rdfs:class versus owl:class in SOSA-Core

Hi,

Sorry for being so picky about this during our meeting but I do not want us
to take decisions that have consequences that we can not yet foresee.

To the best of my knowledge (and please correct me if I am wrong):

Under the semantics of OWL1, rdfs:class and owl:class are only equivalent
for OWL-Full. For OWL-DL (and OWL-Lite) owl:class is a subclass of
rdfs:class.

This means that every valid document in OWL will be a valid document in
RDFS, however *not* every rdfs:class is an owl:class. I do not want us to
end up in OWL-Full because of this.

For OWL2, I found this: 'owl:Class rdfs:subClassOf rdfs:Class . " (
https://www.w3.org/TR/owl2-rdf-based-semantics/). Things may be more
complicated here due to OWL2 punning and they may well turn out to be
equivalent, I will check this later.

If we decide to restrict ourself to only using RDFS for SOSA-core, and I am
not in favor of this, then we may have to go with rdfs:class. However, we
have not yet taken this decision and have also not discussed which axioms
and language to use for SSN. As Sosa-core and SSN will be aligned, this may
have more consequences that we should consider. It also seems like many of
us are in favor of using inverseOf, so we would be using OWL (and its
formal semantics) anyway. Note that this does not do any harm to an
RDFS-only tool/user as for those the inverseOf axiom will simply have no
formal semantics. Still all other triples that use both relations will
still be just fine.

Given the subclasssing, I do not see any problems using owl:class, but we
may accidentally end up in OWL-full or with being incompatible to the
standards if we opt for rdfs:class. Again, I am happy to be corrected. At
least, I do not see harm in simply using owl:class.

Finally, and from very pragmatic point of view: ontologies that are under
very heavy use such as the DBpedia ontology simply use owl:class and I have
not yet seen any issues or complaints about that. See, for example,
http://dbpedia.org/ontology/City "dbo:City    rdf:type    owl:Class ." The
same is true for the goodrelations ontology and so forth (but I admit that
this is due to the more complex axiomatization they use).

I hope this will start a productive discussion.

Thanks for reading,
Krzysztof