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Re: Re: XPath to select node according to xml:lang at

Subject: Re: Re: XPath to select node according to xml:lang attribute
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Fri, 15 Apr 2011 18:37:06 -0400
Re:  Re: XPath to select node according to xml:lang  at
Hi,

On 4/15/2011 2:22 PM, Chris wrote:
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On 04/15/2011 02:18 PM, Philipp Kursawe wrote:
Hmm I cannot use XSLT in my context. I can only use XPath. So I guess
I would have to select "en-us" first and see if there is a result, if
not select "en" and so on. Or could I "||" chain multiple XPath
selects?
//text[@id='color' and lang('en-us')] || //text[@id='color' and
lang('en')] || //text[@id='color']

Not sure what your context is... You canbt put the || in an XPath, but if youbre in some procedural language like Perl or Java, then yes. Pseudocode:

color_label = select( "//text[@id='color' and lang('en-us')]" ) ||
               select( "//text[@id='color' and lang('en')]" ) ||
               select( "//text[@id='color']" )

That would (presuming normal behavior of logical or) get the best match
for you.

Keep in mind, however, that what we have in XPath 1.0 "|" is a union operation, not an "or". So,


//text[@id='color' and lang('en-us')] |
//text[@id='color' and lang('en')] |
//text[@id='color']

will get us all the nodes in //text that have @id='color', irrespective of their lang() value, because the third term in the union collects them.

To do a cascading conditional like this in XPath 1.0 alone generally requires building conditionals into the predicates, as in

//text[@id='color'][
  @xml:lang='en-us' or
  (@xml:lang='en' and not(../@xml:lang='en-us') or
  not(../@xml:lang='en-us' or../@xml:lang='en')] ]

where the fallback cases (the second and third operands of the boolean 'or' here) are excluded by filtering themselves out when the preferred cases are available.

Here the attribute values are tested directly since the lang() function works only on the context node, and we have to test the siblings. (So we have to do without the case-insensitive test built into lang().)

This is easier in XPath 2.0, where we can do something like

//text[@id='color]/(.[lang('en-us')],.[lang('en')],.)[1]

Cheers,
Wendell

======================================================================
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
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  Mulberry Technologies: A Consultancy Specializing in SGML and XML
======================================================================

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