RE: [xsl] XSL: For-Each Efficient or Not?

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Subject: RE: XSL: For-Each Efficient or Not?
From: Johannes Döbler <jd@xxxxxxxxxxxxxx>
Date: Mon, 01 Jul 2002 18:59:47 +0200

taking "child::*[position()=1 and name()='factorof']" as example:

A straightforward implementation will evaluate the child axis expression to a node-set and then apply the predicate to each node in the set. A clever implementation would use the predicate to terminate the child axis evaluation after the first inspected node (because of position() = 1). Not only the evaluation sequence changes but also the character of the expressions (a filter expression is turned into a loop termination criterion)

The serious implementation problem is to recognize optimization possibilities _and_ how to implement the optimization in a general way without destroying the clean implementation of the straightforward processing model.

Possible solution: Internally recognize special expressions during parse time and transform it to another expression which is processed by the straightforward processing model:

"child::*[position()=1 and name()='factorof']"
will be transformed to
"firstchild::*[name()='factorof']"
which could easily be reduced to
"firstchild::factorof'"

with the use of a processor internal pseudo-axis "firstchild".

Johannes

Wendell wrote:
>m:apply[factorof[not(preceding-sibling::*)]]

>will be better than

>m:apply[child::*[position()=1 and name()='factorof']]

at first I didn't get your point on this one. I supposed on further
consideration that it was right, although it seems like it would be
mainly dependent on the order in which xpath is evaluated by the
processor, I mean that a reasonably clever processor would evaluate
[position()=1 and name()='factorof'] first and then from there look for
any child::* which matched this, with the result that it would only
check the first child to see if it had a name of factorof?
Am I very wrong in this supposition?

XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list

Current Thread

RE: XSL: For-Each Efficient or Not?, (continued)
- Michael Kay - Mon, 1 Jul 2002 10:30:37 -0400 (EDT)
  - Kevin Jones - Mon, 1 Jul 2002 11:10:55 -0400 (EDT)
    - Wendell Piez - Mon, 1 Jul 2002 11:47:52 -0400 (EDT)
    - bryan - Mon, 1 Jul 2002 12:08:49 -0400 (EDT)
    - Johannes Döbler - Mon, 1 Jul 2002 12:57:29 -0400 (EDT) <=
    - Wendell Piez - Mon, 1 Jul 2002 13:57:16 -0400 (EDT)
    - Michael Kay - Mon, 1 Jul 2002 15:09:03 -0400 (EDT)
    - Wendell Piez - Mon, 1 Jul 2002 17:49:48 -0400 (EDT)
    - Michael Kay - Tue, 2 Jul 2002 04:11:16 -0400 (EDT)

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