Re: [xml-dev] Using Schematron to express a rule for a QName value?

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

At 2012-09-21 15:40 +0000, Costello, Roger L. wrote:
>Hi Folks,
>
>Consider the following XML document. There is an <Item> element 
>which has a "name" attribute:
>
><Test xmlns:wid="http://www.widget.org";>
>     <Item name="wid:widget" />
></Test>
>
>The value of  @name is a QName.
>
>I want a Schematron rule that expresses this:
>
>       The <Item> element must have a
>       name attribute whose value is "widget"
>       in the http://www.widget.org namespace.
>       (The value of @name is a QName)
>
>So I created this Schematron document:
>
><sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron";
>                         xmlns:xsd="http://www.w3.org/2001/XMLSchema";
>                         xmlns:w="http://www.widget.org";
>                        queryBinding="xslt2">
>
>    <sch:pattern id="QName-Test">
>
>       <sch:rule context="Item">
>
>          <sch:assert test="resolve-QName(@name, .)  eq 
> xsd:QName('w:widget')">
>                The value of the name attribute must
>                be 'widget' in the http://www.widget.org
>                namespace.
>          </sch:assert>
>
>       </sch:rule>
>
>    </sch:pattern>
>
></sch:schema>
>
>When I validated the XML document against the Schematron schema I 
>got this error:
>
>       Namespace prefix {w} has not been declared
>
>Any ideas on what the problem is?

You are missing a Schematron namespace declaration:

   <sch:ns prefix="w" uri="http://www.widget.org"/>

While it may appear you have satisfied the binding in the Schematron 
schema expression, when this gets translated to XSLT there is nothing 
in the Schematron specification that migrates in-scope namespace 
declarations automatically to the runtime artefact that does the 
actual validation.  Thus, by the time the XSLT of the compiled schema 
is running, the XPath expression with the prefix does not have a 
binding in scope.

The explicit Schematron namespace declaration is meant to address that.

I hope this helps.

. . . . . . . . Ken

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