Re: [xsl] Does the count() function require access to the whole subtree?

[Dimitre Novatchev <dnovatchev@xxxxxxxxx>]

On Sun, Jan 12, 2014 at 5:27 AM, David Carlisle <davidc@xxxxxxxxx> wrote:
> I think the way to think of it is to see that given a sequence of nodes
> $seq then count($seq) doesn't require you to access anything that you
> haven't already accessed (even if you are in a streaming context and
> some of the nodes are still being streamed)

If the context node has N children nodes, it isn't possible to know
that there are K children, unless at least these K children nodes (and
their sub-trees) are already read (confirmed to exist).

So, to test the existence of

   node()[$K]

one will need to confirm this by reading through at least K children nodes.

Even worse, to test the existence of:

  mySpecificNamedChild[1]

one may need to read *all* the children of the context node.


These observations show, that  in general "count()" , using the chosen
terminology, is clearly an "absorption" operation and not an
"inspection" operation, though there is one exception when count() is
applied on nodes, whose number is statically known -- such as:

   count(/)

   count(..)

   count(.)

Of course, it is meaningless to use the above three expressions,
because we already know what they would exactly produce ...



-- 
Cheers,
Dimitre Novatchev
---------------------------------------
Truly great madness cannot be achieved without significant intelligence.
---------------------------------------
To invent, you need a good imagination and a pile of junk
-------------------------------------
Never fight an inanimate object
-------------------------------------
To avoid situations in which you might make mistakes may be the
biggest mistake of all
------------------------------------
Quality means doing it right when no one is looking.
-------------------------------------
You've achieved success in your field when you don't know whether what
you're doing is work or play
-------------------------------------
To achieve the impossible dream, try going to sleep.
-------------------------------------
Facts do not cease to exist because they are ignored.
-------------------------------------
Typing monkeys will write all Shakespeare's works in 200yrs.Will they
write all patents, too? :)
-------------------------------------
I finally figured out the only reason to be alive is to enjoy it.