Association information can be used in several ways. When a customer buys a
particular book, an online shop may suggest associated books. A grocery shop
may decide to place bread close to milk, since they are often bought together, to
help shoppers finish their task faster. Or, the shop may place them at opposite
ends of a row, and place other associated items in between to tempt people to buy
those items as well, as the shoppers walk from one end of the row to the other. A
shop that offers discounts on one associated item may not offer a discount on the
other, since the customer will probably buy the other anyway.