Re: XPath 2.0: Collection-Valued Expressions (Was: Re:
Hi Mike, >> Oh, OK, I didn't realise. Guess it's our fault for letting the >> multiple requests for dynamic evaluation and its inclusion in >> several XSLT processors speak for themselves rather than making a >> formal noise about the requirement. Can I request now that it's on >> the requirements list for XPath 3.0 (assuming we get that far)? > > You can request that it's added to the requirements for 2.0 if you > want (by commenting on the published 2.0 requirements). Whether your > request will succeed, I cannot say... OK, worth a shot. Mike, please could you forward this to mailto:xsl-editors@xxxxxx as messages that I send to W3C mailing lists do not get through. As XSLT use becomes more sophisticated, there are a growing number of situations where users wish to use XPaths within the source XML for a transformation, or passed in as parameters, and have these XPaths evaluated by the XSLT processor. Typical use cases are: * XML specifications of table columns holding an XPath pointing to the values to be held in each column * support for user-defined sorts * search queries where the searcher specifies the search field as an XPath * simplified XPointers in XInclude or XLink elements One well articulated example is described at: http://aspn.activestate.com/ASPN/Mail/Message/679116 This functionality is supported by extension functions such as saxon:evaluate() and xalan:evaluate(). However, as with other common extension functions, these are processor-specific. Also, the complexity involved (in particular access to the context in which the XPath is evaluated, and therefore things like the context node, function library, variable assignments and namespace mappings) means that user-defined functions to achieve this functionality would be substantially inferior to those that were built-in to the processor. The functionality could possibly be achieved through: * an expression data type in a manner similar to saxon:expression(), which would also lend itself to satisfying XPath requirement 2.5 "Should Support Aggregation Functions Over Collection-Valued Expressions" * an evaluate() function similar to saxon:evaluate() and xalan:evaluate() * using attribute value templates within XSLT attributes (perhaps described in terms of simplifying the process of generating XSLT from XSLT and using the result as the stylesheet for a transformation) I therefore respectfully request that the WG will reconsider its decision not to include dynamic evaluation in the requirements for XPath/XSLT 2.0. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/ XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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