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Re: A possible structure of the datatype system for OWL 2 (related to ISSUE-126)

From: Michael Smith <msmith@clarkparsia.com>
Date: Wed, 09 Jul 2008 13:10:47 +0000
To: Boris Motik <boris.motik@comlab.ox.ac.uk>
Cc: 'OWL Working Group WG' <public-owl-wg@w3.org>
Message-Id: <1215609047.23047.26.camel@msmith-laptop-wired.int.clarkparsia.com>

On Tue, 2008-07-08 at 17:16 +0100, Boris Motik wrote:

> - "aaEbb"^^xsd:float - all such constants save for NaN and +-inf are to be interpreted as elements of owl:number

I continue to find this problematic, as it ignores the discussion of
why floats are not reals (I found [1] quite helpful).

Further, I have concern that because the lexical space allows arbitrary
precision and due to alternative, inconsistent rounding implementations
(permitted by XSD 1.1 [2], see 3.3.5.2) the lexical to value-space
mapping could differ between implementations. Thus, two reasoners with
xsd conformant lexical to value mapping algorithms could correctly
produce different entailments.  (I don't have access to IEEE-754 to look
into the details here, I'm basing my statements on [2]).


> The set of constants is chosen such that implementations don't need to support numbers with arbitrary precision, which might be
> quite cumbersome. In fact, implementations are only required to support 32 bit integers and single precision floating point numbers.
> There are efficient ways to represent these on virtually all systems.

I agree that requiring arbitrary precision for conformance may be
placing the bar too high.

I note that XSD specifies a number of digits for minimally conformant
reasoners [3], [4].  Perhaps we could adopt a similar approach to
conformance.

-- 
Mike Smith

Clark & Parsia


[1] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/1999Oct/0025.html
[2] http://www.w3.org/TR/xmlschema11-2/#float
[3] http://www.w3.org/TR/xmlschema-2/#decimal
[4] http://www.w3.org/TR/xmlschema11-2/#partial-implementation
Received on Wednesday, 9 July 2008 13:22:49 UTC

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