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

Subject: RE: [xsl] Check for duplicate @id's - collection()
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Sat, 19 Jul 2008 12:24:20 -0400
At 2008-07-19 12:09 -0400, Philip Vallone wrote:
This is a great idea which I currently use the following template for:

<xsl:template name="get-mandatory-id">
                <xsl:param name="id-val"/>
                        <xsl:when test="string-length($id-val) &gt; 0">
                                <xsl:value-of select="$id-val"/>
                                <xsl:value-of select="generate-id()"/>

The problem with the above, and why I never use it, is the very small (but not zero) chance that your document author creates XML along the lines of the following thinking it is not going to be used by other authors:


... and then the processor you use coincidentally returns that very same string as a generated identifier for a different node. It is a remote chance, but you cannot guarantee there won't be a value collision.

I tell my students that if they use generate-id() for a value set they should *only* use generate-id() for all values in the set.

However, I also use some of the IDs for cross-referencing for PDF output and
HTML. So generating the id dynamicly is something I can't always do, unless
I am missing the obvious?

Perhaps you are missing something ... XSLT was originally designed for use with XSL-FO ... the specification for generate-id() requires the return value to be a valid XML name, suitable for cross-referencing *within* PDF files and HTML files. Yours is the use case for which generate-id() was created: ensuring uniqueness amongst multiple aggregated source trees for the purposes of cross-referencing using XML/HTML-suitable identifier values.

What you lose is the ability to link from outside *in* to your aggregated file, in which case your uniqueness guarantee is obliged to be pushed back to the authoring side. If you are linking from outside in and two authors have used the same value, you have no idea which one is the intended one. And then there is a whole maintenance question of tracking who is using which identifiers and what they mean. In which case Michael's code can be used as a check.

I hope this helps.

. . . . . . . . . . . . Ken

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