Using PHP and XSL to Transform XML into Web Content
Intended Audience
Overview
Learning Objectives
Background Information
Definitions
Simplified DocBook
Prerequisites
How it works
- Creating the XML File
- The Simplified DocBook Structure
- Creating the XSL Template
- Fundamental XSL Elements
Putting it all together
- Automatically save the results to a file
- Returning the results as a string
- Providing and returning strings
The Script
About the Author
Intended Audience
This tutorial is for developers who have been looking for ways to use XML to manage web content, and XSL to style and format that content. You should be familiar with XML, and having some experience with XSL would be helpful.Overview
Presenting content is one of the more time consuming and challenging tasks when building a web site. This tutorial looks at taking an XML document and dynamically transforming it into HTML using PHP and XSL. As a practical example, this tutorial is available as XML as well as the XSL stylesheet which transforms it into Zend.com's common tutorial layout.The goal of this tutorial is to demonstrate how to use PHP and XSL to transform an XML document into HTML.
Learning Objectives
In this tutorial you will learn:- An introduction to XML, XSL's technologies and the Simplified DocBook DTD.
- How to use PHP and XSL to transform a XML document into HTML
Background Information
When you're working with a lot of content coming from many different authors (like the Zend.com site itself) you need an efficient way of managing and organizing the content. On the Web, documents often need to be presented in a variety of different formats. XML has grown immensely in popularity for web publishing, because it allows data to be stored in a structured format that is easily transformed into other formats.XSL was created as a tool for transforming XML documents. The core of XSL is made up of three technologies. XSL:T, XPath and XSL-FO. In this tutorial we will be looking only at using XSL:T (templates) and XPath for generating HTML.
Definitions
- XML is a meta language for defining markup languages. For more information on XML see “What is XML?” at XML.com
- XSL (Extensible Stylesheet Language) is used for expressing Stylesheets for XML documents. It is made up of three parts, XSLT (transformations), Xpath, and XML-FO. An XSL document is a well formed XML document, that instructs an XSL processor how to transform an XML document. See, What is XSL? for more information.
- XPath is a language for addressing and accessing parts of an XML document. It was designed to be used by XSL:T. The XPath specification can be found at: http://www.w3.org/TR/xpath, and tutorials can be found at: http://www.w3schools.com/xpath/
- XSL:T - XSL:T is one of the main technologies of XSL. It stands for XSL Transformations and is a language for transforming XML documents into other formats. The XSL:T specification can be found at http://www.w3.org/TR/xslt and tutorials can be found at http://www.w3schools.com/xsl/.
Simplified DocBook
Simplified DocBook is a small subset of the original DocBook XML DTD. While the full DocBook DTD is perfectly adequate to structure content for the web, it can be over kill for short web articles. Simplified DocBook addresses a more limited set of needs and provides a more specific set of elements.Although Simplified DocBook is much smaller than the full DocBook DTD, it is still quite hefty in itself. Simplified DocBook is composed of 106 elements, 525 entities, and 26 notations.
For more information on Simplified DocBook see: http://www.oasis-open.org/docbook/xml/simple/.
Prerequisites
- PHP compiled with XML and XSL support
- A Simplified DocBook source file
- An XSL Document
How it works
Creating the XML File
Writing articles in a mark up language is time consuming and can be quite a painful process. Having the right tools can take some of the effort out of creating structured documents. For example: I wrote the content of this tutorial in Open Office's Writer, and then structured it into XML with XMLEditor by XMLmind.com, when it was ready to be published.The advantage of using an XML tool to assist in the structuring is that the final document is less prone to human error. Most XML tools provide faculties for automatically formatting and spacing the XML tags, as well as checking the validity of the document.
XML Editor can be found at: http://www.xmlmind.com/
The Simplified DocBook Structure
Although the Simplifed DocBook is only a small part of DocBook, it can still be a little overwhelming to those unfamiliar with it. This section provides an introduction to the structure of Simplifed DocBook.
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD Simplified DocBook XML V4.1.2.5//EN"
"http://www.oasis-open.org/docbook/xml/simple/4.1.2.5/sdocbook.dtd">
<article>
<title>A Short Example</title>
<section>
<title>Section #1</title>
<para>A short example of a Simplified DocBook file.</para>
</section>
</article>
<article> and
<section>. Other elements, such
as <para>,
<example>,
<itemizedlist>, etc. describe
different things within the document.In Simplified DocBook the root element is always
<article>. Articles can be
separated into sections, and each sections can contain an unlimited number of
sub-sections. The most common types of element are titles, paragraphs, links,
and lists. For a full listing of elements see
Simplified DocBook: The Definitive Guide.Creating the XSL Template
The purpose of the XSL template we will be creating in this tutorial is to transform the Simplified DocBook structured data into Zend.com's standard tutorial format. The standard layout for their tutorials are:- Title of tutorial
- Date of article
- Name of author
- Table of Contents
- Intended Audience
- OverviewLearning
- Objectives
- Definitions
- Background
- Information
- Prerequisites
- How it works
- The Example Script
Here is an example of an XSL Template to transform the minimal example above:
<xml version='1.0'?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version='1.0'>
<xsl:output method="html"/>
<xsl:template match="/">
<html>
<head><title><xsl:value-of select="title"/></title></head>
<body>
<xsl:apply-templates/>
</body>
</html>
</xsl:template>
<xsl:template match="article/title">
<h1><xsl:value-of select="."/></h1>
</xsl:template>
<xsl:template match="section">
<xsl:apply-templates/>
</xsl:template>
<!-- Formatting for JUST section titles -->
<xsl:template match="section/title">
<h2><xsl:value-of select="."/></h2>
</xsl:template>
<xsl:template match="para">
<P><xsl:apply-templates/></P>
</xsl:template>
</xsl:stylesheet>
<xsl:stylesheet>, and it is
usually made up of <xsl:output>,
<xsl:template>,
<xsl:apply-templates> and
<xsl:value-of>. There are a few
more useful elements but those four are essential to providing the core
functionality.Fundamental XSL Elements
|
<xsl:output> |
This element defines the format of the output document. The
allowed methods are xml, html, text and name. |
|
<xsl:template> |
An XSL Stylesheet consists of a set of templates. These
templates contain rules that are applied when a specific matching node is found.
Template element structure is quite simple. At the most basic level they simply
replace the element they match with whatever is in the template. From the above
example when <xsl:template
match=”article/title”> is matched, the XML
<title>A Short
Example</title> turns into HTML
as, <h1>A Short
Example</h1>. To correctly match a template to a single node
or a set of nodes, XPath is used. In the above example,
<xsl:template
match=”para”> matches any
<para> element within the
document. If the template element read,
<xsl:template
match=”article/para”> then only
<para> elements directly beneath
<article> will be
matched. |
|
<xsl:apply-templates> |
This element instructs the XSL processor to apply matching
templates to the current element, or the current element's child
nodes. |
|
<xsl:value-of> |
This element extracts the value of a selected node. |
There are a few other common and useful elements, such as
<xsl:if>
and <xsl:choose> which allows testing of conditions before
applying rules, <xsl:for-each> which allows looping through
elements, and <xsl:sort> which allows sorting of output.
Putting it all together
Performing XSL transformations in PHP is very simple. The hardest part of using XSL in PHP is creating the actual transformation file.With XML and XSL documents, transformation using PHP consists of two steps: The first step is to create the XSL:T processor with
xlst_create(); the second is to use
xlst_process() to transform the XML
into HTML.
The
xslt_process() function handles all the transformation work.
There are three different ways of using xslt_process(). The examples
below are from the PHP Manual.
Method 1: Automatically save the results to a file
<?php
// Allocate a new XSLT processor
$xh = xslt_create();
// Process the document
if (xslt_process($xh, 'sample.xml', 'sample.xsl', 'result.xml')) {
print "SUCCESS, sample.xml was transformed by sample.xsl into result.xml";
print ", result.xml has the following contents\n<br>\n";
print "<pre>\n";
readfile('result.xml');
print "</pre>\n";
}
else {
print "Sorry, sample.xml could not be transformed by sample.xsl into";
print " result.xml the reason is that " . xslt_error($xh) . " and the ";
print "error code is " . xslt_errno($xh);
}
xslt_free($xh);
?>
Method 2: Returning the results as a string
(In most cases this method is more useful.)
<?php
// Allocate a new XSLT processor
$xh = xslt_create();
// Process the document, returning the result into the $result variable
$result = xslt_process($xh, 'sample.xml', 'sample.xsl');
if ($result) {
print "SUCCESS, sample.xml was transformed by sample.xsl into the \$result";
print " variable, the \$result variable has the following contents\n<br>\n";
print "<pre>\n";
print $result;
print "</pre>\n";
}
else {
print "Sorry, sample.xml could not be transformed by sample.xsl into";
print " the \$result variable the reason is that " . xslt_error($xh) .
print " and the error code is " . xslt_errno($xh);
}
xslt_free($xh);
?>
Method 3: Providing and returning strings
The third way of usingxslt_process()
is to provide the XML and XSL documents as string values, and have the function
return a string value. This method is the most flexible as you can do some pre-processing
and post-processing to the XML or XSL documents before passing them to the processor.
<?php
// $xml and $xsl contain the XML and XSL data
$arguments = array(
'/_xml' => $xml,
'/_xsl' => $xsl
);
// Allocate a new XSLT processor
$xh = xslt_create();
// Process the document
$result = xslt_process($xh, 'arg:/_xml', 'arg:/_xsl', NULL, $arguments);
if ($result) {
print "SUCCESS, sample.xml was transformed by sample.xsl into the \$result";
print " variable, the \$result variable has the following contents\n<br>\n";
print "<pre>\n";
print $result;
print "</pre>\n";
}
else {
print "Sorry, sample.xml could not be transformed by sample.xsl into";
print " the \$result variable the reason is that " . xslt_error($xh) .
print " and the error code is " . xslt_errno($xh);
}
xslt_free($xh);
?>
The Script
The following script demonstrates how post-processing can be applied after the XML document has been transformed. After the document has been transformed, PHP looks for special delimiters in the HTML, which designate different languages (ie. php), and run them through syntax highlighting.
<?php
function unhtmlentities ($string)
{ // FROM PHP Manual
$trans_tbl = get_html_translation_table (HTML_ENTITIES);
$trans_tbl = array_flip ($trans_tbl);
return strtr($string, $trans_tbl);
}
// $xml and $xsl contain the XML and XSL data...
$xml = implode('',file('document.xml'));
$xsl = implode('',file('sdocbook.xsl'));
$xh = xslt_create();
$output = xslt_process($xh, 'arg:xml', 'arg:xsl', NULL,
array(
'xml' => $xml,
'xsl' => $xsl));
/* Find all the little parts that need to be highlighted.
.. the XSL transformation process puts in tags like
<parse_php>, <parse_xsl>, <parse_xml>... etc.
*/
$types = array('php'); // add more to this array as we find better highlighters
foreach ($types as $type) {
$oKey = "<parse_$type>";
$cKey = "</parse_$type>";
$outputArray = explode($cKey,$output);
unset($outputArray[count($outputArray)-1]); // drop the data at the end.
foreach ($outputArray as $data) {
$data = substr($data,strpos($data,$oKey)+strlen($oKey));
switch ($type) { // do the highlighting...
case 'php':
$dataReplace = unhtmlentities($data);
$dataReplace = highlight_string($dataReplace,true);
break;
}
// replace the data in output..
$output = str_replace("$oKey$data$cKey",$dataReplace,$output);
}
}
echo $output; // print output
?>
About the Author
Benson Wong is a programmer and a system administrator. As the head of Tummy Tech's technology department, Benson often has to be a Swiss army knife of technical knowledge. While most of his time is spent working with his programming team, Benson occasionally works with his network and system administration team to develop new procedures for streamlining the technical requirements of their clients. When not at the office, Benson is building the electronic music community beatmatch.com and working on his martial arts training.Benson can be contacted at phpauthor@tummytech.com.
Comments
Your first xsl example has a litle bug. The first ? character is missing from the first line. Please update this tutorial. For beginners it's hard to figuring out the reason of the error messages.
My second problem is with xslt_create() function call. I switched on in my ZendCore admin all xml and xsl related modules, but the example failed with error. I think some advices for modul install should be very useful.
I solved the problem with replacing the php code with an other xsl example using DOMDocument(), XSLTProcessor() objects.
Otherwise the tutorial was wery useful, thx!
Tama's