public function isOld($key, $config)
    {
        if (substr_count($key, ',') < 2) {
            return true;
        }
        list($version, $hash, $revision) = explode(',', $key, 3);
        $compare = version_compare($version, $config->version);
        // version mismatch, is always old
        if ($compare != 0) {
            return true;
        }
        // versions match, ids match, check revision number
        if ($hash == $config->getBatchSerial($this->type) &&
            $revision < $config->get($this->type . '.DefinitionRev')) {
            return true;
        }
        return false;
    }