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

From: Rob Shearer <rob.shearer@comlab.ox.ac.uk>
Date: Thu, 10 Jul 2008 11:24:51 +0100
Cc: Michael Smith <msmith@clarkparsia.com>
Message-Id: <7A397C76-3F78-498A-A2AA-5D4A8092E510@comlab.ox.ac.uk>
To: public-owl-wg@w3.org
> 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]).

I've just been looking through IEEE-754. Although it does allow for  
some differences in rounding implementations, it places (quite strict)  
limits on the possible error introduced. My understanding is that this  
means it is possible to encode any floating-point number in decimal to  
sufficient precision that any IEEE-754-compliant translation back to  
floating point results in exactly the same value.

Assuming that my understanding is correct, this means that it is  
perfectly safe to serialize floats as `xsd:float` within an OWL file  
without loss of precision: although there do exist `xsd:float` strings  
whose exact values are not precisely defined, users always have  
unambiguous representations available to them.

So I recommend sticking with the semantics for lexical representations  
defined in the XSchema spec.

-rob



Received on Thursday, 10 July 2008 10:25:29 UTC

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