Imports in SKOS
This page is about ISSUE-119 SkosImports
Current situation
The SKOS WD [1] includes discussion about the use of owl:imports (in particular the fact that importing a skos:ConceptScheme does not necessarily import skos:inScheme links). The SKOS Primer [2] suggests the use of owl:imports for extending/re-using a concept scheme.
Discussion
skos:ConceptScheme is defined as an owl:Class. The domain and range of owl:imports is owl:Ontology. Thus asserting that a concept scheme imports another via owl:imports leads to the consequence that the instances of skos:conceptScheme involved in the import are also instances of owl:Ontology. This in turn results in an OWL Full ontology (due to the dual use of a URI as a class and ontology).
As discussed in [3], under the OWL Full semantics, the intended interpretation of owl:imports is that the rdf graph retrieved from the imported URI is added to importing graph. Users should be aware of this and any alternative interpretations should be avoided.
A skos:ConceptScheme is an aggregation of one or more conceptual resources, while an owl:Ontology is a collection of axioms describing a set of models. Is it desirable to consider something as both a skos:ConceptScheme and owl:Ontology? See also SkosDesign/ConceptSchemes.
There is some relationship here with ISSUE 80 SKOS-OWL Patterns
Other approaches
ISSUE-119 raises the possibility of "rolling our own" skos:imports. I would hesitate to do so. This introduces additional vocabulary that may introduce confusion and would need a clear rationale that distinguishes it from owl:imports.
Alternatively, if the intention is to direct the user/application to a resource that provides additional useful information (although not necessarily definitional), rdf:seeAlso could be used. This would then leave the decision as to exactly what to do with the referenced scheme in the hands of the application.
Resolution
The situation was resolved during the Washington F2F [4]. Reference to owl:imports will be removed from Reference, and additional text explaining the situation will be added to the primer.
Proposed text can be found in imports20080515.html. This should replace the last two paragraphs of Section 3.1 in the current Primer [5].
References
[1] http://www.w3.org/TR/2008/WD-skos-reference-20080125/#L1170
[2] http://www.w3.org/TR/2008/WD-skos-primer-20080221/#secextension
[3] http://www.w3.org/2007/OWL/wiki/Imports#OWL_1.0