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Re: Clarification on owl:real sought

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Thu, 08 Jan 2009 09:50:13 +0000
Message-ID: <4965CC55.9030302@hplb.hpl.hp.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: public-owl-dev@w3.org

Thanks Peter.

That helps a little.

What I'm trying to understand is what it means to "support" owl:real 
either for OWL 2 RL implementations or for RIF (though this is not an 
official RIF enquiry either).

For OWL 2 RL I can see that you can, for example, have a 
DatatypeProperty with range owl:real and that individual values within 
xsd:decimal and values within owl:rational would both be compatible with 
that range.

Would I be right in assuming that if owl:rational is dropped (which is a 
Feature At Risk, and I'd personally be happy to see it go) then there 
would be little point including owl:real in OWL 2 RL since all 
expressible numbers would then be within the value space of xsd:decimal?

Hewlett-Packard Limited
Registered Office: Cain Road, Bracknell, Berks RG12 1HN
Registered No: 690597 England

Peter F. Patel-Schneider wrote:
> [This is not an "official" response.  You might consider elevating this
> to a formal comment, perhaps because you want better explanation to show
> up in the documents.]
> owl:real is slightly strange as a datatype, in that it has uncountably
> many values in its value space.  This means that there is no way to have
> elements of its lexical space for all of its values.  (Well, we could, I
> suppose, but that might have some computational consequences for OWL,
> and even for storing and parsing OWL documents. :-) )
> I think that at one time, the OWL WG did discuss the idea of having
> lexical elements for certain interesting owl:real values (like pi or the
> square root of 2).  The current status, however, is that the lexical
> space for owl:real is empty.  (Remember that empty is a perfectly
> reasonable set!)
> This does not mean that elements of the value space of owl:real cannot
> be used in OWL ontologies.  For example, "1/3"^^owl:rational denotes an
> element of the value space of owl:real (just one that also an element of
> the value space of owl:rational).
> This illustrates a subtle difference between the treatment of datatypes
> in OWL and in XML Schema (but one that is described in the OWL
> documents).
> I hope that this answers your question.
> Peter F. Patel-Schneider
> From: Dave Reynolds <der@hplb.hpl.hp.com>
> Subject: Clarification on owl:real sought
> Date: Wed, 07 Jan 2009 11:39:17 +0000
>> [This is not a formal comment, just seeking understanding.]
>> In the OWL 2 Syntax specification [1] section 4 it states that every
>> datatype in the datatype map is described by a value space, a lexical
>> space and a facet space. 
>> In section 4.1 it lists owl:real as such a datatype but then says that
>> owl:real does not "directly provide any lexical values". Could someone
>> explain in what sense owl:real is a datatype if there are no lexical
>> values? 
>> Since owl:real is included in the OWL 2 RL profile that seems to imply
>> it is intended to be used in OWL 2 RL documents which would seem to
>> imply lexical values. 
>> Dave
>> [1] http://www.w3.org/TR/owl2-syntax/
>> [2] http://www.w3.org/TR/owl2-profiles/#Feature_Overview_3
>> -- Hewlett-Packard Limited
>> Registered Office: Cain Road, Bracknell, Berks RG12 1HN
>> Registered No: 690597 England
>> Ivan Herman wrote:
>>> The W3C OWL Working Group has just published seven drafts for OWL 2,
>>> including the structural specification, direct and RDF based semantics,
>>> serialization in RDF or in XML, Profiles, conformance and test cases. See
>>> http://www.w3.org/blog/SW/2008/10/10/seven_owl_2_drafts_published
>>> for more details and pointers to the documents themselves. The Working
>>> group seeks public feedback on the drafts; send your comments to
>>> public-owl-comments@w3.org. Please, send your comments until 2008-10-23.
>>> Cheers
>>> Ivan
Received on Thursday, 8 January 2009 09:51:35 UTC

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