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Re: Errors in definition of XPath static context

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Wed, 19 Nov 2008 14:17:13 +0000
To: Norman Walsh <ndw@nwalsh.com>
Cc: public-xml-processing-model-comments@w3.org
Message-ID: <f5bzljvdcly.fsf@hildegard.inf.ed.ac.uk>

Hash: SHA1

Norman Walsh writes:

> I think we should say (perhaps "have said", since I'm not sure I want
> to try to fix this before we go to CR, though I'm game if everyone
> quickly signals assent) that those are the values in the *dynamic
> context*.

I'm for fixing this now.

> In the *static context*, we should say:
>   Statically known namespaces:
>      None
>   In-scope variables:
>      None
>   Base URI
>      Implementation defined.
> That's the only thing that makes sense, I think.

Hmm.  I have reviewed the XSLT 2.0 spec. to try to understand what the
difference between static and dynamic is supposed to be, and I'm not
convinced by your proposal.  My understanding, which could be wrong,
is that the _static_ context is what is the same for _every_
evaluation episode, whereas the _dynamic_ context is what may change
- From one episode to the next.  It follows that the static context is
for XSLT 2 is determined by the stylesheet context and the dynamic
context is determined by (things dependent on) the source document(s).

Why isn't the analogy, then, that for XProc the static context is
determined by the pipeline document context, and the dynamic context
the relevant input document?  If so, then what we have today is pretty
much correct, and your proposal is not needed.  The only thing I see
that needs to change is namespaces, which needs to be

  staticly known: from the containing element

  [oops -- Houston, we have a problem]: from p:namespaces

The split doesn't work, does it?  We are going to end up saying that
the static context isn't really static, because it has to be computed
at the same time that constructed XPaths are constructed. . .

In which case, the current document is entirely correct, as far as I
can see.  The properties you list don't _occur_ in the dynamic
context, after all.

Sigh.  We probably should talk about this tomorrow on the call.

- -- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Wednesday, 19 November 2008 14:17:51 UTC

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