Undefined function. Please Help!

Can someone please help me with this error I keep getting.

Fatal error: Call to undefined function: simplexml_load_file() in /homepages/25/d220261013/htdocs/tester/blog.php on line 7

blog.php

<?php

// define the url that will return the xml
$xml_url = ‘articles.xml’;

// use this function to store the xml tree in a variable
$sxml = simplexml_load_file($xml_url);

// print the content of $sxml
// print_r($sxml);

// if you want to get particular values of the xml tree, use a loop
foreach($sxml->article as $key=>$value)
{
echo ‘<img src="’.$value[‘arts’].’" alt="" />’;
echo ‘<p />’;
echo $value[‘titles’];
echo ‘<br />’;
echo $value[‘dates’];
echo ‘<p />’;
echo $value[‘descriptions’];
echo ‘<br />’;
echo ‘<hr />’;
echo ‘<br />’;
}
?>

articles.xml

<?xml version=“1.0” encoding=“utf-8”?>
<Total_articles>

<article titles=“LJH Interior Design” dates=“July 2008” descriptions=“I have been commissioned by a new client, interior designer Lorna J Higgins, to shoot her latest project. For this large family home in Surrey, Lorna has designed the living room, dining room, family room, master bedroom and the entrance hall.” arts=“blog_art/080701.jpg” />

</Total_articles>