PATTERNS OF DATA MODELING- P43: Models provide the means for building quality software in a predictable manner. Models let developers think deeply about software and cope with large size and complexity. Developers can think abstractly before becoming enmeshed in the details of writing code. Although models are beneficial, they can be difficult to construct. That is where patterns come in. Patterns provide building blocks that help developers construct models faster and better. | Chapter Summary 197 Chapter Summary This chapter presents a model of generic diagrams. A generic diagram appears as a picture but has semantic content that lies behind the graphics. The model is too large to fit on a single page so the chapter divides the model into four subject areas. The generic diagram model provides a starting point for various kinds of diagrams such as data structure diagrams data flow diagrams state diagrams and equipment flow diagrams. I have used the technology in this chapter on several consulting projects. Bibliographic Notes This chapter is motivated by my personal experiences with consulting projects. The following notions have been especially useful in practice. The uniform mapping of diagram constructs to model constructs. The ability to hierarchically nest diagrams and models. The ability to display graphical constructs based on the type of diagram. The ability to include or omit ports and tabs. 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 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 approval the order is considered complete. The product is then shipped and the customer signs for delivery. This completes order processing and the order is considered fulfilled. One way to realize state diagrams is by writing the equivalent procedural code. Another option is to have a generalized .
