In knowledge organization systems, sometimes concepts are merged (for
example, because the differences between concepts are not considered
significant any longer). Normally, a "weaker" concept, say A, is bound
to perish and gets some note attatched "Out of use, please use B".

How to put this on to the Linked Data Web?(*) Here our ideas:

<A> a skos:Concept ;
    rdfs:label "Real Estate Loan"@en ;
    owl:deprecated "true"^^xsd:boolean ;
    dcterms:isReplacedBy <B> ;
    skos:historyNote "deprecated in version 8.06"@en ;
    skos:inScheme <C> .

<B> a skos:Concept ;
    skos:prefLabel "Mortgage"@en ;
    skos:altLabel "Real Estate Loan"@en ;
    skos:inScheme <C> .
<C> a skos:ConceptScheme ;
    owl:versionInfo "8.06" .

The main goal was that people/applications who use the concepts of a KOS
(e.g. with dcterms:subject) should be able to automatically discover
deprecated concepts and to replace them by currently valid ones. The
approach does not aim at an machine-readable record of historical states
and state transitions of the KOS and its concepts.

Some design decisions that could be questioned:

1) The former prefLabel of <A> has been moved to <B> as an altLabel. As
far as I can see, the spec doesn't prohibit using it also as a prefLabel
for <A>, but it feels more appropriate to avoid this by using a plain
rdfs:label. (As a nice side effect, concept <A> doesn't show up when the
KOS is queried for prefLabel/altLabel/hiddenLabel)

2) All skos:semanticRelations (broader, narrower, related etc.), and
also all skos:altLabel/hiddenLabels, were removed from the deprecated
concept A and, where appropriate, attached to concept B. 

3) A deprecated skos:Concept still is a skos:Concept (may be in use as
such; especially, may have still mappings from other vocabularies,
outside the scope of the actual KOS)

4) Versioning is done in a very informal way by attaching
owl:versionInfo to the skos:ConceptScheme. The skos:Concepts are
deliberately not versioned, because this would put a heavy burden on
their use. Also, the skos:ConceptScheme <C> currently does not have a
"versioned" URI (which could be done, but I'm not sure if it would be
worth the increased complexity). The history is only represented
informally in a skos:historyNote.

5) Prior versions of the skos:ConcpetScheme are on the web for
reference, however, the URIs for concepts and the scheme itself resolve
to the current version. (We will try to prohibit indexing of prior
versions by semantic search engines in order to avoid the aggregation of
not longer valid attributes and relations for a concept)

I wonder what you think about this approach.

Cheers, Joachim

* Some work to build on has been collected at

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