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Question about result tree fragments vs. node sets in parameters
- To: xsl-list at mulberrytech dot com
- Subject: Question about result tree fragments vs. node sets in parameters
- From: jim hopp <jhopp at pacbell dot net>
- Date: Sat, 26 Aug 2000 14:33:05 -0700
- Reply-To: xsl-list at mulberrytech dot com
I'm confused about when a parameter contains a result tree fragment and
when it contains a node set. I get similar results (an error) in both
Xalan and InstantSaxon, so I suspect the difficulty is caused by my
confusion rather than a bug in the XSLT processors. (I'm running Xalan
1.2D01 with Sun's JDK 1.3 and Client Hotspot, and InstantSaxon 5.4.1.)
As far as I can tell, the error appears to arise on the expression
"$step_data/@Instance" where step_data is a parameter passed to the
template AND the template has been invoked with an <xsl:apply-templates
select="document('tree_error1.xml')"><xsl:with-param name="step_data"
select="$step_data"/></xsl:apply-templates>. step_data is a variable
that, I believe, contains a node set: <xsl:variable name="step_data"
value="."/>. If I invoke "$step_data/@Instance" in the invoking
template (before the apply-templates call), the expression returns what
I expected, which is why I believe that the variable is indeed a node set.
My understanding of variables and parameters (from reading the XSLT spec
and Mike Kay's excellent book) is that the data type of a variable or
parameter will always be a node-set if the value of the variable/parm
was set with a SELECT expression, and the data type would be a result
tree fragment only if the value were set with a non-empty template
body. Is this correct? If it is, I would expect the parameter
step_data to be a node-set, not a result tree fragment.
Here's the XSL stylesheet:
<?xml version="1.0" standalone="yes"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html"/>
<xsl:template match="suspended_step">
<xsl:variable name="step_data" select="."/>
<HTML>
<HEAD>
<TITLE><xsl:value-of select="@Instance"/></TITLE>
</HEAD>
<BODY>
<H1>Value of $step_data/@Instance is /<xsl:value-of
select="$step_data/@Instance"/>/</H1>
<H1>Count of step_data before template invocation
is <xsl:value-of select="count($step_data)"/></H1>
(Invoking template)
<xsl:apply-templates select="document('tree_error2.xml')">
<xsl:with-param name="step_data" select="$step_data"/>
</xsl:apply-templates>
(Returned from template)
</BODY>
</HTML>
</xsl:template>
<xsl:template match="top_element">
<xsl:param name="step_data"/>
<H1>Value of $step_data/@Instance is /<xsl:value-of
select="$step_data/@Instance"/>/</H1>
<H1>Value of string($step_data) is /<xsl:value-of
select="string($step_data)"/>/</H1>
<H1>Count of $step_data is <xsl:value-of select="count($step_data)"/></H1>
</xsl:template>
</xsl:stylesheet>
Here's the XML that the stylesheet is processing:
<?xml version="1.0" encoding="iso-8859-1" standalone="yes" ?>
<suspended_step Instance="3088.3876">
<Instance>
<RI DID="hello" IID="1461.5152" />
</Instance>
</suspended_step>
Here's the contents of tree_error2.xml:
<?xml version="1.0" encoding="iso-8859-1" standalone="yes" ?>
<top_element Instance="3088.3876">
<Instance>
<RI DID="hello" IID="1461.5152" />
</Instance>
</top_element>
Here's the InstantSaxon output:
C:\DVLP\docs>\saxon\saxon tree_error.xml tree_error.xsl
<HTML>
<HEAD>
<TITLE>3088.3876</TITLE>
</HEAD>
<BODY>
<H1>Value of $step_data/@Instance is /3088.3876/</H1>
<H1>Count of step_data before template invocation
is 1
</H1>
(Invoking template)
<H1>Value of $step_data/@Instance is /At xsl:value-of on line 26 of file:/
C:/DVLP/docs/tree_error.xsl: Cannot convert value [""] to a node-set
Here's the Xalan output (run with -TT -TS -TG -V):
>>>>>>> Xalan Version 1.2D01, XML4J Version Xerces 1.1.2<<<<<<<
========= Parsing file:C:/DVLP/docs/tree_error.xsl ==========
Parse of file:C:/DVLP/docs/tree_error.xsl took 820 milliseconds
========= Parsing file:C:/DVLP/docs/tree_error.xml ==========
Parse of file:C:/DVLP/docs/tree_error.xml took 280 milliseconds
=============================
Transforming...
STARTDOCUMENT
Line #0, Column #0: xsl:template match='/'
Line #5, Column #40: xsl:template match='suspended_step'
Line #6, Column #48: xsl:variable, select='.':
org.apache.xalan.xpath.dtm.DTMProxy@6b7859
STARTDOCUMENT
STARTELEMENT: HTML
STARTELEMENT: HEAD
Line #9, Column #49: xsl:value-of, select='@Instance':
org.apache.xalan.xpath.dtm.DTMProxy@30e280
STARTELEMENT: TITLE
CHARACTERS: 3088.3876
ENDELEMENT: TITLE
ENDELEMENT: HEAD
STARTELEMENT: BODY
STARTELEMENT: H1
CHARACTERS: Value of $step_data/@Instance is /
Line #12, Column #92: xsl:value-of, select='$step_data/@Instance':
org.apache.xalan.xpath.dtm.DTMProxy@4cb029
CHARACTERS: 3088.3876
CHARACTERS: /
ENDELEMENT: H1
STARTELEMENT: H1
CHARACTERS: Count of step_data before template invocation
is
Line #14, Column #56: xsl:value-of, select='count($step_data)': 1
CHARACTERS: 1
ENDELEMENT: H1
CHARACTERS:
(Invoking template)
Line #16, Column #64: xsl:apply-templates,
select='document('tree_error2.xml')':
org.apache.xalan.xpath.dtm.DTMProxy@7bd9f2
Line #0, Column #0: xsl:template match='/'
Line #24, Column #37: xsl:template match='top_element'
STARTELEMENT: H1
CHARACTERS: Value of $step_data/@Instance is /
XPATH: Can not convert #RTREEFRAG to a NodeList!
Xalan: was not successful.
XSLProcessor: done
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