Re: rdfs:class versus owl:class in SOSA-Core

Hi Krzysztof,

Thanks for your detailed explanations below!

Just to clarify, the intention in the meeting to go through a list of what constructs should be in SOSA (as thankfully proposed by Josh) was to be incremental. I was planning to incrementally go through the list of constructs that are either already in our current SOSA proposal or could be imagined to be in it and vote on them. Some, of course have implications, if we decide on owl:inverseOf in our next meeting, we will not be in RDFS entailment.
If we are already in OWL, then of course it would make sense to use owl:Class, although we do not have to. Therefore, again a vote on owl:Class thereafter.

I can think of the following list to vote on in our next meeting, incrementally. And we stopped at owl:inverseOf this meeting I just saw in the minutes.


-          rdfs:class

-          owl:inverseOf

-          owl:AnnotationProperty

-          owl:ObjectProperty

-          owl:Class

-          rdfs:domain and rdfs:range

-          rdfs:subClassOf

-          owl:Restriction

Please do think about these and if you think they should or should not be in the core or if there is anything else we desperately would need.

Kind regards,
Armin


From: Krzysztof Janowicz <jano@geog.ucsb.edu>
Date: Wednesday, 9 November 2016 at 10:01 am
To: Joshua Lieberman <jlieberman@tumblingwalls.com>, Simon Cox <Simon.Cox@csiro.au>, Kerry Taylor <kerry.taylor@anu.edu.au>, Armin Haller <armin.haller@anu.edu.au>
Cc: SDW WG Public List <public-sdw-wg@w3.org>
Subject: 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