sutton• Michael Panzer• Jakob Voss