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Re: [xsl] Generating numbering for cross-references (LONG)

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[Peter Flynn]

> This has foxed numerous brains, including three of the co-authors of
> XSL and XPath. I hope it's not just my clumsy way of expressing it.
>
> In a typical research document, an author needs to make many
> cross-references.  XML provides ID and IDREF attributes for this
> purpose, and lots of DTDs are written to make use of them. I'm having
> a problem instatiating three classes of numeric cross-reference in
> XSLT, namely:
>
> a. Tables and figures, as in `See <ref to="foo"/>' where
>     you have <table id="foo"> or <figure id="foo">
>
[...]

> What I find unbelievable is that no-one has yet done this. It must be
> one of the most common requirements in document processing, and
> without it, XSLT simply cannot be used to reproduce simple numeric
> cross-references like "see Figure 16" or <plug>bibliographic
> references like Kay[23]</plug> :-)
>
> What have I missed?
>


You could approach this by creating a key that matches generate-id() of the
elements you are interested in (the ones with the ID attributes, I guess)
and returns the corresponding node.  Then you could create a variable
containing a list of those kind of nodes.  In processing, when you get to
that kind of element, identify it by generate-id(), use the key to get its
node or parent node or whatever, then call a named template on it to create
the reference number (table number, etc.) that you want, passing the node in
as a parameter.  When you do this, calling position() on the context node
will in fact give its position in the list of similar nodes, which is what
you want to construct your figure or section numbers.  You could do this on
a chapter-by-chapter basis if you wanted to.

You mentioned

> Youcannot reach over to the relevant part of the tree (by ID) and
> pluck a copy of a number which has not yet been generated.

But in fact the position of all the nodes is established before processing
of the stylesheet is started, when the document tree was build.  So you can
use that position anywhere in the stylesheet, if you if you don't think too
sequentially.

If you use a processor like Saxon or XALAN that lets you convert result tree
fragments to node-sets, you actually could build up your numbers and insert
them where you want.

Bear in mind that "before" in xslt processing generally means earlier in a
sequence of recursions, or earlier in a list of nodes, but not necessarily
"earlier" in the list of templates in the stylesheet.  You actually don't
know in what order the various templates might get processed.  You can only
know something about their precedence or dependency.

Another approach would be to use two passes - one stylesheet to insert the
numbers and one to identify where they should go.

I know this is fairly general, but you asked about a general topic.  I'm not
saying it would be easy, though.

Cheers,

Tom P


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