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RE: ISSUE-126 (Revisit Datatypes): The list of normative datatypes should be revisited

From: Michael Smith <msmith@clarkparsia.com>
Date: Thu, 19 Jun 2008 11:09:35 -0400
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
Cc: 'Alan Ruttenberg' <alanruttenberg@gmail.com>, 'OWL Working Group WG' <public-owl-wg@w3.org>
Message-Id: <1213888175.6245.72.camel@msmith-laptop-wired.int.clarkparsia.com>

On Thu, 2008-06-19 at 08:49 +0100, Boris Motik wrote:

> > I also have a rather basic question about the datatype formulation in
> > the OWL semantics. Specifically, although I believe the xsd datatypes
> > are considered disjoint, their value spaces intersect, i.e. the value
> > space of positive integers intersects the value space of xsd:float.
> > Is that correct?
> 
> Yes; hence, the datatypes that we have in the spec are not disjoint.
> 
> Please don't get confused by the fact that we have formalized datatypes as being disjoint in our paper. This is just for convenience
> of presentation: we have assumed that we have one numeric datatype and that different subsets (such as integers) are modeled as
> facets. We are not proposing to do this in the OWL 2 spec; this has been used in the paper merely as a convenience because it
> allowed us to compartmentalize all problems related to numbers to a single datatype.

There are existing implementations based on disjointness of primitive
datatypes (Pellet, Jena, etc.) and in [1] the "best practice" advice
encourages this assumption.  It includes this specific example

        eg:JeremyCarroll eg:ageInYears "40"^^xsd:integer .
        
        does not entail 
        
        eg:JeremyCarroll eg:ageInYears "40"^^xsd:float .

So, allowing xsd:float and xsd:integer to have intersecting value spaces
is a change from existing behavior (i.e., a cost to users) and a cost to
implementers that implemented datatype support in the past.

On the other hand, I'm not sure I understand the benefit of allowing the
value spaces to intersect.  I think you're advocating it so that an
implementation is permitted to treat xsd:float and xsd:double as
synonyms of owl:real.  Is that correct or was there something more?

-- 
Mike Smith

Clark & Parsia

[1] http://www.w3.org/TR/swbp-xsch-datatypes/#sec-values
Received on Thursday, 19 June 2008 15:10:17 GMT

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