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

[David Carlisle <davidc@xxxxxxxxx>]

On 12/01/2014 11:34, Andrew Welch wrote:
> On 12 January 2014 11:10, Costello, Roger L. <costello@xxxxxxxxx>
> wrote:
> > A couple days ago Michael Kay wrote:
> >
> > Inspection operations on an element are operations that can be
> > performed while positioned at the start tag.
> >
> > Inspection operations include: count(), exists(), name().
> >
> > Absorption operations are operations that require access to the
> > whole subtree.
> >
> > Absorption operations include: string(), data(), xsl:value-of
> >
> > Michael, doesn't the count() function require access to the whole
> > subtree? How would a count be conducted by sitting at the top of a
> > subtree? Perhaps you meant to say that the count() function is an
> > absorption operation?
>
> I wondered this too... I'm guessing you could do a look-ahead of the
>  xml parsing the structure without any text nodes, then you have the
>  'metadata' without the content.  Will be interesting to find out...


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)

conversely string-join($seq,'') or $seq/string(.) do require you to
fully access the content of every node in the sequence so access to
every subtree below each node in the sequence.

David