Re: Pattern matching error in xsl:key

Am 05.09.2020 um 17:34 schrieb Ihe Onwuka:

> No doubt in excerpting I omitted some relevant info. I'll try and fix
> that. The XML content is in a separate document and globally namespaced.
> Here.
>
> <versionChanges xmlns="http://changes" >
>    <changes from="4.0" to="4.1">
>       <rename>
>          <metadata/>
>       </rename>
>    </changes>
> </versionChanges>
>
> and here is the error message
>
> Warning at char 11 in xsl:key/@match on line 36 column 111 of
> myStylesheet.xsl:
>    XPTY0004  An error occurred matching pattern
>
> {element(Q{http://changes}changes)[((data(attribute::attribute(Q{}from))) eq
>    (atomizeSingleton($source))) and ((data(attribute::attribute(Q{}to))) eq
>    (atomizeSingleton($target)))]}:
>
>     My guess would be that it's a type error connected with the fact
>     you're comparing numbers to strings, but beyond that,
>
>
> I am comparing parameters whose values are 4.0 and 4.1 respectively to
> attributes whose values are 4.0 and 4.1 respectively. Saxon has made
> it's own assumptions about what types they are and come up with that error.

The types are not made up by Saxon but are defined in the XPath/XSLT
specs. In the XSLT code if you declare

   <xsl:param name="source" select="4.0"/>

the expression 4.0 in the select attribute is of type xs:decimal (in a
version="2.0" or version="3.0" XSLT code).

However, in your untyped XML the attribute value of e.g. @from or @to is
of type xs:untypedAtomic.

The eq operator only works if both operands have a comparable type, in
your case the rules in
https://www.w3.org/TR/xpath-31/#id-value-comparisons (5.d) give
"Otherwise, a type error is raised [err:XPTY0004].".

So using = instead of eq is one way to avoid that, as it in 4.a of
https://www.w3.org/TR/xpath-31/#id-general-comparisons stipulates: "If
at least one of the two atomic values is an instance of a numeric type,
then both atomic values are converted to the type xs:double by applying
the fn:number function".







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