The invention helps an on-line shopper maintain the proper relationship between primary items in a shopping cart and secondary items in the shopping cart, where secondary items are items that normally accompany the purchase of primary items. The server that provides the on-line shopping service awaits a shopper's commands. When a command is detected that indicates a change in an attribute of a primary item, the server checks the shopper's shopping cart to identify secondary items linked to the primary item whose attribute was changed. If a secondary item linked to the primary item is identified, the server then solicits the shopper's authorization to change a corresponding attribute of the secondary item. If the shopper grants authorization, the server changes the corresponding attribute of the secondary item accordingly. An item's attribute may be the quantity of the item in a shopping cart, the size of the item, the color of the item, the texture of the item, and so forth.