public function countDataItems( $id = null, $attributes = array() )
    {
        $sum = 0;
        foreach( $this->storageStack as $storageConf )
        {
            $sum += $storageConf->storage->countDataItems( $id, $attributes );
        }
        return $sum;
    }
public function countDataItems( $id = null, $attributes = array() )
    {
        $sum = 0;
        foreach( $this->storageStack as $storageConf )
        {
            $sum += $storageConf->storage->countDataItems( $id, $attributes );
        }
        return $sum;
    }
public function countDataItems ( $ id = null , $ attributes = array ( ) ) { $ sum = 0 ; foreach ( $ this -> storageStack as $ storageConf ) { $ sum += $ storageConf -> storage -> countDataItems ( $ id , $ attributes ) ; } return $ sum ; }
Counts how many items are stored, fulfilling certain criteria.

This method counts how many data items fulfilling the given criteria are
stored overall. Note: The items of all contained storages are counted
independantly and summarized.

@param string $id
@param array $attributes
@return int
Counts how many items are stored fulfilling certain criteria .