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Re: Venetian Blinds vs Garden of Eden patterns for industry s

  • From: "G. Ken Holman" <gkholman@CraneSoftwrights.com>
  • To: XML-Dev Mailing list <xml-dev@lists.xml.org>
  • Date: Thu, 28 Oct 2010 13:40:14 -0400

Re:  Venetian Blinds vs Garden of Eden patterns for  industry s
At 2010-10-28 18:13 +0100, Pete Cordell wrote:
>Original Message From: "G. Ken Holman"
>>At 2010-10-28 14:32 +0100, Pete Cordell wrote:
>>>Hi David,
>>>It should be ns1:root/a/b/ns2:root/b as Philip says because in the 
>>>scheme I described a and b were unqualified.  As such there's no 
>>>difference in name between b in ns1 and b in ns2 as there would be 
>>>if they were qualified.
>>>I think Philip is right about the issues.  It's down to the 
>>>limitations in XPath expressibility.  You need to say something 
>>>like: b whose qualified parent is in namespace ns1.  Sort 
>>>of   b[qualified-parent-ns()=ns1]!
>>... or if you are matching nodes:
>>  ns1:*/b
>My XPath knowledge is very weak, but does that allow for matching 
>'b' in the 'tree' of:
>ns1:root/a/b  ?

No, you only asked "b whose qualified parent is in namespace ns1"

>I had guessed that ns1:*//b might be better, but I think that 
>expression would match both 'b's in the Philip's 'tree' of:
>Yours confused,

I'm confused what you are looking for.

Given the tree:   ns1:root/a/b/ns2:root/b

ns1:*/b selects nothing
ns1:*//b selects both b's
b[parent::ns1] selects nothing
b[parent::ns2] selects the lowest b only

What *exactly* do you want to address, and from where will you be 
addressing it?  In a select="" using an expression (and if so from 
which context node)?  In a match="" using a pattern (which is a 
subset of XPath expressions)?

I haven't been following the entire thread ... I just bristle when I 
read statements like "It's down to the limitations in XPath 
expressibility" and writing such is like waving a red cape in front 
of me.  I know XPath is *incredibly* expressive and in the classroom 
I try and teach students how to understand the node tree intimately 
in order to compose the most appropriate and least wasteful XPath 
expressions.  The XPath exercise is most often the favourite exercise 
of the entire week in the class.

I've not been following the discussion but that statement of yours 
jumped out at me and quickly got my attention.

I hope this helps.

. . . . . . . . . . Ken

Crane Softwrights Ltd.          http://www.CraneSoftwrights.com/x/
G. Ken Holman                 mailto:gkholman@CraneSoftwrights.com
Male Cancer Awareness Nov'07  http://www.CraneSoftwrights.com/x/bc
Legal business disclaimers:  http://www.CraneSoftwrights.com/legal

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