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Re: Some basic questions about OWL-Full

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Mon, 22 Oct 2007 22:12:00 -0400
Message-Id: <CDBB7854-EB71-458A-BBCE-24B75277143C@gmail.com>
Cc: Michael Schneider <schneid@fzi.de>, Owl Dev <public-owl-dev@w3.org>
To: Pat Hayes <phayes@ihmc.us>, "Peter F. Patel-Schneider" <pfps@RESEARCH.BELL-LABS.COM>

One point I have been confused about is the interplay between the  
abstract syntax and OWL Full. I was under the impression that even  
OWL full needs to be able to be expressed in the abstract syntax. But  
the abstract syntax is such only trees of anonymous individuals are  
possible to express, but not cycles. However, a cycle of blank nodes  
*is* able to be expressed in RDF (= OWL Full?)

-Alan

On Oct 22, 2007, at 4:56 PM, Pat Hayes wrote:

>
>> Hi!
>>
>> OWL-Full has ever been a complete mystery to me, ....
>
> ....
>
> It is really quite simple. Take OWL/RDF and think of it as an RDF  
> 'extension'. The RDF and OWL vocabulary (and associated  
> constructions) have to satisfy all the RDF and OWL semantic  
> conditions stated in the specs. OK, that is all there is to OWL- 
> Full. It does not constrain the form of an RDF graph and it does  
> not impose any syntactic conditions on how the OWL vocabulary is  
> used. It does however insist that however it gets used, the  
> meanings of this vocabulary must satisfy the semantic conditions  
> imposed upon it. It does not recognize distinctions like that  
> between class/individual/property and between object/datatype  
> classes or properties. In this, it follows RDF and RDFS, since the  
> RDF semantics (and the ISO Common Logic semantics) allows any name  
> to denote any 'type' of thing, or indeed to denote several of them  
> at once.
>
> Notice that I did not mention the OWL 'abstract syntax' at all. At  
> the insistence of the Manchester members of the working group, the  
> OWL spec is stated with the abstract syntax as primary, and the  
> mapping into RDF described almost as an afterthought, a  
> 'projection' from the real language to an alien notation. This is  
> not the right way to think about OWL-Full, and not how it was  
> conceived. It is designed to fit into a picture where RDF is  
> primary and more complex languages are created by adding special  
> vocabularies to RDF with associated semantic conditions imposed on  
> their meanings. This is how RDFS is described, for example, and OWL- 
> Full is in the same tradition. In fact, OWL-Full was created in  
> response to a claim made and reiterated several times in the WG,  
> that a language as complex as OWL was inherently incompatible with  
> RDF, and that the RDF encoding therefore should be abandoned.  
> Echoes of that debate can still be heard in some parts of the world.
>
> This gives a rather different perspective to several contentious  
> issues. From the Manchester view, some parts of OWL/RDF are genuine  
> OWL assertions, while others are simply artifacts of the syntactic  
> embedding from the abstract syntax. There is absolutely no such  
> distinction in OWL-Full. Again, some RDF graphs are considered by  
> DL thinkers to be 'assertions about the logical syntax' or to  
> 'change the meaning of the logical syntax'; but neither claim is  
> true when seen from the perspective of OWL Full itself. No OWL/RDF  
> assertion can change the semantics of, say, rdf:type or of  
> owl:Restriction, as these semantics are written into the semantic  
> specification.
>
> What one can do is *add to* the meaning of such terms by imposing  
> extra, axiomatically stated, conditions, ie by writing axioms. This  
> can, in some cases, have some peculiar consequences; but they are  
> not incoherent or illogical, just, well, peculiar. (OWL-DL also  
> allows for some very peculiar conclusions arising from its  
> insistence on extensional readings of classes and properties.) But  
> it also allows for some very useful generalizations which have  
> potential uses in real ontologies.
>
> Anyway, I hope this helps.
>
> Pat
> -- 
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Received on Tuesday, 23 October 2007 02:12:14 GMT

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