Re: [xsl] FW: Stopping recursion

Subject: Re: [xsl] FW: Stopping recursion
From: "Mark Seaborne" <mseaborne@xxxxxxxxxxxxxxxxx>
Date: Tue, 22 Nov 2005 11:33:00 +0000
> From: Michael Kay <mike@xxxxxxxxxxxx>
> Reply-To: <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
> Date: Tue, 22 Nov 2005 11:21:07 -0000
> To: <xsl-list@xxxxxxxxxxxxxxxxxxxxxx>
> Subject: RE: [xsl] FW: Stopping recursion
>
> There are a few problems with this stylesheet - for example I don't think
it
> handles a no-namespace schema, or model groups, or types derived by
> extension, or perhaps quite a few other things. I'm also not sure whether
> the test test=".//@namespace='http://www.w3.org/1999/xlink'" is doing the
> right thing: this seems designed to catch element and attribute wildcards,
> but I would have thought you also wanted to catch XLink attributes declared
> explicitly.

True, though to be fair the stylesheet only has to work with the subset of
WXS that I know we are using, so I have taken shortcuts.

> However, to stick to the question you are asking: I think you need to
> separate the functionality into two parts: a template that determines
> whether an element directly-or-indirectly allows XLink attributes, and a
> template that adds an xml:base attribute. The logic should be "if this
> element declaration directly-or-indirectly allows XLink attributes, then
add
> an xml:base attribute", where the logic for testing each element
declaration
> returns a yes/no result but does not produce a modified element declaration
> as output.
>
> This logic will visit the same element many times, which of course has
> performance implications. An easy but non-standard answer to that is Saxon
> memo functions. A more portable answer is to pass parameters on your
> recursive calls indicating the elements already visited: perhaps two lists,
> one for those known to allow XLink attributes, another for those known not
> to.

Thanks very much, most useful.

All the best

Mark

> Michael Kay
> http://www.saxonica.com/
>
>
>> -----Original Message-----
>> From: Mark Seaborne [mailto:mseaborne@xxxxxxxxxxxxxxxxx]
>> Sent: 22 November 2005 11:00
>> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
>> Subject: [xsl] FW: Stopping recursion
>>
>> Hi,
>>
>> I have a 1.0 stylesheet that takes a WXS schema and adds
>> xml:base to certain
>> complex type definitions. The rule for inclusion of the
>> attribute is that
>> the complex type must either include directly, or have a descendent in
>> another complex type that includes the XLink namespace.
>>
>> So the stylesheet recurses through each complex type and
>> tests to see if
>> they contain anything belonging to the XLink namespace. If the type is
>> itself a complex type the template is called again to check
>> to see if that
>> one has any elements within the XLink namespace, and so on.
>> If the XLink
>> namespace is found then <xsd:attribute ref="xml:base"/> is output.
>>
>> My problem is that once the XLink namespace is found I would like the
>> recursion to stop, mainly because if the namespace is found
>> in more than one
>> descendent element/attribute declaration the attribute is
>> added multiple
>> times.
>>
>> I suspect that either my approach is totally wrong, or this
>> is a common
>> enough problem that there is a design pattern I can use to achieve the
>> effect I want, but I haven't hit on the key words to find it. So any
>> pointers would be gratefully received.
>>
>> This is the template causing the problem:
>>
>> <xsl:template match="xsd:element" mode="findXLink">
>>    <xsl:choose>
>>    <!-- if the element is declared locally (has a type attribute_ -->
>>       <xsl:when test="@type">
>>         <!-- remove the namespace prefix from the qname -->
>>         <xsl:variable name="myType"
>> select="substring-after(@type, ':')"/>
>>         <xsl:for-each
>> select="/xsd:schema/xsd:complexType[@name = $myType]">
>>         <xsl:choose>
>>         <!-- if the complex type definition includes anything
>> in the XLink
>> namespace output the xml:base attribute -->
>>           <xsl:when
>> test=".//@namespace='http://www.w3.org/1999/xlink'">
>>             <xsd:attribute ref="xml:base"/>
>>           </xsl:when>
>>        <!-- otherwise apply this template to all of the
>> elements declared
>> within the complex type -->
>>           <xsl:otherwise>
>>              <xsl:apply-templates select=".//xsd:element"
>> mode="findXLink"/>
>>           </xsl:otherwise>
>>         </xsl:choose>
>>       </xsl:for-each>
>>     </xsl:when>
>>     <!-- otherwise assume that the element references a
>> globally declared
>> element, so look for that -->
>>     <xsl:otherwise>
>>       <xsl:variable name="myName"
>> select="substring-after(@ref, ':')"/>
>>       <xsl:apply-templates select="//xsd:element[@name = $myName]"
>> mode="findXLink"/>
>>      </xsl:otherwise>
>>    </xsl:choose>
>> </xsl:template>
>>
>> All the best
>>
>> Mark
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>
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