RE: [xsl] Anyone can explain me this syntax?

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Jaime,

At 02:01 PM 1/13/2004, you wrote:
> Thanks Wendell for your complete explanation. While reading your help, I 
> tested another alternative:
>
> ROW[. = key('relacion_x_cobertura', REL_ID)[1]]
>
> and it worked too. The actual XML structure has 35 ROW's, the first 7 
> ROW's has REL_ID = 1, the following 7 ROW's has REL_ID = 2, and so on 
> (this was a particular case where exist 7 ROW's for each REL_ID).
>
> I think that the new way above worked because all of the ROW's are 
> different (besides REL_ID, the ROW has other fields), and since 
> key('relacion_x_cobertura', REL_ID)[1] returns only 1 node where the key 
> is equal to REL_ID, by comparing . with the key value, returns only 1 ROW, 
> the ROW that allows me to group by REL_ID=1, REL_ID=2, until REL_ID = 5.
>
> I think that case is equivalent to generate-id method since all ROW's has 
> at least 1 field different, making the whole ROW different. Is that true?

Yes, if the *value* of each ROW is unique, it can likewise be used to 
deduplicate. Note however this is a big IF, and isn't a reliable assumption 
to make.

To understand this you need to know that $node1 = $node2 is true if the 
(string) value of $node1 is the same as the string value of $node2 -- and 
likewise, $nodeset1 = $nodeset2 is true if the value of *any* of the nodes 
in $nodeset1 is the same as the value of any of the nodes in $nodeset2. 
This is quite a loose and permissive way of construing node-set equality, 
which is actually very useful sometimes. But it means that the "=" equality 
test is not useful for testing node identity unless every node concerned 
has a unique value -- which is rarely the case.

Cheers,
Wendell


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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