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Re: Issue 80: terminology

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Wed, 25 Mar 2009 22:16:45 +0000
Message-ID: <49CAAD4D.2080706@hplb.hpl.hp.com>
To: Sandro Hawke <sandro@w3.org>
CC: RIF WG <public-rif-wg@w3.org>
Sandro Hawke wrote:
>> For OWL then they define xsd:dateTimeStamp to have a value space 
>> corresponding to a timeline instead of following the XML Schema 1.1 
>> structural model and so for OWL's definition identity and equality 
>> coincide again.
> 
> Actually, XSD put the timezone into the value space, and today OWL
> agreed to go along with that.  

Ugh. [I was going by the OWL wiki.]

> I don't like the outcome -- if a meeting
> ontology says a meeting can have one start time, and the same time is
> expressed twice, with different time zones, the ontology is inconsistant

Quite.

> -- but I don't see a way to fix it given how XSD and OWL each see the
> world, so I supported the decision.
> 
> My hope is that RIF is allowed more flexibility, and we can have
> identity, equality, and equivalence.  Or maybe we can settle on two of
> the three, but I'm pretty sure users need (and existing rule systems
> provide) Identity and Equivalence.

The existing XPath operators already in DTB give us equivalence for the 
the types that are of interest.

RIF "=" and the pred:literal-not-equal (as already defined in DTB) give 
us the identity and converse.

I think that's enough.

Dave

>      -  s
> 
>> So my contention is that the way literal-not-equal is defined in DTB at 
>> present (non-identity) corresponds to the equality notion in OWL for all 
>> the relevant datatypes and I keep my preference for options 2 or 1 [4].
>>
>> This contention is trivially true if we stick to XML Schema 1.0 because 
>> there is no distinction between equality and identity there. If we move 
>> to XML Schema 1.1 (is there a proposal to do this? I assume so) there 
>> are differences but the main problematic datatype is not included in OWL[5].
>>
>> Dave
>>
>> [1] http://www.w3.org/TR/xmlschema11-2/#value-space
>> "For purposes of this specification, the value spaces of primitive 
>> datatypes are disjoint, even in cases where the abstractions they 
>> represent might be thought of as having values in common."
>>
>> [2] http://www.w3.org/TR/xmlschema11-2/#value-space
>> "Note: In the prior version of this specification (1.0), equality was 
>> always identity.  This has been changed to permit the datatypes defined 
>> herein to more closely match the "real world" datatypes for which they 
>> are intended to be used as transmission formats."
>>
>> [3] I don't know what a good name for this is so I'm using "equivalence" 
>> for now. You could call it "programmatic equality" or "pragmatic 
>> equality" or something.
>>
>> [4] http://lists.w3.org/Archives/Public/public-rif-wg/2009Mar/0076.html
>>
>> [5] OK, that does leave the corner cases of float/double (-0 = +0, Nan 
>> != NaN) I haven't checked how OWL handle these. If those are the only 
>> differences then I personally don't care either way.
>> -- 
>> Hewlett-Packard Limited
>> Registered Office: Cain Road, Bracknell, Berks RG12 1HN
>> Registered No: 690597 England
>>
Received on Wednesday, 25 March 2009 22:17:30 GMT

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