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

From: Krzysztof Janowicz <janowicz@ucsb.edu>
Date: Wed, 9 Nov 2016 08:33:56 -0800
To: Armin Haller <armin.haller@anu.edu.au>, Krzysztof Janowicz <jano@geog.ucsb.edu>, Joshua Lieberman <jlieberman@tumblingwalls.com>, Simon Cox <Simon.Cox@csiro.au>, Kerry Taylor <kerry.taylor@anu.edu.au>
Cc: SDW WG Public List <public-sdw-wg@w3.org>
Message-ID: <30da4481-0b52-3226-d38a-2a8499d2d59b@ucsb.edu>

Thanks Armin.

> 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.

I see your point but I must say that it is opposed to any ontology 
engineering methodology I know.

What (almost all of) these methods tell us, is to first model with 
pen&paper or using concept maps. Only after this step one should try to 
formalize the desired knowledge using a particular knowledge 
representation language. The reason for this is that the choice of 
formal modeling paradigm and language restricts what one can state and 
how to do this. Thus, ideally, one would first specify the core 
conceptualizations of the domain and then try to figure out how to best 
capture them in a formal language.

I find the idea of starting with particular language elements first a 
bit odd. This is like instead of saying "I need an ontology about 
elections and would like to state that there is no such person that has 
voted as democrat and republican at the same time" to which we would 
answer "okay, lets declare them to be disjoint classes", one would say 
"hey, I would like to have a disjointness axiom in my ontology" and one 
would say "so maybe your ontology should be about elections".

I think we should first make sure we understand what we want to have in 
SOSA-core and next decide on whether there are any specific KR/KL 
choices we need to make. Lets not be driven by technology here but by 
semantics. Nobody will freak out if we use OWL instead of RDFS, but 
people will freak out if our ontology becomes less useful than it could 
be. Just as a side node, (old) SSN is in OWL. SOSA-Core is about core 
*concepts* of SSN, not core knowledge representation language fragments.


On 11/08/2016 03:20 PM, Armin Haller wrote:
> 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

Krzysztof Janowicz

Geography Department, University of California, Santa Barbara
4830 Ellison Hall, Santa Barbara, CA 93106-4060

Email: jano@geog.ucsb.edu
Webpage: http://geog.ucsb.edu/~jano/
Semantic Web Journal: http://www.semantic-web-journal.net
Received on Wednesday, 9 November 2016 16:34:32 UTC

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