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Re: Review of XSD Datatypes 1.1 Changes

From: Sandro Hawke <sandro@w3.org>
Date: Wed, 08 Feb 2012 08:43:36 -0500
To: Pat Hayes <phayes@ihmc.us>
Cc: Alex Hall <alexhall@revelytix.com>, RDF WG <public-rdf-wg@w3.org>
Message-ID: <1328708616.16744.50.camel@waldron>
On Fri, 2012-02-03 at 23:49 -0800, Pat Hayes wrote:
> On Feb 3, 2012, at 2:27 PM, Alex Hall wrote:
> 
> > On Fri, Feb 3, 2012 at 3:49 PM, Pat Hayes <phayes@ihmc.us> wrote:
> > 
> > On Feb 2, 2012, at 2:08 PM, Alex Hall wrote:
> > 
> > > Per ACTION-136 - Review changes in W3C XML Schema Definition Language (XSD) -- http://www.w3.org/TR/2012/PR-xmlschema11-2-20120119/#changes
> > >
> > > I've completed my review of the changes in XSD Datatypes 1.1. Rather than go through the exhaustive list of changes, I'll summarize the areas that I think are relevant to RDF:
> > >
> > > 1. Datatype definitions, including definitions of lexical spaces, value spaces, L2V mappings, and canonical mappings, underwent a thorough revision. This is a good thing, because the new definitions are much more precisely stated and leave less room for confusion. In general, RDF defers to XSD for datatype definitions so I don't think any action on our part is required here in terms of the RDF specs. However, implementors of XSD datatype processing in RDF will want to review these changes so we might want to call their attention to them. I did verify that the short-form literal definitions in Turtle for boolean, double, decimal, and integer are still valid subsets of the respective lexical spaces in XSD 1.1.
> > >
> > > 2. XSD 1.1 distinguishes between the identity of values and the (numeric) equality of values.
> 
> ....
> 
> > > To avoid confusion, it might be worth noting this distinction in the section on datatype entailment and explicitly stating that datatype entailment deals with identity and not equality, if that is indeed our position. [For SPARQL, pattern matching deals with identity and the '=' operator deals with equality.
> > 
> > Is that a previous decision, or do you just presume that it must work this way?
> > 
> > This is based on RDF Semantics section 1.4 (http://www.w3.org/TR/rdf-mt/#gddenot):
> > 
> > "In this table, and throughout this document, the equality sign = indicates identity"
> 
> Sigh. That however was written using English as it was before XSD got to it, in the good old days when "identity" and "equality" were, um, identical. So while indeed it does mean to refer to identity, it did not mean to contrast this with equality. It uses the sign "=" to refer to identity, for example. 
> 
> So, after a brief period of mental anguish, I am inclined to say that our best response to this is to insert some explanatory prose into the semantics document which emphasises that RDF semantics recognizes, and is based upon, the notion of logical identity, and when XSD defines an 'equality' which differs from identity, that is not what we are talking about. 

I don't claim to understand all this, and that's probably okay.  The way
I make sense of XSD, when I have to, is to translate what they are
saying into programmer-speak (not math-speak).  The value spaces sound
mathematical, but integer 3 and floating point 3 are not identical
because (not surprisingly) they are implemented in all practical systems
using different bit patterns.   I wish the XSD spec would stick to
programmer-speak, but I guess that's seen as too constraining on
implementations.

  -- Sandro

> Pat
> 
> 
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Received on Wednesday, 8 February 2012 13:45:51 UTC

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