SKOS concepts are likeky to somehow 'match' similar individuals in
other KOS, and singularly OWL ontologies. This question has already
been discussed with no clear answer on what should be a
sound/recommended/best practice. I'm currently working on a typical use
case which will maybe help to illustrate this difficult issue, namely
geographical-administrative entities. The project involves the French
National Institute for Statistics and Economic Studies (INSEE) ,
which is the official provider of facts and figures concerning the
country and its administrative subdivisions. The project aims to define
a RDF representation of the involved entities, unformally but precisely
defined by INSEE in its 'Code Officiel Géographique' .
Administrative structure of France being quite complex and
multi-hierarchical, capturing it in a KOS is quite a challenge, and
seems to need all the expressive power of OWL. The ontology of those
entities relies on a backbone of 'administrative subdivision'
relationships, and a bunch of constraints over those, such as : A
'department' subdivision is an instance of 'arrondissement', with a
'chef-lieu' (instance of 'city') which is either the unique department
'prefecture' or a 'sous-prefecture' etc ... The ontology has also to be
extensible to similar entities in other countries, supporting e.g. the
European nomenclature of NUTS .
Such constraints are useful to control ontology integrity, but many
'light-semantic' applications, such as search engines, will need
actually only a simplified view of this ontology, with thesaurus-like
relationships between entities, used for semantic expansion of search.
For such uses, a SKOS representation of geographical entities and their
hierarchy would be good enough, and such a representation could be
proposed as a 'simplified view' of the ontology.
So the question is : what should be the (recommended) practices to
provide such a simplification? Two main options :
Don't do that! different uses, different semantics, different
represenations. Entities in the SKOS representation should be defined
independently of the entities in the OWL ontology, with different URIs
supporting different semantics. A city is not a concept, having an
individual both of type skos:Concept and a:Geo-entity is not a good
Do it for semantic integration : same individual, one URI. The
OWL representation and the SKOS representation will not be used by the
same applications anyway, so there is no practical risk in having
individuals being declared of type skos:Concept in thesaurus-like
vocabularies (SKOS), and of type a:Geo-entity in ontology-like
vocabularies (OWL). Having a single URI would be useful in an
integrated environment using both indexing and search of documents
indexed on geo-entities, and semantic query and inference on these
Option 1 is safer, but raises the issue of semantic integration. How
will I assert that this SKOS concept and that OWL entity are somehow
representing the 'same' individual, and what is the meaning of this
'same-ness'? I won't push again 'hubjects' here, although I could ;-) . Option 2 is my
favorite those days, following the arguments pushed lately by Pat Hayes
. But what I wonder is to which extent the 'simple' SKOS classes and
properties should be tied to the 'complex' OWL classes and properties,
for instance should we
Declare a:Geo-entity as a subclass of skos:Concept ?
Declare a:subdivisionOf as a subproperty of skos:broader ?
Declare a:neighbor as a subproperty of skos:related ?
Such declarations could be useful for OWL-to-SKOS migration, but are
likely, if included in the OWL framework, to bring unsuspected and
weird entailments ...