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Posted to j-users@xalan.apache.org by Sam Prokop <sp...@4tek.de> on 2010/02/12 14:53:39 UTC
Different Current-Node-Set
Hi,
why does Xalan process different current-node-sets, when one node set is sorted?
Example:
XML:
<AAA>
<BBB>
<CCC>A</CCC>
</BBB>
<BBB>
<CCC>B</CCC>
</BBB>
<BBB>
<CCC>A</CCC>
</BBB>
<BBB>
<CCC>C</CCC>
</BBB>
<BBB>
<CCC>B</CCC>
</BBB>
<BBB>
<CCC>B</CCC>
</BBB>
<BBB>
<CCC>A</CCC>
</BBB>
</AAA>
XSL:
<xsl:template match="/">
<xsl:apply-templates select="//AAA/BBB">
<xsl:sort select="CCC"/>
</xsl:apply-templates>
</xsl:template>
<xsl:template match="BBB">
<xsl:value-of select="CCC"/> = <xsl:value-of select="preceding::CCC"/> : <xsl:value-of select="CCC = preceding::CCC"/><br/>
</xsl:template>
Result:
A=:false
A=A:true
A=A:true
B=A:false
B=A:true
B=A:true
C=A:false
Does the comparison "CCC = preceding::CCC" use the sorted Node-Set for preceding and the select "preceding::CCC" use the document node set?
Thanks
Sam
Re: Different Current-Node-Set
Posted by Michael Ludwig <mi...@gmx.de>.
Sam Prokop schrieb am 15.02.2010 um 11:41:21 (+0100):
> I wasn´t aware that compare in Xpath compares to any preceding nodes
> not only the first one.
But of course nothing stops you from going preceding::CCC[1] if that's
what you want - the preceding-axis in in reverse document order, so [1]
will get the closest node to the context node.
--
Michael Ludwig
AW: Different Current-Node-Set
Posted by Sam Prokop <sp...@4tek.de>.
Thanks,
this made things clear. I wasn´t aware that compare in Xpath compares to any preceding nodes not only the first one.
I wanted to archive an Index like:
a | a_c
| a_d
| a_a
b| b_a
| b_d
…
As long as I don´t use substring it worked, if I use substring in the comparison (substring(preceding::CCC,1,2)) it does not work.
Because of, as you described, substring is a string operation and uses only the first node.
So things get a little bit more complicated here.
Cheers
Sam
Hi, Sam.
Sam Prokop <sp...@4tek.de> wrote on 02/12/2010 08:53:39 AM:
> <xsl:template match="/">
> <xsl:apply-templates select="//AAA/BBB">
> <xsl:sort select="CCC"/>
> </xsl:apply-templates>
> </xsl:template>
>
> <xsl:template match="BBB">
> <xsl:value-of select="CCC"/> = <xsl:value-of
> select="preceding::CCC"/> : <xsl:value-of select="CCC = preceding::CCC"/><br/>
> </xsl:template>
>
> Result:
> A=:false
> A=A:true
> A=A:true
> B=A:false
> B=A:true
> B=A:true
> C=A:false
>
> Does the comparison “CCC = preceding::CCC” use the sorted Node-Set
> for preceding and the select “preceding::CCC” use the document node set?
I think this has more to do with the differences in the meaning of the relational operators and of conversion to string than the effect of sorting.
xsl:value-of converts the selected value to string and uses that string value to construct a new text node. That conversion is performed as if the XPath string function was applied to the value.[1] "A node-set is converted to a string by returning the string-value of the node in the node-set that is first in document order. If the node-set is empty, an empty string is returned."
So when you write xsl:value-of select="preceding::CCC" that selects the all the CCC elements that precede the context node (the BBB element) in document order, and the conversion to string selects the first of those. So, except when the context node is the first BBB element which has no preceding CCC elements, the xsl:value-of is always getting the string value of the very first CCC node - that is, "A".
From section 3.4 of XPath 1.0,[2] "If both objects to be compared are node-sets, then the comparison will be true if and only if there is a node in the first node-set and a node in the second node-set such that the result of performing the comparison on the string-values of the two nodes is true."
So when you write, <xsl:value-of select="CCC = preceding::CCC"/>, that selects two sets of nodes: the CCC element children of the BBB element, and all the CCC elements that precede that BBB element in document order. Then, if there is node in the first set and a node in the second set whose string values are equal, the result of the comparison is true. When you come to the first BBB node that has a CCC child with string value "B", for instance, the result of the comparison will be false, but for all subsequent BBB elements with a CCC child with string value "B", the result of the comparison must be true.
I hope that helps to clarify things. If you can describe what you're actually trying to do, somebody might be able to suggest how you could write that in XSLT.
Thanks,
Henry
[1] http://www.w3.org/TR/xpath/#function-string
[2] http://www.w3.org/TR/xpath/#booleans
------------------------------------------------------------------
Henry Zongaro
XML Transformation & Query Development
IBM Canada Lab T/L 313-6044; Phone +1 905 413-6044
mailto:zongaro@ca.ibm.com
Re: Different Current-Node-Set
Posted by Henry Zongaro <zo...@ca.ibm.com>.
Hi, Sam.
Sam Prokop <sp...@4tek.de> wrote on 02/12/2010 08:53:39 AM:
> <xsl:template match="/">
> <xsl:apply-templates select="//AAA/BBB">
> <xsl:sort select="CCC"/>
> </xsl:apply-templates>
> </xsl:template>
>
> <xsl:template match="BBB">
> <xsl:value-of select="CCC"/> = <xsl:value-of
> select="preceding::CCC"/> : <xsl:value-of select="CCC =
preceding::CCC"/><br/>
> </xsl:template>
>
> Result:
> A=:false
> A=A:true
> A=A:true
> B=A:false
> B=A:true
> B=A:true
> C=A:false
>
> Does the comparison “CCC = preceding::CCC” use the sorted Node-Set
> for preceding and the select “preceding::CCC” use the document node
set?
I think this has more to do with the differences in the meaning of the
relational operators and of conversion to string than the effect of
sorting.
xsl:value-of converts the selected value to string and uses that string
value to construct a new text node. That conversion is performed as if
the XPath string function was applied to the value.[1] "A node-set is
converted to a string by returning the string-value of the node in the
node-set that is first in document order. If the node-set is empty, an
empty string is returned."
So when you write xsl:value-of select="preceding::CCC" that selects the
all the CCC elements that precede the context node (the BBB element) in
document order, and the conversion to string selects the first of those.
So, except when the context node is the first BBB element which has no
preceding CCC elements, the xsl:value-of is always getting the string
value of the very first CCC node - that is, "A".
From section 3.4 of XPath 1.0,[2] "If both objects to be compared are
node-sets, then the comparison will be true if and only if there is a node
in the first node-set and a node in the second node-set such that the
result of performing the comparison on the string-values of the two nodes
is true."
So when you write, <xsl:value-of select="CCC = preceding::CCC"/>, that
selects two sets of nodes: the CCC element children of the BBB element,
and all the CCC elements that precede that BBB element in document order.
Then, if there is node in the first set and a node in the second set whose
string values are equal, the result of the comparison is true. When you
come to the first BBB node that has a CCC child with string value "B", for
instance, the result of the comparison will be false, but for all
subsequent BBB elements with a CCC child with string value "B", the result
of the comparison must be true.
I hope that helps to clarify things. If you can describe what you're
actually trying to do, somebody might be able to suggest how you could
write that in XSLT.
Thanks,
Henry
[1] http://www.w3.org/TR/xpath/#function-string
[2] http://www.w3.org/TR/xpath/#booleans
------------------------------------------------------------------
Henry Zongaro
XML Transformation & Query Development
IBM Canada Lab T/L 313-6044; Phone +1 905 413-6044
mailto:zongaro@ca.ibm.com