Re: [xml] Relative paths in XPointer

[Manuel González Castro <iinmgc00 ucv udc es>]

Daniel Veillard wrote:
> > On Wed, Feb 25, 2004 at 09:45:37PM +0100, Manuel González Castro wrote:
> > > Hi,
> > >
> > > The "XPointer xpointer() Scheme Working Draft"
> > > (http://www.w3.org/TR/xptr-xpointer/) says that the function "here()"
> > > can be used to point locations using relative paths. I'm trying to get
> > > it working with xmllint, but I'm getting errors whenever I use XInclude
> > > with XPointer relative paths.    
> > >
> > > I haven't seen any bug related to this error, and I think my xpointer
> > > expressions are correct. 
> > >
> > > So, does libxml support "here()" and other relative-path functions like
> > > "parent::*" inside xpointer expressions? 
> > >
> > > I'm using xmllint built on W2K from today CVS, and here are the
> > > testcases: 
> > >
> > > ---------------------------------------------------------------------
> > [...]
> > > ---------------------------------------------------------------------
> > > And this is the same with an xpointer relative path:
> > >
> > > D:\tests>type xpointer_relative.xml
> > >
> > > <a>
> > >   <b id="1"/>
> > >   <b id="2"/>
> > >   <c>
> > >     <xi:include
> > >   xpointer="xpointer(here()/parent::*/parent::*/b[ id='1'])"
> > > xmlns:xi="http://www.w3.org/2003/XInclude"/> </c> </a>
> > [...]
> > > Any hint?
> >
> >   You're playing with fire. The problem is what here() should be pointing
> > to. Assuming no XInclude processing and an evaluation of XPointer in the
> > document XPath data model of the given document, then here() should
> > probably 
> > point to the xi:include element.
> >   Now the problem is that you're running on an XIncluded document. As
> > part 
> > of the XInclude processing the xi:include element is discarded and
> > replaced 
> > by the evaluation of the include selection. And that selection start on
> > an 
> > element which doesn't exists anymore.

Can the processor evaluate the xpointer expression before replacing the xi:include with the result of the 
evaluation? This would solve the problem, at least in libxml. 

> >   I don't think it's a good idea to try to match XPointer here() and
> > XInclude processing, since basically there is a deep conflict between
> > both, and I doubt you will end up with a reliable solution in any case.

Anyway, my problem is solved (in fact, I had no problem at all). I was trying to use relative paths in 
xpointer when including a fragment of the self document because I was afraid of problems with absolute paths 
when chaining inclusions, but I've tested it and there is no problem.

If anybody is interested:

A document including a fragment of itself with an absolute path:

D:\tests>type included.xml

<model>
  <item id="1">I want this</item>
  <item id="2"/>
  <group>
    <xi:include xpointer="xpointer(/model/item[ id='1'])" xmlns:xi="http://www.w3.org/2003/XInclude"/>
  </group>
</model>

Resolve includes, everything is fine:

D:\tests>xmllint --xinclude included.xml
<?xml version="1.0"?>
<model>
  <item id="1">I want this</item>
  <item id="2"/>
  <group>
    <item id="1">I want this</item>
  </group>
</model>

Now include the first doc in a second one, which has an element that matches the absolute path given in the 
first doc (/model/item[ id='1']):

D:\tests>type includer.xml

<model>
  <item id="1">I don't want this</item>
  <item id="2"/>
  <submodel>
    <xi:include href="included.xml" xmlns:xi="http://www.w3.org/2003/XInclude"/>
  </submodel>
</model>

Resolve includes and everything is fine again:

D:\tests>xmllint --xinclude includer.xml
<?xml version="1.0"?>
<model>
  <item id="1">I don't want this</item>
  <item id="2"/>
  <submodel>
    <model>
  <item id="1">I want this</item>
  <item id="2"/>
  <group>
    <item id="1">I want this</item>
  </group>
</model>
  </submodel>
</model>

Great library!

Thanks,
Manuel