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Re: Clarification on owl:real sought

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Thu, 08 Jan 2009 14:29:02 +0000
Message-ID: <49660DAE.6080001@hplb.hpl.hp.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: public-owl-dev@w3.org

Peter F. Patel-Schneider wrote:
> Your analysis is correct.
> Supporting owl:realPlus (to pick a slightly more interesting example)
> means something like allowing ontologies like: 
> DataProperty(ex:wealth)
> SubClassOf(ex:Person AllValuesFrom(ex:wealth owl:real))

You mean owl:realPlus there right?

> ClassAssertion(ex:Person ex:Steve)
> ClassAssertion(ex:Person ex:Bill)
> PropertyAssertion(ex:wealth ex:Brian "+10000000000000000000"^^xsd:integer)
> PropertyAssertion(ex:wealth ex:Bill "+INF"^^xsd:float)
> In the absence of real constants, it is indeed the case that owl:real is
> going to act very much like owl:rational, as far as OWL itself is
> concerned.  If owl:rational is removed then owl:real is going to act
> very much like xsd:decimal.
> Perhaps the main reason for owl:rational and owl:real is to allow for
> extensions of OWL that provide relationships between values.

Got it, that makes sense.
Thanks for your help.


> peter
> From: Dave Reynolds <der@hplb.hpl.hp.com>
> Subject: Re: Clarification on owl:real sought
> Date: Thu, 08 Jan 2009 09:50:13 +0000
>> 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?
>> Dave
>> -- 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 14:30:27 UTC

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