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XML is a markup language that looks a lot like HTML. An XML document is plain text and contains tags delimited by < and >.There are two big differences between XML and HTML:

• XML doesn't define a specific set of tags you must use.

• XML is extremely picky about document structure.

XML gives you a lot more freedom than HTML. HTML has a certain set of tags: the <a></a> tags surround a link, the <p> startsa paragraph and so on. An XML document, however, can use any tags you want. Put <rating></rating> tags around a movie rating, >height></height> tags around someone's height. Thus XML gives you option to device your own tags.

XML is very strict when it comes to document structure. HTML lets you play fast and loose with some opening and closing tags. BUt this is not the case with XML.

HTML list that's not valid XML:

<ul>
<li>Braised Sea Cucumber
<li>Baked Giblets with Salt
<li>Abalone with Marrow and Duck Feet
</ul>

This is not a valid XML document because there are no closing </li> tags to match up with the three opening <li> tags. Every opened tag in an XML document must be closed.

HTML list that is valid XML:

<ul>
<li>Braised Sea Cucumber</li>
<li>Baked Giblets with Salt</li>
<li>Abalone with Marrow and Duck Feet</li>
</ul>

Parsing an XML Document:

PHP 5's new SimpleXML module makes parsing an XML document, well, simple. It turns an XML document into an object that provides structured access to the XML.

To create a SimpleXML object from an XML document stored in a string, pass the string to simplexml_load_string( ). It returns a SimpleXML object.

Example:

Try out following example:

<?php

$channel =<<<_XML_
<channel>
<title>What's For Dinner<title>
<link>http://menu.example.com/<link>
<description>Choose what to eat tonight.</description>
</channel>
_XML_;

$xml = simplexml_load_string($channel);
print "The $xml->title channel is available at $xml->link. ";
print "The description is \"$xml->description\"";
?>

It will produce following result:

NOTE: You can use function simplexml_load_file( filename) if you have XML content in a file.

Generating an XML Document:

SimpleXML is good for parsing existing XML documents, but you can't use it to create a new one from scratch.

The easiest way to generate an XML document is to build a PHP array whose structure mirrors that of the XML document and then to iterate through the array, printing each element with appropriate formatting.

Example:

Try out following example:

<?php

$channel = array('title' => "What's For Dinner",
                 'link' => 'http://menu.example.com/',
                 'description' => 'Choose what to eat tonight.');
print "<channel>\n";
foreach ($channel as $element => $content) {
   print " <$element>";
   print htmlentities($content);
   print "</$element>\n";
}
print "</channel>";
?>

It will produce following result:

<channel>
<title>What's For Dinner</title>
<link>http://menu.example.com/</link>
<description>Choose what to eat tonight.</description>
</channel></html>