XPath and XSL templates

[Tom Alsberg]

Hi there...

I'm recently trying to get a bit acquainted with XML Schemas and XSL.

Now, I have a few questions about XSL stylesheets and templates:

* Is there a way to "enter" a child element of the currently matched
element in the template, so that XPath expressions inside would be
relative to that node? Specifically, I want to do this, in order to
be able to issue xsl:call-template to apply some templates to some
of the child nodes (of course redefining the template many times
with different relative paths is not an option)

* How can I logically AND two expressions in an XPath boolean
expression?

* Can I define more than one template for a match, with one being the
default, but being able to select different ones with
xsl:apply-templates? (I understand that modes are only to select
which elements to process, not which of a few templates to apply to
an element)

* Can you give some suggestions for the following scenario:

What I'm right now working on is defining an XSD type for human names:

<xs:complexType name="personname">
<xs:all minOccurs="1">
<xs:element name="title" type="xs:string" minOccurs="0" />
<xs:element name="given" type="xs:string" />
<xs:element name="middlename" type="xs:string" minOccurs="0" />
<xs:element name="surname" type="xs:string" />
<xs:element name="suffix" type="xs:string" minOccurs="0" />
</xs:all>
</xs:complexType>

What I want, is to have in an XSL stylesheet, a few different
templates for processing a personname, and be able to, in different
contexts (in the same stylesheet), call different templates for it.

E.g., a person:

<name>
<title>Mr.</title>
<given>Richard</given>
<middlename>Lee</middlename>
<surname>Tarpit</surname>
<suffix>the 17th</suffix>
</name>

could be processed as "Richard Tarpit", "Mr. Richard Lee Tarpit",
"Richard Tarpit the 17th", or "Mr. Richard Lee Tarpit the 17th". I
could then define templates for processing the name in those ways,
and in other places within the stylesheet, depending on the context,
call different templates on such a child element.

Thanks, any guidance appreciated,
-- Tom

 

[Martin Honnen]

Now, I have a few questions about XSL stylesheets and templates:

* Is there a way to "enter" a child element of the currently matched
element in the template, so that XPath expressions inside would be
relative to that node? Specifically, I want to do this, in order to
be able to issue xsl:call-template to apply some templates to some
of the child nodes (of course redefining the template many times
with different relative paths is not an option)

I am not sure why you want to enter a child element as you should always
have access to child elements just by using the XPath to it e.g.
./child-element-name

* How can I logically AND two expressions in an XPath boolean
expression?

expression1 and expression2
see http://www.w3.org/TR/xpath#NT-AndExpr

* Can I define more than one template for a match, with one being the
default, but being able to select different ones with
xsl:apply-templates? (I understand that modes are only to select
which elements to process, not which of a few templates to apply to
an element)

I would answer your question with the suggestion to use modes as that is
a way to define more than one template for a match and a way to be able
to select different ones with xsl:apply-templates. However as after the
question you point out that you already know about modes but think they
are not suitable I am not sure what you have in mind.
Maybe you can elaborate.

* Can you give some suggestions for the following scenario:

What I'm right now working on is defining an XSD type for human names:

<xs:complexType name="personname">
<xs:all minOccurs="1">
<xs:element name="title" type="xs:string" minOccurs="0" />
<xs:element name="given" type="xs:string" />
<xs:element name="middlename" type="xs:string" minOccurs="0" />
<xs:element name="surname" type="xs:string" />
<xs:element name="suffix" type="xs:string" minOccurs="0" />
</xs:all>
</xs:complexType>

What I want, is to have in an XSL stylesheet, a few different
templates for processing a personname, and be able to, in different
contexts (in the same stylesheet), call different templates for it.

E.g., a person:

<name>
<title>Mr.</title>
<given>Richard</given>
<middlename>Lee</middlename>
<surname>Tarpit</surname>
<suffix>the 17th</suffix>
</name>

could be processed as "Richard Tarpit", "Mr. Richard Lee Tarpit",
"Richard Tarpit the 17th", or "Mr. Richard Lee Tarpit the 17th". I
could then define templates for processing the name in those ways,
and in other places within the stylesheet, depending on the context,
call different templates on such a child element.

It appears that the example is a follow-up to your previous questions so
lets take that as an example on how to use modes to apply different
templates to the same element: the following stylesheet has two
templates for <name> elements, one with a mode named "short", the other
one with a mode named "full":

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

<xslutput method="html" encoding="UTF-8" />

<xsl:template match="/">
<html>
<head>
<title>Names</title>
</head>
<body>
<div>
<xsl:apply-templates select="name" mode="short" />
</div>
<div>
<xsl:apply-templates select="name" mode="full" />
</div>
</body>
</html>
</xsl:template>

<xsl:template match="name" mode="short">
<xsl:value-of select="concat(given, ' ', surname)" />
</xsl:template>

<xsl:template match="name" mode="full">
<xsl:value-of select="concat(title, ' ', given, ' ', middlename, ' ',
surname, ' ', suffix)" />
</xsl:template>

</xsl:stylesheet>

 

[Patrick TJ McPhee]

% * Is there a way to "enter" a child element of the currently matched
% element in the template, so that XPath expressions inside would be
% relative to that node? Specifically, I want to do this, in order to

You could use a mode specific to that element

<xsl:template match='frankenstein'>
<xsl:apply-templates mode='child-of-frankenstein'/>
<xsl:template>

this will work with call-template as well. You can also use for-each.
The XPath expressions in for-each will be relative to the node
currently being processed.

% * How can I logically AND two expressions in an XPath boolean
% expression?

Using `and'.

% * Can I define more than one template for a match, with one being the
% default, but being able to select different ones with
% xsl:apply-templates? (I understand that modes are only to select
% which elements to process, not which of a few templates to apply to
% an element)

No, modes are to select which of a few templates to apply to an element.
Anyway, there are a few things which might deal with your problem.

You can assign a predicate to a match expression, and use that to
decide which template to apply

<xsl:template match="car[@colour ='blue']">
...
</xsl:template>

<xsl:template match="car[@colour ='red']">
...
</xsl:template>

<xsl:template match="car">
...
</xsl:template>

Roughly speaking, the XSLT processor will choose the most specific
template which matches a node. It's an error to have two equally
specific templates which match the same node, though.

You can set the priority on a match. For instance, if you could have
templates to match cars by the number of doors and a template to match
cars by colour, and say the colour is more important:

<xsl:template match="car[@colour ='blue']" priority='2'>
...
</xsl:template>

<xsl:template match="car[@colour ='red']" priority='2'>
...
</xsl:template>

<xsl:template match='car[@doors = '2'] priority = '1'>
...
</xsl:template>

<xsl:template match='car[@doors = '4'] priority = '1'>
...
</xsl:template>

<xsl:template match="car" priority = '0'>
...
</xsl:template>

This would match the first template for all blue cars, the second template
for all red cars, the third for all cars with 2 doors which are neither
blue nor red, and the fourth for all cars with 4 doors which are neither
blue nor red. The final template would be used for cars which have a
different number of doors or don't have enough information to match
the previous four templates.

% What I'm right now working on is defining an XSD type for human names:

For a tiny subset of humans (says a guy with two middle names .

% What I want, is to have in an XSL stylesheet, a few different
% templates for processing a personname, and be able to, in different
% contexts (in the same stylesheet), call different templates for it.

Sounds you want to use a mode to me. Define a template with a mode
<!-- format a name, current node should be a name element.
also, this should take into account names that run surname givenname
and probably all sorts of other things I can't be bothered with now -->
<xsl:template name='format-name' mode='formal'>
<xsl:value-of select='title'/>
<xsl:text> </xsl:text>
<xsl:value-of select='given'/>
<xsl:text> </xsl:text>
<xsl:value-of select='middle'/>
<xsl:text> </xsl:text>
<xsl:value-of select='surname'/>
</xsl:template>

<xsl:template name='format-name' mode='informal'>
<xsl:value-of select='given'/>
<xsl:text> </xsl:text>
<xsl:value-of select='surname'/>
</xsl:template>

<xsl:template name='format-name' mode='anal'>
<xsl:value-of select='title'/>
<xsl:text> </xsl:text>
<xsl:value-of select='given'/>
<xsl:text> </xsl:text>
<xsl:value-of select='middle'/>
<xsl:text> </xsl:text>
<xsl:value-of select='surname'/>
<xsl:text> </xsl:text>
<xsl:value-of select='suffix'/>
</xsl:template>

Which you would call like this:

<xsl:text>I dined with </xsl:text>
<xsl:call-template name='format-name' mode='anal'>
<xsl:text> last week and I was very interesting.</xsl:text>

 

[Tom Alsberg]

Thank you, you answered some of my questions and misunderstandings.
Please read my comments below, though:

I am not sure why you want to enter a child element as you should always
have access to child elements just by using the XPath to it e.g.
./child-element-name

Quoting myself:
If I have a template that works on a <foo> element, and I'm right now
in a template matching <bar>, and that <bar> element has some <foo>
element inside it, e.g.:

<bar>
<foo>
<xyzzy>
Text
</xyzzy>
</foo>
</bar>

I could want to call the template to handle that <foo> element from
within the template matching the <bar>. Without entering that, I
would have to redefine the <foo> template to access foo/xyzzy instead
of just xyzzy.

Of course that would be easy. But say, if I have some type of
element, which contains xyzzy, but elements of that type can have
different names in different locations, I would have to define the
template for each of those names. Example:

<myfoo>
<xyzzy>
Text 1
</xyzzy>
</myfoo>

<hisfoo>
<xyzzy>
Text 2
</xyzzy>
</hisfoo>

<nofoo>
<xyzzy>
Text 3
</xyzzy>
</nofoo>

myfoo, hisfoo, and nofoo are of the same type (call it foo), and the
same template could handle them (template without a match attribute -
only with a name). However, if I cannot enter them inside the parent
template, I would have to call three different templates from within
it - one that accesses myfoo/xyzzy, another that accesses
hisfoo/xyzzy, and another that accesses nofoo/xyzzy.

expression1 and expression2
see http://www.w3.org/TR/xpath#NT-AndExpr

Thanks. For some reason I missed that.

I would answer your question with the suggestion to use modes as that is
a way to define more than one template for a match and a way to be able
to select different ones with xsl:apply-templates. However as after the
question you point out that you already know about modes but think they
are not suitable I am not sure what you have in mind.
Maybe you can elaborate.

Well, I'm not sure anymore, now with the example you gave it seemed
to work, but I recall I tried something similiar (don't remember
exactly) and it didn't work (the parser told me I have two templates
with the same match).

It appears that the example is a follow-up to your previous questions so
lets take that as an example on how to use modes to apply different
templates to the same element: the following stylesheet has two
templates for <name> elements, one with a mode named "short", the other
one with a mode named "full":
<snip />

Thanks for the example - that seems to be the style of what I need.
I'm not sure why modes didn't work for me at the beginning - I must
have done something wrong.

Thanks again,
-- Tom

 

[Tom Alsberg]

Please read my comments below:

% * Is there a way to "enter" a child element of the currently matched
% element in the template, so that XPath expressions inside would be
% relative to that node? Specifically, I want to do this, in order to

You could use a mode specific to that element

<xsl:template match='frankenstein'>
<xsl:apply-templates mode='child-of-frankenstein'/>
<xsl:template>

But how would this help, though? There could be different children
of frankenstein, with different names (but with the same type/format
of contents), which I would want to process with the same
template... The template shouldn't have to know about what names of
elements it could deal with - when called the context should already
be within that element...

E.g., with my given example of anal human names:

<frankenstein>
<fathername>
<title>Prof.</title>
<given>Cody</given>
<lastname>Frankenstein</lastname>
</fathername>
<mothername>
<title>Mrs.</title>
<given>Lisa</given>
<middlename>Golem</middlename>
<lastname>Hyde</lastname>
<suffix>Junior</suffix>
</motername>
<sistername>
<given>Marjorie</given>
<middlename>Cody</middlename>
<lastname>Frankenstein</lastname>
</sistername>
</frankenstein>

I would then have a template matching frankenstein, and want in some
place to call the name-formatting template for fathername, in another
place call it for mothername, and in another place call it for
sistername...

this will work with call-template as well. You can also use for-each.
The XPath expressions in for-each will be relative to the node
currently being processed.

Yes, but I need some way to make the child element the current
context for the called template, so that I don't have to redefine
that template many times.

% * How can I logically AND two expressions in an XPath boolean
% expression?

Using `and'.

Thanks, for some reason I missed that in my reference.

% * Can I define more than one template for a match, with one being the
% default, but being able to select different ones with
% xsl:apply-templates? (I understand that modes are only to select
% which elements to process, not which of a few templates to apply to
% an element)

No, modes are to select which of a few templates to apply to an element.
Anyway, there are a few things which might deal with your problem.

OK, I understood that (from the example Martin gave)... Not sure
anymore, but I tried to use it in a similar (but apparently incorrect)
way and misunderstood their purpose afterwards when reading more
about them. Martin's example works.

<snip />

% What I'm right now working on is defining an XSD type for human names:

For a tiny subset of humans (says a guy with two middle names .

Sorry for that ... Well, that's just for some little format I'm
practicing (learning) on. The suffix thingy is not really necessary
either, only gives me more options to try stuff with.

% What I want, is to have in an XSL stylesheet, a few different
% templates for processing a personname, and be able to, in different
% contexts (in the same stylesheet), call different templates for it.

Sounds you want to use a mode to me. Define a template with a mode

OK. But, see the previous example (Frankenstein, father, mother, and
sister), for where the problem is.

Which you would call like this:

<xsl:text>I dined with </xsl:text>
<xsl:call-template name='format-name' mode='anal'>
<xsl:text> last week and I was very interesting.</xsl:text>

Thanks,
-- Tom

 

[Patrick TJ McPhee]

% > You could use a mode specific to that element
% >
% > <xsl:template match='frankenstein'>
% > <xsl:apply-templates mode='child-of-frankenstein'/>
% > <xsl:template>
%
% But how would this help, though?

It depends a lot on what you're trying to do.

% There could be different children
% of frankenstein, with different names (but with the same type/format
% of contents), which I would want to process with the same
% template... The template shouldn't have to know about what names of
% elements it could deal with - when called the context should already
% be within that element...

OK, you could do it like this:

<xsl:template match="*" mode='child-of-frankenstein'>
...
</xsl:template>

This template will be evaluated for each child node of 'frankentsein'.
The context will be set to the node. You could also do it like this:

<xsl:template match="frankenstein/*">
...
</xsl:template>

and leave out the mode attribute of the apply-templates element above.


% Yes, but I need some way to make the child element the current
% context for the called template, so that I don't have to redefine
% that template many times.

This can be done using xsl:for-each and xsl:apply-templates. You could
also assign a node to a parameter before calling the template.