Re: compute an xpath expression that match a resulted

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Subject: Re: compute an xpath expression that match a resulted node
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 15 Oct 2004 15:14:54 -0400

Majirus,

At 01:26 PM 10/15/2004, you wrote:

Hi all, I have an result fragment named nodeset. using xslt, Is it possible to determine an xpath expression that match this fragment from a source document.

In general, no.

In specific cases, you could get away with

//*[.=$nodeset]

but this depends on every node in your input data having a unique (string) value. (The string value of a node is the concatenation of all its text node descendants.) This is not likely to be the case, though it might be the case for your particular instance of the general question (no two books are likely to have the same author and title, which is what the string value in your example would amount to).

To illustrate the problem, what would you want back if

$nodeset = <author>Michael Kay</author>

and your input data had

<book ISBN= "0-7645-6909-0">
   <title>XSLT programmer's reference 3e </title>
   <author>Michael Kay</author>
</book>
<book ISBN= "0-7645-6909-1">
   <title>XSLT programmer's Guide to British Beers and Ales</title>
   <author>Michael Kay</author>
</book>

what would you want as an XPath expression?

Now, your suggestion of /descendant-or-self::book[@ISBN='0-7645-6909-0'] suggests you want to leverage the fact that you know the values of your ISBN attributes are unique.

That's a good idea, except that Result Tree Fragments in XSLT 1.0 are not transparent, and you have no way to reach in and grab that attribute.

Most of us would recommend using exslt:node-set() or equivalent to make the fragment a node-set -- or to acquire that ISBN another way altogether so you don't have to get it from a result tree. Or use //*[.=$nodeset] and control somehow against getting false hits (say by catching as an exception cases where more than one node comes back).

Good luck,
Wendell

for example:
$nodeset= <book ISBN= "0-7645-6909-0">
                <title>XSLT programmer's reference 3e </title>
                 <author>Michael Kay</author>
             </book>

an xpath expression is: /descendant-orself::book[@ISBN='0-7645-6909-0'].

I have the fragment from a variable ($nodeset).
I used xalan 2.1.4 as xslt processor.

all suggestions are welcome.
I thank all of you in advance.

Majirus

======================================================================
Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
Mulberry Technologies, Inc.                http://www.mulberrytech.com
17 West Jefferson Street                    Direct Phone: 301/315-9635
Suite 207                                          Phone: 301/315-9631
Rockville, MD  20850                                 Fax: 301/315-8285
----------------------------------------------------------------------
  Mulberry Technologies: A Consultancy Specializing in SGML and XML
======================================================================

Current Thread
compute an xpath expression that match a resulted node Majirus FANSI - Fri, 15 Oct 2004 19:21:17 +0200 <Possible follow-ups> Majirus FANSI - Fri, 15 Oct 2004 19:26:54 +0200 Wendell Piez - Fri, 15 Oct 2004 15:14:54 -0400 <=

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