public function countDataItems( $id = null, $attributes = array() )
    {
        if ( !isset( $this->clusterCacheFile ) )
        {
            $this->clusterCacheFile = eZClusterFileHandler::instance(
                $this->properties['location'] . $this->generateIdentifier( $id, $attributes )
            );
        }

        return $this->clusterCacheFile->exists() ? 1 : 0;
    }