Hi Neal,
I find it easy to think of XSL as an "XML Programming Language" of sorts.
That is, it has sequence, selection, and iteration, just as any prgramming
technology does. A Template is similar to a function, with the exception
that along with simply calling it, you can automate the calling of it, by
using <xsl:apply-templates /> without any arguments, in which the process of
the application of Templates begins at the current node and works downward
recursively from there. A Template name or Select condition is the
"signature" of the Template, and any node which matches the signature of the
Template will execute the Template for that node.
In this case, you have a top-level "Categories" node, which contains several
nodes with data about a given Category, and several "SubCategories" nodes,
in a similar structure to the "Categories" node.
If I understand you correctly, you want to extend this to include several
"SubSubCategories" nodes under each "SubCategories" node, to indicate a
further level of nesting.
So, let's analyze the first Template:
This Template is called at the top level by <xsl:apply-templates
select="CategoriesList/Categories" />
That indicates that all nodes under the "CategoriesList" node, with node
names matching "Categories" should be processed by the matching Template (or
"function," as it were).
<xsl:template match="Categories">
<LI CLASS="clsHasKids"><xsl:value-of select="CategoryDescr" />
<UL>
<xsl:for-each select="SubCategories">
<LI>
<A TARGET="main">
<xsl:attribute name="HREF">
<xsl:value-of select="URL"/>
</xsl:attribute>
<xsl:value-of select="SubCatDescr" />
</A>
</LI>
</xsl:for-each>
<xsl:if test="Categories"><xsl:apply-templates /></xsl:if>
</UL>
</LI>
</xsl:template>
What this Template does with SubCategories nodes is handles with
<xsl:for-each select="SubCategories">
Each node within that node contains instructions for adding HTML List Items
to the page, for the various nodes under each "SubCategories" node.
At the end of the Template is this instruction: <xsl:if
test="Categories"><xsl:apply-templates /></xsl:if>
This allows Categories to be contained within other Categories. In other
words, it allows for an infinite recursion of Categories within Categories
within Categories, if desired. By testing each node under a given
"Categories" node, and calling "apply-templates" with no parameters, it will
apply any template that has a name of "Categories" to any node under a given
"Categories" node, which, of course, is the current Template. It is like a
recursive function.
Now, it is important to remember that this is a demonstration or example,
and not supposed to represent any real-life situation. After all, it hardly
makes sense for there to be a node called "SubCategories" when any Category
can, in essence, be a sub-category of any other Category. But it does
illustrate several XSL concepts, including several applications of
Templates, and recursion.
I'm a bit confused about this line, though:
<UL><xsl:apply-templates
select="CategoriesList/Categories/SubCategories"/>
It really does nothing, as all the SubCategories are processed under each
"Categories" node. By the time it reaches this line, the entire XML document
has been processed. It has the effect of adding
<UL></UL>
to the page.
Now, again, for the purpose of self-education, I suppose, you want to add
another level below the "SubCategories" level, with a different name
"SubSubCategories." This is where we talk about the various ways to skin an
XSL cat.
One can use loops or Templates in various situations. I suppose the real
question is, which is most efficient for the particular task? The example
uses both, Templates at the top level, and a loop at the bottom level, which
eliminates the need for another Template. I will follow the same example,
and change the inner loop in the Template to another Template call. The
other Template is much like the first, with a loop for "SUBSubCategories" as
this is now the bottom-most node in the tree:
<xsl:template match="/">
<HTML>
<HEAD>
<TITLE>
List <xsl:value-of select="CategoriesList/@TYPE" />
</TITLE>
<LINK REL="stylesheet" TYPE="text/css" HREF="list.css" />
</HEAD>
<BODY>
<H1>
List <xsl:value-of select="CategoriesList/@TYPE" />
</H1>
<UL>
<xsl:apply-templates select="CategoriesList/Categories" />
</UL>
<UL>
<xsl:apply-templates select="CategoriesList/Categories/SubCategories"/>
</UL>
<!--- <P><BUTTON ONCLICK="window.alert(document.body.innerHTML);">View
HTML</BUTTON></P> -->
</BODY>
</HTML>
</xsl:template>
<xsl:template match="Categories">
<LI CLASS="clsHasKids">
<xsl:value-of select="CategoryDescr" />
<xsl:apply-templates select="SubCategories"/>
</LI>
<xsl:if test="Categories">
<xsl:apply-templates />
</xsl:if>
</xsl:template>
<xsl:template match="SubCategories">
<UL>
<LI CLASS="clsHasKids">
<xsl:value-of select="SubCatDescr" />
<xsl:if test="SUBSubCategories">
<UL>
<xsl:for-each select="SUBSubCategories">
<LI>
<A TARGET="main">
<xsl:attribute name="HREF">
<xsl:value-of select="URL"/>
</xsl:attribute>
<xsl:value-of select="SUBSubCatDescr" />
</A>
</LI>
</xsl:for-each>
<xsl:if test="SubCategories">
<xsl:apply-templates />
</xsl:if>
</UL>
</xsl:if>
</LI>
</UL>
</xsl:template>
Let me know if you have any other questions.
--
HTH,
Kevin Spencer
Microsoft MVP
Professional Numbskull
Show me your certification without works,
and I'll show my certification
*by* my works.
