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Re: ISSUE-126 (Revisit Datatypes): A new proposal for the real <-> float <-> double conundrum

From: Paul \ <paul@sparrow-hawk.org>
Date: Mon, 07 Jul 2008 10:38:36 -0600
Message-ID: <4872468C.6070607@sparrow-hawk.org>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
CC: Dave Peterson <davep@iit.edu>, Rob Shearer <rob.shearer@comlab.ox.ac.uk>, public-webont-comments@w3.org, public-owl-wg@w3.org, www-xml-schema-comments@w3.org

Alan Ruttenberg wrote:
> 
> I'm sorry for the overgeneralization and didn't mean to insult. It's 
> just that as much as I think about it, I can't understand the idea that 
> the value space of floats and the value space of decimal are disjoint. 
> Fundamentally these represent some of the same real numbers and this 
> isn't reflected in the spec. In addition, many numbers that can be 
> finitely expressed and be calculated with find no place in *any* of the 
> value spaces, e.g. 1/3. It is this sense of "mathematical" that I was 
> referring to.

The best explanation that I know of was written by Mark Reinhold, a 
member of the original schema WG (...and, if memory serves me, was a 
member of the team that wrote the Java floating-point spec).

During the development of the Schema 1.0 (i.e., a few years before we 
went to Rec) we had MANY discussions about the numeric types, and 
especially about float and double.  As part of that discussion, Mark 
wrote a note entitled "Floating-point datatypes are not real datatypes" 
[1] that goes into great detail on this point.  It also serves as a good 
entry point to the archives for the discussions the WG had on these issues.

pvb

[1] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/1999Oct/0025.html
Received on Tuesday, 8 July 2008 18:25:36 GMT

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