Re: [xml] XPath expression portability framework dependance

[Daniel Veillard <veillard redhat com>]

On Thu, Dec 26, 2002 at 03:57:27PM +0100, Stefano Debenedetti wrote:
> Daniel Veillard wrote:
> > Registering the namespace in the XPath evaluation context is less
> > portable but easier to understand. Note that the XPath specification
> > was not done with the expectation it would be used standalone but
> > always in a framework (XSLT and XPointer originally) which were 
> > defining the mechanism for the context initialization.
>
> Now, this seems to me a very interesting topic because I have been 
> trying to use the current() XSLT function in a standalone XPath query 
> and I couldn't find a way to do that using the python bindings of 
> libxml2 +libxslt but both xalan and saxon XPath implementations support 
> it by default even in standalone XPath queries.

  current() being an XSLT function it is not implemented in
the XPath core. Enough people complain that libxml2 is too big
compared to expat (grumpf ...)...

> Is there a way to do use the current() function in a standalone XPath 
> using libxml2+libxslt too? Is it more standards-compliant than the 
> solution taken by xalan&saxon? Or is it that the framework-dependance of 
>   XPath means that there is not a standard way to do that?

  Standard, no. You can register functions at the C level to the
XPath core, that exactly what the libxslt library does when it is
initialized. I think this should be doable at the python level too
by calling the XSLT initialization function.

> I am interested because this seems like potential XPath portability 
> problems between, say, an XForms implementation written in java and one 
> written in python....

  It will always be a portability problem, because the API are not
standardized (and should not IMHO, the closest is the XPath DOM3 module).
My stand on not standardizing the APIs is that usually it ended up with
really bad ones, tied to a language, and in general unusable from C.

Daniel

-- 
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