protected static function _generateGuid($prefix = 'pfx')
{
$uuid = md5(uniqid(rand(), true));
$guid = $prefix . substr($uuid, 0, 8) . "-" . substr($uuid, 8, 4) . "-" . substr($uuid, 12, 4) . "-" . substr($uuid, 16, 4) . "-" . substr($uuid, 20, 12);
return $guid;
}