SKOSCOMP34512

Sebastian Brandt (Slides by from Sean Bechhofer)

brandt@cs.manchester.ac.uksean.bechhofer@manchester.ac.uk

Friday, 2 May 2014

Terminology Management• Consider our original use case

– Building an index for a children’s book on animals– Target: Hierarchical controlled vocabulary

• I.e., a taxonomy• We used an ontology as the development KR

– Terms mapped to classes– The hierarchical relations were mapped to

subsumption– The fully classified class graph == the taxonomy

• Is this representationally adequate– For all controlled vocabularies?– For our index?

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A typical index

3http://www.anindexer.com/samples/captive/captive1.html

There is hierarchy

Are these subsumptions?

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Non-hierarchal relations!

4http://www.anindexer.com/samples/captive/captive1.html

“Related” terms.

Redirect

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Redirect?

5http://www.anindexer.com/samples/captive/captive1.html

Note that this relation is hierarchal!

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Terminology Management• Not all terminologies are the same!

– Data oriented• Intended to feed into databases• Intended to support statistical analysis• Logic seems to do rather well there

– Linguistically oriented• Mapping linguistic relations (WordNet)• Not very logical!

– E.g., terms have multiple senses– Navigationally oriented

• E.g., the Dewey decimal system• Cognitively salient relations

• Many terminologies serve multiple purposes6

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Navigation vs. Subsumption• Subsumption

– Based on the way the world is/model theoretic– Strict inclusion– Amenable to a logical treatment

• In particular, derivable from features of relational structures

• Navigation– Based on “how we think”– Associative

• Associations may be “hierarchal” (in some sense) or not– Generally “brute,” vague, & informal

• Derivable from patterns of behavior (sometimes)• Cognitive cow paths 7

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Desire Paths

8http://www.flickr.com/photos/bdunnette/6432035825/

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Catalogue

Terms/glossary

Thesauri

Informal is-a

Formal is-a

Frames

ValueRestrictions

ExpressiveLogics

A Spectrum of Representation

• Formal representations are not always the most appropriate for applications

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SKOS• SKOS: Simple Knowledge Organisation Scheme• Used to represent term lists, controlled vocabularies

and thesauri• Lexical labelling• Simple broader/narrower hierarchies,

no formal semantics• W3C Recommendation

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Primary Use Cases/ScenariosA. Single controlled vocabulary used to index and

then retrieve objects• Query/retrieval may make use of some structure

in the vocabulary

B. Different controlled vocabularies used to index and retrieve objects• Mappings required between the vocabularies

• Also other possible uses (e.g. navigation)

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SKOS Goals• to provide a simple, machine-understandable,

representation framework for Knowledge Organisation Systems (KOS)…

• that has the flexibility and extensibility to cope with the variation found in KOS idioms…

• that is fully capable of supporting the publication and use of KOS within a decentralised, distributed, information environment such as the world wide (semantic) web.

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Concept Schemes• A concept scheme is a set of concepts, potentially

including statements about relationships between those concepts– Semantic Relationships

• Broader/Narrower Terms• Related Terms

– Lexical Labels• Preferred, alternative and hidden labels

– Additional documentation• Notes, comments, descriptions

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SKOS Model

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Labelling• Lexical Labels associated with

Concepts – Preferred: one per language– Alternate: variants, – Hidden: mis-spellings

• Labels pairwise disjoint.

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Semantic Relations• Hierarchical and Associative• Broader/Narrower• Loose (i.e. no) semantics

– A publishing vehicle, not a set ofthesaurus construction guidelines

• broader/narrower not (inherently) transitive in SKOS

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Not (necessarily?!) transitive?• But, surely

– if A is broader than B– and B is broader than C– that A is broader than C!– i.e., TRANSITIVE!?

• Consider the Library of Congress Subject Organization– Vehicles broader than

• Cars broader than– Wheels

– Is “Vehicles” necessarily broader than “Wheels”?• (Not all wheels are vehicular...spinning wheels, potter’s wheels)• We might “fix” this by implicitly making the Wheels, “car wheels”

• Definitely not subsumptions all the way!– Vehicle to Cars, yes– Cars to Wheels is partonomic 17

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Mapping Relations• Subproperties of Semantic Relations• Intended for cross-scheme usage

• Although no formal enforcement• Usually there’s bespoke management code

• Or things are passed to the user

• exactMatch similar to EquivalentClasses• But again! Transitivity fail

• or transitivity “caution”

• broad- and narrowMatch• “like” subsumption

• Much more similar to “see”– or “see also”– The relationship isn’t reliable

• In the sense of having a semanticsFriday, 2 May 2014

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SKOS and OWL• SKOS and OWL are intended for different (but

related) purposes• SKOS Concept schemes are not formal ontologies in

the way that, e.g. OWL ontologies are formal ontologies.

• There is no formal semantics given for the conceptual hierarchies (broader/narrower)represented in SKOS.

• Contrast with OWL subclass hierarchies which have a formal interpretation (in terms of sets of instances).

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SKOS and OWL• SKOS Concepts not intended for instantiation in the same way

that OWL Classes are instantiated– Leo is an instance of Lion– Born Free is a book about Lions

• Concept Schemes allow us to capture general statements about things that aren’t necessarily strictly true of everything– It’s useful to be able to navigate from Cell to Nucleus, even

though it’s not the case that all Cells have a Nucleus– Relationships between Polio and Polio virus, Polio vaccine,

Polio disease…– Relationships between Accident and Accident Prevention,

Accidents in the Home, Radiation Accidents…• But we can’t necessarily draw the same kinds of inferences

about SKOS hierarchies. – Broader hierarchy is not transitive.

• Although mechanisms are available which allow us to query the transitive closure of the hierarchy.

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AnnotationGeneral

• Labels– Human readable

• Textual Definitions– Scope notes

• DC style metadata– authorship

• Change History• Provenance information

Application Specific

• Entry points for forms• Driving User interaction• Hiding engineering

aspects of the model• Methodological support

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SKOS as Annotation• SKOS labelling and documentation properties are

defined as OWL Annotation Properties– Preferred/Alternate/Hidden Labels– Documentation/Notes

• SKOS then provides a standardised vocabulary for annotating OWL ontologies

• Leverage existing tooling.– OWL API– Protégé

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SKOS and OWL• SKOS and OWL are intended for different purposes.• OWL allows the explicit modelling/description of a

domain• SKOS provides vocabulary and navigational structure• Annotation mechanisms allow them to coexist

– And even interact– A key modelling technique is exploiting OWL

knowledge to support SKOS relations

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Resources• SKOS:

– http://www.w3.org/TR/skos-reference/– http://www.w3.org/TR/skos-ucr/– http://www.w3.org/TR/2009/NOTE-skos-

primer-20090818/

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