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Re: Fwd: xsl:key() and $variables.

Subject: Re: Fwd: xsl:key() and $variables.
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Mon, 24 Jul 2006 11:34:34 -0400
Re:  Fwd: xsl:key() and $variables.
At 10:20 PM 7/21/2006, Mike wrote:
I've never heard of xsl:key but the second illustration here:


looks useful. It seems an xsl:key is like a variable containing
a list of elements that match the xpath expression. But the key()
function allows you to filter on that list further by providing a key
(overloaded term warning). So in the above illustration the xsl:key
statement builds a list of Employee elements and indicates that the SSN
child should be used when a key is supplied to the key() function. So
the key('people',@emp) call says, "fetch all elements in the 'people'
list using the SSN @emp.

Nice writeup.

 Presumably each Employee would have a unique
SSN and therefore the key() call will return one Element.

And if the SSN isn't unique -- or maybe your key value is the surname not the SSN -- you could get several Employees back, all with the same SSN, surname or what have you.

Hence the applicability of keys for de-duplicating and accordingly for grouping.

Note there's nothing you can do with a key that you can't do with brute-force XPath. But since the processor has the information up front to build an index, many expensive tree traversals are avoided and the application scaled much better.


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