Re: [xml-dev] Concerned about the increasing reliance on XPath

[Michael Kay <mike@saxonica.com>]

On 07/05/2011 14:51, Costello, Roger L. wrote:
> Hi Folks,
>
> XPath is a fabulous language. It is incredibly powerful. It is a large, rich language.
>
> I have observed in increasing usage of XPath.
>
> For example, in XML Schema 1.1 the new assert element uses XPath to express constraints:
>
>      <assert test="XPath" />
>
> XPath gives a lot of power to the assert element.
>
> But it also means that a lot of power is needed to evaluate the assert element.
>
> To evaluate that tiny, innocuous assert element you need to implement the entire XPath language.
>

I'm much more concerned about the proliferation of different dialects 
and varieties of XPath. I strongly encouraged the XML Schema WG to 
support the whole of XPath 2.0 in assertions for two reasons:

(a) it's very difficult for users if XSD, XForms, XProc, XSLT, etc all 
use different XPath subsets

(b) it means that XSD implementors can use an off-the-shelf XPath engine 
rather than implementing their own. (Both existing XSD 1.1 processors - 
Xerces and Saxon - use XPath libraries that were originally written for 
a different purpose).

Michael Kay
Saxonica