Subject: Re: [xsl] XSLT/XPath 2.0 (was "Identifying two tags...") From: Jeni Tennison <jeni@xxxxxxxxxxxxxxxx> Date: Thu, 9 May 2002 10:36:06 +0100 |
Hi Wendell, > At 01:59 PM 5/6/2002, Evan Lenz wrote: >>Some people are concerned about the sheer number of functions and >>operators in XPath 2.0 (almost five times as many as in 1.0). A >>related issue is XPath 2.0's heavy dependence on XML Schemas. I >>personally share some of these concerns. The real test of the >>specification's success is the number and quality of >>implementations. Saxon 7 is a good pioneer. It would be great (even >>crucial) to see more efforts sprout up before we approach >>Recommendation status. > > Could you comment more specifically please on the heavy dependence > on Schemas you mention? > > In particular, I'm concerned whether this dependence will mean it's > not possible to use XPath 2, with its sequences, conditionals etc., > in an environment where there is no schema (or no W3C Schema). >From reading the WD, the XPath 2.0 data model specifically supports documents that don't have a schema, and either have a DTD instead or just have a well-formed XML document, or even documents that are partially valid against an XML Schema schema. It could even support other schema languages, although the concept of a named "type" (which isn't really present in, say, RELAX NG) is pretty fundamental to the data model. The mappings from well-formed or DTD-valid documents aren't spelled out in detail yet, but it's likely that they'll be treated exactly as if they had been validated against a fairly loose schema. So a purely well-formed element will be treated like any element with the type xs:anyType (allowing any content and any attributes). Since the "data types" in DTDs (such as NMTOKEN) are supported in XML Schema, they can be used more directly -- the document will look as if it had been validated by an XML Schema generated from the DTD. So you'll be able to use XPath 2.0 without worrying about schema stuff without any problems. With any luck, there will be levels of conformance that mean that processors won't have to support the more complex side of the validation system described in the XPath 2.0 draft, which means that if you're not interested in XML Schema validation then you won't have to be weighed down by a processor that is [ref. http://lists.xml.org/archives/xml-dev/200205/msg00343.html]. Actually, one interesting features of XSLT 2.0 introduced in the latest WD is that you can specify (with xsl:import-schema) what schema is being used *in the stylesheet* rather than waiting to see what a particular source document is using. Currently there's a bit of a confusing situation where the schema you import, which is used for static (compile-time) checking might be completely different from the schema that's used by the source document, with types checked at run time. But if that were remedied, this could lead to being able to have very focused schemas, providing the view of the document that you need for your transformation, rather than relying on the schema that's reported in the instance document. The XSLT 2.0 WD currently only allows you to import XML Schema schemas, but with a bit of pressure perhaps we can persuade them to make an extensible architecture allowing for other types (including DTDs) as well. Cheers, Jeni --- Jeni Tennison http://www.jenitennison.com/ XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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