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Re: Limitations of OWL 1.1 to RDF mapping

From: Pat Hayes <phayes@ihmc.us>
Date: Fri, 17 Nov 2006 13:30:52 -0600
Message-Id: <p06230900c183a2ff063d@[]>
To: Dave Reynolds <der@hplb.hpl.hp.com>
Cc: Bijan Parsia <bparsia@isr.umd.edu>, public-owl-dev@w3.org

>Bijan Parsia wrote:
>>On Nov 15, 2006, at 9:52 PM, Holger Knublauch wrote:
>>>The current OWL 1.1 Mapping to RDF Graphs draft [1] states
>>>"Not every OWL 1.1 ontology can be serialized in RDF. In 
>>>particular, ontologies using the following features of OWL 1.1 
>>>cannot be serialized:
>>These statements should be read as qualified with "under the 
>>current mapping".
>>>1. punning and
>>>2. annotations on axioms."
>>>Could anyone please clarify the implications of this statement. 
>>>Is the plan of the group to leave it like this, or are changes to 
>>>the OWL 1.1 spec underway to ensure that there will be a complete 
>>>mapping to RDF Graphs?  Or, will we see an "OWL 1.0.9" that will 
>>>be complete in RDF but with less features than 1.1?
>>The RDF mapping has lagged behind the others, but the plan is to 
>>extend the mapping to cover these cases.
>Presumably this will remain a purely syntactic mapping and the 
>comment in your "Next Steps for OWL" paper [1]:
>    "A triple syntax is being provided for OWL 1.1, syntactically
>    compatible with the triple syntax for OWL DL. However, for the above
>    reasons, this syntax could not be given a meaning compatible with the
>    RDF meaning for triples ..."
>will still apply?

Actually that statement is false. Such a syntax COULD be given a 
meaning compatible with the RDF semantics, and also (in a sense) with 
the OWL 1.1 semantics; but it would be a stronger assertion than the 
strict OWL 1.1 meaning. It is what you would get by merging the three 
OWL 1.1 notions of identity into a single meaning (equivalent then to 
owl:sameAs). Put another way, it is what you would get if OWL 1.1 
used punning on its own notion of identity in the same way as it uses 
it between classes/individuals/properties; which of course it does 
not. If it did, many more entailments would be supported; but all OWL 
1.1 entailments would be correct. Thus, an OWL 1.1 reasoner applied 
to the RDF triple syntax understood as legal RDF would be a valid but 
incomplete reasoner. Which is fine in my book: incomplete but valid 
reasoners are often very useful. I suspect that anyone who uses OWL 
1.1 with the intention of expressing genuine meta-modelling, instead 
of the rather weak imitation provided by the punning semantics,

BTW, the statement later in the paper,

"The possibility of continuing along this line [that is, the RDF 
style of semantics] in OWL 1.1 is called even more into question by 
the impossibility of extending it to Semantic Web languages with 
expressive power on a par with that of First-Order Logic"

is also false, or at best highly misleading. The ISO Common Logic 
draft standard (http://cl.tamu.edu/#cl) uses the same basic semantic 
construction as that used in RDF, i.e. unrestricted use of names, 
without punning, in a full first-order framework, in exact harmony 
with the semantics of RDF. Although ISO CL is unusually liberal in 
its syntax, the actual logic (without sequence markers) is 
first-order logic by all accepted semantic criteria (for example, it 
satisfies compactness and Skolem-Lowenheim), and can be processed 
using conventional first-order inference engines. This work has been 
publicly available for open comment now for over three years, and has 
been commented on by at least some of the authors of this paper. A 
more recent extension called IKL 
(http://www.ihmc.us/users/phayes/IKL/GUIDE/GUIDE.html ) continues 
(and utilizes) this semantic construction to extend the expressivity 
considerably beyond first-order logic, and is apparently known to at 
least some of the authors, as they have asked me about it personally. 
I can therefore only surmise that the reiteration of this falsehood 
in a recent publication is a deliberate attempt to mislead readers, 
in what appears to be a continuing and systematic attempt to diss 
RDF. I am at a loss to understand the motivation for this apparently 
self-destructive behavior.

Pat Hayes

>[1] http://owl-workshop.man.ac.uk/acceptedLong/submission_11.pdf

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Received on Friday, 17 November 2006 19:31:06 UTC

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