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Re: Action Item: rework 4.1.4 (cf. http://www.w3.org/2007/05/30-i18nits-minutes.html#action06)

From: Jirka Kosek <jirka@kosek.cz>
Date: Thu, 14 Jun 2007 14:28:54 +0200
Message-ID: <46713486.4090202@kosek.cz>
To: Felix Sasaki <fsasaki@w3.org>
CC: "Lieske, Christian" <christian.lieske@sap.com>, public-i18n-its@w3.org
Felix Sasaki wrote:

> The best free tutorial I know is available at ZVON
> http://www.zvon.org/xxl/XPathTutorial/General/examples.html .
> 
> The difference between two XPath expressions at the end of your proposal
> is that //del/descendant-or-self::*/@* has 3 steps
> //del
> //descendant-or-self::*
> /@*
> 
> whereas //@*[ancestor::del] has only one step and a predicate
> //@*
> [ancestor::del]
> 
> which is less effort to compute. Maybe we should add such an explanation
> to the example (without the detailed steps).

I would prefer not adding such explanation into example. The problem is
that it is very hard to compare efficiency of two XPath expression as it
depends on particular XPath implementation used. Clever optimizer can
automatically rewrite former expression into later. Moreover in some
expressions efficiency could depend on frequency of particular elements
and attributes that are evaluated in XPath expression.

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Received on Thursday, 14 June 2007 12:28:43 GMT

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