function removeProductCategories( $ruleID = false )
    {
        if ( $ruleID === false )
            $ruleID = $this->ID;
        $ruleID =(int) $ruleID;
        $db = eZDB::instance();
        $db->query( "DELETE FROM ezvatrule_product_category WHERE vatrule_id = $ruleID" );
    }