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Concept Scheme Labelling Interactions

This page provides explanation, discussion and background material for the issue "ConceptSchemeLabellingInteractions".

Can two different concepts in the same concept scheme have any lexical labels in common?

I.e. can two different concepts in the same concept scheme both have the same preferred lexical label? Can two different concepts in the same concept scheme both have the same alternative lexical label? Can a lexical label be preferred for one concept and alternative for a different concept in the same concept scheme? Can a lexical label be hidden for one concept and either preferred or alternative for a different concept in the same concept scheme?

Imagine the SKOS vocabulary consists of only skos:prefLabel, skos:altLabel, skos:hiddenLabel, skos:Concept, skos:ConcepScheme and skos:inScheme.

Now consider the following graph:

@prefix ex: <http://www.example.com/examples#>.
@prefix skos: <http://www.w3.org/2004/02/skos/core#>.

ex:fooscheme rdf:type skos:ConceptScheme.

ex:A rdf:type skos:Concept.
ex:A skos:prefLabel "orange"@en.
ex:A skos:scopeNote "The colour orange."@en.
ex:A skos:inScheme ex:fooscheme.

ex:B rdf:type skos:Concept.
ex:B skos:prefLabel "orange"@en.
ex:B skos:scopeNote "The citrus fruit."@en.
ex:B skos:inScheme ex:fooscheme.

This graph is not inherently inconsistent.

However, if we were to assume that ex:fooscheme was a thesaurus, and attempt to generate a thesaurus from this graph, following the conventions and notation of ISO 2788 and BS 8723, we would have a problem. The problem is that two concepts in the ex:fooscheme concept scheme have the same preferred lexical label, and we can't tell from the graph whether these two concepts are supposed to be different or not.

If we assumed that ex:A and ex:B were different concepts, we could not generate a thesaurus, because it is an axiom of thesaurus construction that each preferred term in a thesaurus has one and only one meaning, i.e. there is a one-to-one correspondance between preferred terms and concepts.

If we assumed that ex:A and ex:B were the same concept, we would get the following thesaurus:

orange
  SN The colour orange.
  SN The citrus fruit.

... which obviously violates the original intention.

Consider a different example:

@prefix ex: <http://www.example.com/examples#>.
@prefix skos: <http://www.w3.org/2004/02/skos/core#>.

ex:fooscheme rdf:type skos:ConceptScheme.

ex:A rdf:type skos:Concept.
ex:A skos:prefLabel "orange (colour)"@en.
ex:A skos:altLabel "orange"@en.
ex:A skos:scopeNote "The colour orange."@en.
ex:A skos:inScheme ex:fooscheme.

ex:B rdf:type skos:Concept.
ex:B skos:prefLabel "orange"@en.
ex:B skos:scopeNote "The citrus fruit."@en.
ex:B skos:inScheme ex:fooscheme.

Again, this graph is not inherently inconsistent.

However, problems arise when trying to generate a thesaurus from this graph. In this case it is simply not possible to generate the thesaurus under any assumption, because the lexical label "orange"@en would be mapped to both a preferred term and a non-preferred term. It is an axiom of thesaurus construction that a term must be either preferred or non-preferred.

Consider a third example:

@prefix ex: <http://www.example.com/examples#>.
@prefix skos: <http://www.w3.org/2004/02/skos/core#>.

ex:fooscheme rdf:type skos:ConceptScheme.

ex:A rdf:type skos:Concept.
ex:A skos:prefLabel "orange (colour)"@en.
ex:A skos:altLabel "orange"@en.
ex:A skos:scopeNote "The colour orange."@en.
ex:A skos:inScheme ex:fooscheme.

ex:B rdf:type skos:Concept.
ex:B skos:prefLabel "orange (fruit)"@en.
ex:B skos:altLabel "orange"@en.
ex:B skos:scopeNote "The citrus fruit."@en.
ex:B skos:inScheme ex:fooscheme.

Again, this graph is not inherently inconsistent.

Again, however, problems arise when trying to generate a thesaurus from this graph, which are summed up in SkosDesign/ThesaurusPatterns.


Summary

Thesauri are a major application of the SKOS vocabulary. However, to be usable as a thesaurus, an RDF representation has to observe some syntactic constraints on the usage of the SKOS vocabulary. These syntactic constraints should probably be optional, because other types of vocabulary may not need them, but we still have to say what they are.