RE: would a semantics by any other name look as formal?

Hi Peter!

>-----Original Message-----
>From: Peter F. Patel-Schneider [mailto:pfps@research.bell-labs.com]
>Sent: Saturday, March 14, 2009 12:52 AM
>To: Michael Schneider
>Cc: public-owl-wg@w3.org
>Subject: would a semantics by any other name look as formal?
>
>EXECUTIVE SUMMARY:
>
>  The RDF-Based Semantics document should use "RDF-based semantics"
>  uniformly when talking about the semantics that it defines.

Yes, this is actually what I plan to do. The Document Overview calls it that way throughout the document, and therefore the RDF Based Semantics document should also call it this way, to avoid confusion. I have an ednote on this at the beginning of the document, and will change this as soon as I consider the document to be complete in all other aspects (probably next week). 

[...]

>> With this in mind, in the RDF-Based Semantics document I have used the
>>term "OWL 2 Full" exclusively to mean the /semantics/.
>
>I do not believe that "OWL Full" ever meant just the semantics.  My
>recollection is that "OWL Full" was always the combination of syntax and
>semantics.  

Yes, I think so, too. I was never very happy with using "OWL 2 Full" for the semantics solely, but did not find a clear hint in the OWL 1 spec that could tell me how it was meant. Usages of "OWL Full" always sounded "very semantic" to me. I never came to the idea, though, that someone might think of OWL Full as only a syntax.

Skimming through your text fragments below, I can see a few relevant points:

"""
Eliminating these limitations results in the full OWL language, 
called OWL Full, which has the same syntax as RDF.
"""

Well, OWL Full is called a language here, but this might be seen as a vague statement. In any case, it is said that OWL Full /has/ a syntax. It's not said that OWL Full /is/ a syntax. So, according to this text, "OWL Full" can either mean the semantics or the whole langugage here.

On the other hand:

"""
This document contains two formal semantics for OWL. 
[...]
The other, defined in Section 5, is a vocabulary extension of 
the RDF semantics [RDF Semantics] that provides semantics for OWL 
ontologies in the form of RDF graphs. Two versions of this second 
semantics are provided, 
[...]
and one that can be used in cases where classes
need to be treated as individuals or other situations that cannot be
handled in the abstract syntax (and is thus a semantics for OWL
Full).
"""

This time it is said that the "other" semantics is a semantics /for/ OWL Full. It's /not/ said that OWL Full /is/ a semantics. So, according to this text, "OWL Full" can either mean the syntax or the whole language here.

Taken both texts together, the only possible consistent result is "whole language". :-)

But let's look at a few other examples:

>Appendix A contains a proof that the direct and RDFS-compatible
>semantics have the same consequences on OWL ontologies that correspond
>to abstract OWL ontologies that separate OWL individuals, OWL classes,
>OWL properties, and the RDF, RDFS, and OWL structural
>vocabulary. Appendix A also contains the sketch of a proof that the
>entailments in the RDFS-compatible semantics for OWL Full include all
>the entailments in the RDFS-compatible semantics for OWL DL. Finally a
>few examples of the various concepts defined in the document are
>presented in Appendix B.

I think, from this text it becomes pretty clear that there was always a clear distinction between the two semantics and the two things that have been called "OWL XX". Such a distinction is what I prefer for the successor of OWL Full, either.

>There are two different styles of using OWL. In the more free-wheeling
>style, called OWL Full, the three parts of the OWL universe are
>identified with their RDF counterparts, namely the class extensions of
>rdfs:Resource, rdfs:Class, and rdf:Property. 
[...]
>Both styles of OWL provide entailments

So we read: "In OWL Full, parts of the OWL universe are identified..." and "OWL Full provides entailments". I think, this clearly cancels out any idea that OWL 1 Full could have ever been meant as a syntax (RDF Graphs) only. 

And so on...

So, what I believe to see from the texts is just what you say in the beginning of your mail: That OWL Full was meant to be the language consisting of a syntax and a semantics. Neither semantics alone, nor syntax alone. 

>I expect that it is best not to conflate OWL 2 Full with the RDF-Based
>Semantics.  The Direct Semantics document is careful not to make this
>conflation, and uses "Direct Semantics" or some variant thereof when
>referring to its semantics.  I suggest that the RDF-Based Semantics
>document go this way, and use "RDF-Based Semantics" when referring to
>the semantics it defines.

Fully agreed!

I think that it might even be possible to refrain from ever talking about the "OWL 2 Full" language in the whole document, but I have to check, when later working through the document.

There is just a little point to be considered here, just for the case that you would like to see the term "OWL 2 Full" completely vanishing from the document: The old OWL 1 spec introduced terms such as "OWL Full interpretation" and "OWL Full entails". Obviously, I have "reused" these terms in the RDF-Based Semantics spec ("OWL 2 Full interpretation", and the like). What about these terms now? I would be pretty reluctant to deviate in the nomenclature from the old spec in this respect. A few simple Google queries show me that the original terms have already been used outside the old spec.

Best,
Michael

--
Dipl.-Inform. Michael Schneider
Research Scientist, Dept. Information Process Engineering (IPE)
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