Good things come in twos: Mickey and Donald, Tom and Jerry, yin and yang. It's no surprise then that XML_Serializer has a doppelganger of its own. Called XML_Unserializer, this class can take an XML document and convert it into a series of nested PHP structures, suitable for use in a PHP script.

In order to understand how this works, consider the following XML document:


<?xml version='1.0'? >
<library>
 <book id="MFRE001">
  <title>The Adventures of Sherlock Holmes</title>
  <author>Arthur Conan Doyle</author>
  <price currency="USD">24.95</price>
 </book>
 <book id="MFRE002">
  <title>Life of Pi</title>
  <author>Yann Martel</author>
  <price currency="USD">7.99</price>
 </book>
 <book id="MFRE003">
  <title>Europe on a Shoestring</title>
  <author>Lonely Planet</author>
  <price currency="USD">16.99</price>
 </book>
</library>



Now, in order to convert this XML document into a PHP structure, simply put XML_Unserializer to work on it, as below:


<?php
 
// include class file
include("Unserializer.php");
 
// create object
$unserializer = &new XML_Unserializer();
 
// unserialize the document
$result = $unserializer->unserialize("library.xml", true);    
 
// dump the result
$data = $unserializer->getUnserializedData();
print_r($data);
 
? >



Here, the unserialize() method accepts either a string containing XML data or an XML file (set the second argument to false or true depending on which one you are passing) and returns a PHP structure representing the XML document. Here's what the output looks like:


Array
(
    [book] => Array
        (
            [0] => Array
                (
                    [title] => The Adventures of Sherlock Holmes
                    [author] => Arthur Conan Doyle
                    [price] => 24.95
                )
 
            [1] => Array
                (
                    [title] => Life of Pi
                    [author] => Yann Martel
                    [price] => 7.99
                )
 
            [2] => Array
                (
                    [title] => Europe on a Shoestring
                    [author] => Lonely Planet
                    [price] => 16.99
                )
        )
)



Now, in order to access the title of the third book (for example), you would use the notation


$data['book'][2]['title'];



which would return

Europe on a Shoestring

Note that XML_Unserializer uses the type hints generated in the serialization process to accurately map XML elements to PHP data types. If these hints are unavailable (as in the example above), XML_Unserializer will "guess" the type of each value. A look at the source code of the class reveals that "complex structures will be arrays and tags with only CData in them will be strings."