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Re: Some basic questions about OWL-Full

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 22 Oct 2007 22:03:34 -0500
Message-Id: <p0623090dc34312bb879d@[192.168.1.2]>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
Cc: Michael Schneider <schneid@fzi.de>, Owl Dev <public-owl-dev@w3.org>, "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.

No. The AS embodies the 'subset of FOL' view of OWL-DL, which is of 
course the conventional way to think about DLs themselves. But as I 
said, none of this is central to the OWL-Full view of OWL, which 
treats it simply as an RDF extension. The only syntax relevant to 
OWL-Full is RDF 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?)

For example (and there are many others).

Pat

>
>-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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IHMC		(850)434 8903 or (650)494 3973   home
40 South Alcaniz St.	(850)202 4416   office
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FL 32502			(850)291 0667    cell
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Received on Tuesday, 23 October 2007 03:03:53 GMT

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