AJAX can be used for interactive communication with an XML file. A web page can fetch information from an XML file with AJAX technology, e.g when you select an item from a dropdown box.

TITLE: One night only
ARTIST: Bee Gees
COUNTRY: UK
COMPANY: Polydor
PRICE: 10.90
YEAR: 1998

The PHP script loads an XML document, "cd_catalog.xml", runs a query against the XML file, and returns the result as HTML:

<?php
 $q=$_GET["q"];
 $xmlDoc = new DOMDocument();
 $xmlDoc->load("cd_catalog.xml");
 $x=$xmlDoc->getElementsByTagName('ARTIST');
 for ($i=0; $i<=$x->length-1; $i++)
    {
//Process only element nodes
   if ($x->item($i)->nodeType==1)
    {
   if ($x->item($i)->childNodes->item(0)->nodeValue == $q)
     {
     $y=($x->item($i)->parentNode);
     }
   }
 }
 $cd=($y->childNodes);
 for ($i=0;$i<$cd->length;$i++)
   {
//Process only element nodes
  if ($cd->item($i)->nodeType==1)
   {
  echo($cd->item($i)->nodeName);
  echo(": ");
  echo($cd->item($i)->childNodes->item(0)->nodeValue);
  echo("<br />");
    }
 }
 ?>

Information taken from the PHP Tutorials