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Re: XPath filters equivalence

From: David Carlisle <david-news@---------.-----.--.-->
To: NULL
Date: 10/7/2007 12:53:00 AM

Altu wrote:
> Hi,
> 
> Is [p1][p2][p3] the same as [p1 AND p2 and p3] in XPath?

as others have said [][] isn't the same as and if any of the predicates 
use last() or position()
> 
> Also if I have a predicate that starts with "/" or "//", does it
> matter where in the XPath expression it is?
> 
> For example, are these equal:
> 
> /a[/a/b]/c/d
> /a/c[/a/b]/d
> /a/c/d[/a/b]
> 

If a b and c are just element names then the above are all equal and 
equivalent to the xpath2
if(/a/b) then /a/c/d else ()
but if a b c d are standing for arbitrary XPath steps then these may not 
be equivalent as / depends on the current context as it means the 
document node ancestor of the _current node_.
so for example the xpath2
/a[/a/b]/doc('c'xml')/d
the predicate [/a/b] tests in the current docuement
/a/doc('c'xml')[/a/b]/d
here [/a/b] tests in c.xml

David

> or these three:
> 
> /a[//a/b]/c/d
> /a/c/[//a/b]/d
> /a/c/d[//a/b]
> 
> Thanks in advance,
> Al
> 

-- 
http://dpcarlisle.blogspot.com

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