Re: [docbook-apps] Xmllint error

[Daniel Veillard <veillard@redhat.com>]

On Tue, Oct 07, 2003 at 11:31:23AM +0200, Kenneth Johansson wrote:
> Hi,
> 
> When compiling my modular docbook file I get this xmllint error message.
> What am I doing wrong?

  Nothing. It's a problem between DocBook DTD and XInclude.

> $ xmllint --xinclude --postvalid IDS5webUGbook.xml > out.xml
> IDS5web/1_Introduction/chapter_all_introduction.xml:3: No declaration for
> attribute base of element chapter .

  Since there seems to be some confusion about the exact problem
let me explain a bit what's going on:
   
   xmllint --xinclude --postvalid does the following:
    1/ parse the document, load the DTD but does not validate while
       parsing
    2/ apply the XInclude processing which will recursively traverse
       the document(s) and include the new informations gathered from
       new documents (or text source)
    3/ validate the resulting in-memory tree with the DTD from the
       "main" document.

 So now what's this base attribute, where does it come from, and why:
    1/ it's actually xml:base , an attribute which allows to set the base
       for URI-Reference computation done in the subtree of the document.
    2/ it is added by XInclude processing to not break references done
       from included document. Say that main.xml includes subdir/chapter.xml
       and that subdir/chapter.xml references an image img.png .
       The rules for references expects the image to be found in subdir/img.png
    3/ XInclude has no notion of what in teh included document might
       be a reference. So to preserve the linking functionality it mandates
       to add an xml:base="subdir/chapter.xml" at the point where the
       inclusion occured si that the reference from the resulting document
       to the image be preserved.

 The consequence is:
   - there is nothing to prevent this from an authoring point of view
     except keeping all the included fragment in the same directory
     as the main document
   - the only solution is to get Docbook XML DTD to allow xml:base as
     a #IMPLIED attributes on the elements which are likely to be top of
     inserted documents. I though this was agreed upon but didn't checked
     the progress, Norm or Paul can probably tell us more about this.

 At the moment you can safely ignore any [xml:]base attribute error message
resulting from postvalid after XInclude processing.

Daniel



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