Error en la instalación de wiki

Problema:
PHP Fatal error:  Class 'DOMDocument' not found in /var/www/html/mz11sistemas/mediawiki-1.20.0/includes/LocalisationCache.php on line 542, referer: http://wiki.mz11sistemas.com/

Solucion:
yum install php-xml
Restart apache
/etc/init.d/httpd restart