In QT we have to consider a query or transformation as a whole. Documents
are annotated with types, and we need to have confidence that when we see a
type annotation, we know what type it refers to. The processing model
assumes that types can be identified by a QName. For this to work, we can't
have two different types with the same QName within the scope of a query or
transformation (in the XQuery case, this scope is an entire database...).

This is something of a pain, because it means you can't use XSLT to
transform from one version of a schema to another version of the same schema
if it uses the same namespace. Clearly we need a versioning story, as you
have often said yourself...

But it also affects redefine. If I load two documents as inputs to a query
or transformation, one validated using schema A, and the other using schema
R which redefines schema A, then I've got two types with the same name, and
everything (in particular, QT type checking) breaks.

Michael Kay
 

> -----Original Message-----
> From: Henry S. Thompson [mailto:ht@i...] 
> Sent: 17 August 2005 14:01
> To: Michael Kay
> Cc: 'Kasimier Buchcik'; 'XML-SCHEMA'
> Subject: Re: implementing redefinitions
> 
> -----BEGIN PGP SIGNED MESSAGE-----
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> 
> Michael Kay" writes:
> 
> > I'm struggling with this a bit in Saxon. I think the rule I 
> have to adopt is
> > that once a schema component has been used for validating 
> documents that
> > exist in the current "environment" (that is, whose PSVIs I 
> can reach),
> > redefinition of that schema component is banned.
> 
> On an episode-by-episode basis, this makes sense to me, and I think is
> covered at least in many cases by the "no new namespaces once we
> start" provision.
> 
> But across multiple episodes, I don't think the spec. licenses this --
> each episode should be treated completely independently.
> 
> So, the obvious question -- how can their be more than one document in
> the "current 'environment'"?
> 
> ht
> - -- 
>  Henry S. Thompson, HCRC Language Technology Group, 
> University of Edinburgh
>                      Half-time member of W3C Team
>     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 
> 131 650-4440
>             Fax: (44) 131 650-4587, e-mail: ht@i...
>                    URL: http://www.ltg.ed.ac.uk/~ht/
> [mail really from me _always_ has this .sig -- mail without 
> it is forged spam]
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