Patterns of Data Modeling

Chapter 15

State Diagrams

A state diagram specifies states and stimuli that cause changes of state. State diagrams are often used for control and managing user interaction. They are also helpful for enforcing business policies and constraining data — the reason for coverage in this chapter.

Figure 15.1 shows a simple state diagram for processing orders. A customer places an order and it is quickly acknowledged. Some further processing assigns a customer number and order number and the order is then confirmed. The desired product may or may not be available. If inventory is lacking, the order can be back ordered or if the customer cannot wait, the order is cancelled. Once inventory is available, the customer’s payment is processed. Upon payment ...