Re: [xsl] Check for duplicate @id's - collection()

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2008-07-19 11:28 -0400, Philip Vallone wrote:
> I have a project were I take about 800 files and transform them into one .fo
> document (create a pdf). The files are authored independent of each other
> (stand alone) which are validated against a schema (independently). If there
> is a duplicate @id attribute, the validator will tell me. However, the @ids
> need to be unique across all files processed by the collection function. If
> they are not, my resulting .fo will have duplicate @ids, which cause FOP to
> halt.

This is the use case for generate-id() ... in my XSL classes I take 
the students through the two steps of ensuring unique identifiers in 
aggregating XML source documents to a single XSL-FO result document:

   Assuming the current node is the element with the @id attribute, the
   unique anchor in the FO tree is created using something along the lines
   of:

      <block id="{generate-id(.)}">

   Assuming you are at the element that is making the reference with @idref
   and you have a DTD declaration for the ID property of the target element,
   the link is created using:

      <basic-link internal-destination="{generate-id(id(@idref))}">

   ... or you can just move your context to the element with the @id
   attribute and do:

      <basic-link internal-destination="{generate-id(.)}">

> I am looking for a way to (query or xslt 2.0) to check for duplicate @id's
> values across all files with the collection function. This would be a
> pre-production check.

Not needed if you choose to use generate-id() ... it is specified to 
guarantee uniqueness across all nodes when it is called for any node 
in the node tree, and within one run of the stylesheet you always get 
the same value returned for any given node.

It is an opaque value, alpha-numeric, that you use without analyzing 
its value because every processor will give you something different 
... but you can add your own ".","-" or "_" character to it if you 
need to make multiple unique anchors for one node.

The value is not guaranteed to be the same the next time you run the 
stylesheet on the node tree, even if the node tree is unchanged.  The 
value cannot be reliably sorted or relied on for any purpose other 
than being unique.

By using generate-id() you never need to worry which values are being 
used by your authors, provided within each XML file they are being 
used properly.

I hope this helps.

. . . . . . . . . .  Ken

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