B.2 Example

In Figure 20, an example is given. The MainPriceService is the price service accessed by the Vending Machine (not shown in figure). It is accessing PriceServiceDiscountA and PriceServiceDiscountB. As each price service can access additional price services, PriceServiceDiscountB is accessing PriceServiceDiscountC and PriceServiceDiscountD.

Note that each communication between the price services is potentially a remote operation and may take some time. Therefore, caching information from different price services may be required in order to have a reasonable response time for the main price service. Cashing strategies are vendor-specific.