protected function _extractSequence($file)
    {
        $sequence = '';
        $hlpr = Mage::helper('radial_core');
        $domDocument = $hlpr->getNewDomDocument();
        // load feed files to dom object
        $domDocument->load($file);
        $feedXpath = $hlpr->getNewDomXPath($domDocument);
        $correlationId = $feedXpath->query('//MessageHeader/MessageData/CorrelationId');
        if ($correlationId->length) {
            $sequence = (string) $correlationId->item(0)->nodeValue;
        }
        return $sequence;
    }