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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XPath 2.0 Best Practice Issue: Graceful Degradation
 > 1. Avoid relative XPath expressions. both of your expressions started with / so were not relative. but comparing > (a) //altitude * .3048 > (b) /FAA/airplane[@tailnum='C3H1']/altitude[@unit='feet'] * .3048 sometimes you want to ties an expression to a rigid input structure (b) and sometimes you want to be fleaxible in the face of varying input, (a) or more commonly something like <xsl:template match="altituse" Its impossible to give a general rule that one way is good and the other bad. > 2. Whenever possible, stick with XPath 1.0 expressions; they can be > processed by XPath 1.0 and XPath 2.0 processors. There are contexts (eg client side browser use) where sticking with xpath 1 for nw makes sense, but if you've yused xpath2 for a while sticking with xpath 1 is fairly painful, it's not realistic to expect people to make code work on both systems. If you need to run on an xpath 1 processor, use xpath 1, if you don't commit to xpath 2 and use its features as appropriate. > 3. Keep XPath statements focused on processing, rather than > 3. validation. unless you are just using path to express validation constraints eg schematron. > 1. I now question the value of schema-element(). Should this function > ever be used? Perhaps it should be avoided? Yes of course, in many situations you know what that you are going to schema validate the input and you know you have a schema processor. Sayiing that you should only write xpaths that can be run anywhere without any knowledge of the context is making massive assumptios about the usage. However there are situations where you want expressions to run in a wide range of contexts and "degrade gracefully" in the terminology of the thread, and in that situation (only) it makes sense to avoid cconstructs that will make static compile time errors on some systems. > 2. Do you agree with all the above? Not really:-) David ________________________________________________________________________ The Numerical Algorithms Group Ltd is a company registered in England and Wales with company number 1249803. The registered office is: Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom. This e-mail has been scanned for all viruses by Star. The service is powered by MessageLabs. ________________________________________________________________________ 
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