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Finding and using generic templates
You can do a Web search to find generic templates. MindMap team members generally type in the functionality they're looking for, then the term "generic template" (in quotes), then "XSLT". For example, one of the MindMap team members who wants a generic string replacement template might type the following into Google:
string replace "generic template" XSLT |
This has resulted in a growing library of reusable templates for the MindMap team. (See Resources for more EXSLT links.)
EXSLT consists of a group of extensions to the XSLT language. These extensions have been developed by a group of dedicated XSLT enthusiasts. The underlying architecture consists of generic templates, but there is one caveat: They're often not portable in the way other XSLT templates are because they sometimes (but not always) rely on proprietary extensions and sometimes JavaScript.
An EXSLT function's purpose can range from handling regular expressions to manipulating node sets on the fly (both of which are common wish list items for XSLT developers, and both will be standard features in XSLT 2.0). Which extensions you use generally depend on which XSLT processor you are using. They work if the processor has built-in support for them, which is where the dependency lies. You can't use an extension built for Saxon on MSXML processors, and vice versa, so EXSLT is an attempt to standardize extensions. However, you need to check the EXSLT site (in Resources) to determine if the processor you're using supports a specific extension. Luckily, the site is replete with sample generic templates and examples on how to use them.
The first step in using an EXSLT function is to go to www.exslt.org and look for the extension you want. For example, that Web site has some very handy string manipulation functions, and even a regular expression function. Some of them are also less stable than others. In preparing for this article, I found a number of them that simply didn't work, but the site is pretty reliable about indicating whether or not specific functions can be relied on.
The main trick in using an EXSLT function is to find out
what that function actually is. I refer to EXSLT functions as either a process
defined in a named template, which you then call with a parameter value, or as
an actual function. Take a look, for example at this call to the EXSLT math max
function, which works with the Saxon and Xalan processors (but not MSXML).
<?xml version="1.0" encoding="utf-8"?>
<stylesheet xmlns="http://www.w3.org/1999/XSL/Transform"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:func="http://exslt.org/functions"
xmlns:math="http://exslt.org/math" version="1.0"
extension-element-prefixes="math"
math:doc="http://www.exslt.org/math">
<xsl:output method="html" />
<import href="math.max.function.xsl"/>
<import href="math.max.template.xsl"/>
<xsl:template match="/">
<MaxMachine>
<xsl:call-template name="math:max">
<xsl:with-param name="nodes"
select="MachineName/value" />
</xsl:call-template>
</MaxMachine>
</xsl:template>
</stylesheet>
|
The use of the namespaces is an absolute
requirement because they tell the processor to expect an extension function
defined within the EXSLT library. The nodes parameter assumes an element named
values that contains numbers. If you have string characters, you'll need to parse
those out of the value element first. The result of applying the template will
be the maximum value of all the value elements.
One advantage of generic templates like this is that you just need to know how to call the parameters and where to put your template within the scope of the rest of your document.
Note: Generally, if the site says a specific function is not considered stable, they really mean it.
Many of the templates in the EXSLT library have since found their way, in simplified form, into XSLT 2.0. And as XSLT 2.0 approaches, the MindMap team is nearly breathless with anticipation, because they'll be able to use one of the most powerful string parsing mechanisms available: regular expressions.
Table of contents
- Introduction
- Passing log data into an XML document
- Converting a comma-delimited text file to XML elements
- Building string search routines using XPath 1.0 functions
- Parsing string data to display specific substring-based information
- Making your string search routines and string parsers re-usable templates
- Finding and using generic templates
- Using regular expressions through XSLT 2.0
- Summary and XSLT tricks of the trade
- Download
- Resources
- About the author
