Re: [xml] XPath question

[Daniel Veillard <veillard redhat com>]

On Wed, Aug 04, 2004 at 01:26:01PM -0400, Jesse Pelton wrote:
> I think the operative thing here is, "Assuming foo is mapped to your
> namespace name in the XPath context."  I probably should have mentioned
> in my posting that I came up with my expression to deal with
> environments where there was no mechanism to establish such mappings
> other than by including a namespace prefix in the instance document.  As
> far as I can see, XPath 1.0 does not specify such a mechanism, but

  http://www.w3.org/TR/xpath#section-Conformance

 "XPath is intended primarily as a component that can be used by other
  specifications. Therefore, XPath relies on specifications that use XPath
  (such as [XPointer] and [XSLT]) to specify criteria for conformance of
  implementations of XPath and does not define any conformance criteria
  for independent implementations of XPath."

 In a nutshell, XPath was not supposed to be used in isolation. It was left
to the other specifications using it (XSLT and XPointer) to state how
they allowed to set namespace mapping in the evaluation context. Both XSLT
and XPointer do, that mechanism is expected to be provided but XPath doesn't
define how, precisely because it was designed to be embedded.

> libxml does, of course.  So, my posting was not completely relevant to
> this list.  I was excited to find a solution (even if inefficient) to a
> real problem that I had; I hope I can be forgiven for choosing the wrong
> forum to share it!

  I would expect *any* XPath implementation to provide the mapping
between prefixes and namespace name as the mapping is part of the
XPath evaluation context -last item in the bulleted list:
  http://www.w3.org/TR/xpath#section-Introduction

It is somewhat mandatory since it is needed to parse the XPath expressions.

It is not a matter of relevance or wrong forum. Let's say I got irritated
by the fact you pointed as wrong a correct and clean solution and suggested
instead a relatively cumbersome and not readable one. Anybody can misunderstand
those specs, they are complex it happens all the time, not a big deal,
but I have to point out what the spec really states and mean.

Daniel


-- 
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veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
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