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RE: question about lexical and value spaces

From: <noah_mendelsohn@us.ibm.com>
Date: Thu, 17 Jan 2008 20:24:39 -0500
To: "Michael Kay" <mike@saxonica.com>
Cc: "'Peter F. Patel-Schneider'" <pfps@research.bell-labs.com>, www-xml-schema-comments@w3.org
Message-ID: <OF6B6C6649.3475EAA9-ON852573D4.0007369D-852573D4.0007AD4B@lotus.com>

Michael Kay writes:

> There is intense debate about whether "ineffable values" (values with no
> lexical representation) should be considered as being within the value 
> or not. 

Really?  I thought we were always clear that if there was no lexical form, 
there was no value.  For example, I thought it was pretty clear that if 
you used a pattern facet to restrict away all the lexical forms ending in 
the digit 4 in a type derived from xs:integer, then the numbers 4, 14 and 
so on were in fact not in the value space of the type.  Paul Biron and I 
tend to recall often the discussion we had many years ago in line waiting 
for dinner at a restaurant near the first New Orleans meeting at which we 
pointed out how impractically hard it would be to enforce such things in 
systems that in fact allow the values to be manipulated directly.  If you 
have an API that purports to establish some new value of a datatype, it 
can be very difficult to test whether there does or doesn't exist at least 
one lexical form for it in the face of complex patterns.  Still, the 
datatypes were focussed mainly on validation, and there is something very 
appealing about being able to say that every value has at least one 
serialization.  I was not aware that there was any serious consideration 
of changing this. 

Suggestion:  can we take this discussion to the schemas IG list where more 
WG members will see it?  As far as I know the comments list is tracked 
very carefully for picking up new issues and bug reports, but it is not 
necessarily subscribed by all members of the working group.


Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
Received on Friday, 18 January 2008 01:24:13 UTC

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