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

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

At 10:20 PM 7/21/2006, Mike wrote:
> I've never heard of xsl:key but the second illustration here:
>
>  http://www.cranesoftwrights.com/resources/xslkeys/index.htm
>
> 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.

Cheers,
Wendell