Creating structural business rules at the outset will help guide the design throughout the rest of the sections. An example of this type of business rule not related to Amazon is A car may be driven by many drivers; each driver drives one or more cars. Each business rule should describe the entities involved, the relationship between the entities, and the optionality and plurality constraints for each entity. Try to make sure that you have created all the structural business rules required for each use case.

Use Case 4 - Product Purchase by Consumer

This occurs when a consumer purchases a product from Amazon that was provided by a seller:

1. The consumer logs in to Amazon under their account.
2. The consumer selects one or more products on Amazons website. When selecting a product, the consumer is actually selecting a particular sellers inventory, though they might not realize this because the process is seamless on Amazons website.
3. The consumer selects a shipping speed (super saver shipping, standard shipping, twoday, oneday) and finalizes their choices.
4. Amazon decrements the sellers inventory for the products purchased.
5. Amazon creates an order which tracks which consumer purchased which products from which sellers.