public function getVolumeEntry($volumeId = null, $location = null)
    {
        if ($volumeId !== null) {
            $uri = self::VOLUME_FEED_URI . "/" . $volumeId;
        } else if ($location instanceof Zend_Gdata_Query) {
            $uri = $location->getQueryUrl();
        } else {
            $uri = $location;
        }
        return parent::getEntry($uri, 'Zend_Gdata_Books_VolumeEntry');
    }