Fwd: Pattern matching error in xsl:key

---------- Forwarded message ---------
From: Ihe Onwuka <[email protected]>
Date: Sat, Sep 5, 2020 at 2:08 PM
Subject: Re: [saxon] Pattern matching error in xsl:key
To: Dimitre Novatchev <[email protected]>



On Sat, Sep 5, 2020 at 1:54 PM Dimitre Novatchev <[email protected]>
wrote:

> > So I have ended up doing an eq comparison and quoting the $source and
> $target, which is what I was trying to avoid.
>
> Why do you think any logical reasoning would result in deciding that the
> type of $source below must be a string?
>
> >  <xsl:param name="source" select="4.0"/>
>
> The value of the "select" attribute is evaluated as an XPath expression,
> What is the type of the xpath expression (hint: it is obviously a decimal
> number):
>
>    4.0
>
> Why do you think anyone should conclude that this is a string?
>
> Just curious...
>
> Cheers,
> Dimitre
>
>
Of course there is no logical reason for anyone to conclude that 4.0 is a
string.
Of course it's obviously a decimal number.

So now let's apply that logic to the other half of the problem.

What is the logical reason ( not the reason the spec gives,  the logical
reason) for concluding that in the @from attribute below 4.0 is a string

<changes from="4.0" to="4.1">
     <rename>
        <metadata/>
     </rename>
  </changes>

Isn't it obviously a decimal number?


On Sat, Sep 5, 2020 at 10:49 AM Ihe Onwuka <[email protected]> wrote:
>
>>
>>
>> On Sat, Sep 5, 2020 at 11:56 AM Martin Honnen <[email protected]>
>> wrote:
>>
>>> 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".
>>>
>>>
>> Correction to my earlier post.
>> Using = instead of eq changes the behaviour of the program and it ends up
>> incorrectly omitting some of the output.
>>
>> I'm not going to investigate why because I shouldn't be using an
>> existential evaluator anyway.
>>
>> So I have ended up doing an eq comparison and quoting the $source and
>> $target, which is what I was trying to avoid.
>>
>>
>>
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>> [email protected]
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>
>
>
> --
> Cheers,
> Dimitre Novatchev
> ---------------------------------------
> Truly great madness cannot be achieved without significant intelligence.
> ---------------------------------------
> To invent, you need a good imagination and a pile of junk
> -------------------------------------
> Never fight an inanimate object
> -------------------------------------
> To avoid situations in which you might make mistakes may be the
> biggest mistake of all
> ------------------------------------
> Quality means doing it right when no one is looking.
> -------------------------------------
> You've achieved success in your field when you don't know whether what
> you're doing is work or play
> -------------------------------------
> To achieve the impossible dream, try going to sleep.
> -------------------------------------
> Facts do not cease to exist because they are ignored.
> -------------------------------------
> Typing monkeys will write all Shakespeare's works in 200yrs.Will they
> write all patents, too? :)
> -------------------------------------
> Sanity is madness put to good use.
> -------------------------------------
> I finally figured out the only reason to be alive is to enjoy it.
>
>

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