Re: Cheaper to prepend or append an item to a sequence

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Subject: Re: Cheaper to prepend or append an item to a sequence?
From: Abel Braaksma <abel.online@xxxxxxxxx>
Date: Tue, 22 Feb 2011 20:44:44 +0100

PQQP5QP;P0P2,

Actually, it _is_ dependent on the current node. //@id gets all @id nodes in the document. The next "[..]" means "filter these nodes by the following expression". That expression is a node-test: "not(ancestor::meta)", which is applied to the _current_ node (the current @id-node).

That doesn't mean that a processor cannot optimize that, but in this case that might proof futile: no single element can contain multiple attributes with the same name. Hence the processor will have to test the predicate for each and every found id-attribute.

In short: no, it cannot be calculated only once.

Kind regards,
Abel Braaksm

On 22-2-2011 20:26, PQQP5QP;P0P2 P!P5P4P>P2 wrote:

@id = //@id except (@id, //meta//@id) - yep... good idea

but i think that even //@id[not(ancestor::meta)] should be calculated
only once since it not depend from current node - is not it? is
optimizer capable to recognize context dependant from context
independant XPath fragments inside predicate and calculate independant
fragments only once instead calculating it every time for each node?

Current Thread

Re: Cheaper to prepend or append an item to a sequence?, (continued)
- Dimitre Novatchev - 22 Feb 2011 13:59:29 -0000
  - Michael Kay - 22 Feb 2011 14:32:43 -0000
    - Dimitre Novatchev - 22 Feb 2011 14:41:14 -0000
    - Вячеслав Седов - 22 Feb 2011 19:26:47 -0000
    - Abel Braaksma - 22 Feb 2011 19:45:01 -0000 <=
    - Вячеслав Седов - 22 Feb 2011 19:51:51 -0000
    - Abel Braaksma - 22 Feb 2011 20:02:31 -0000
    - Вячеслав Седов - 22 Feb 2011 20:07:01 -0000
    - iwanttokeepanon - 22 Feb 2011 20:00:59 -0000

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