软件工程Chapter 05 system modeling.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * Another example Class diagrams The UML does not include a specific notation for this database modeling as it assumes an object-oriented development process and models data using objects and their relationships. When showing the associations between classes, it is convenient to represent these classes in the simplest possible way. Information about attributes and operations are added to define class in detail. As illustrated in the previous page: The name of the object class is in the top section. The class attributes are in the middle section. The operations (called methods in Java and other OO programming languages) associated with the object class are in the lower section of the rectangle. 5.3.2 Generalization Generalization is an everyday technique that we use to manage complexity. The UML has a specific type of association to denote generalization. The generalization is shown as an arrowhead pointing up to the more general class. In a generalization, the lower-level classes are subclasses inherit the attributes and operations from their superclasses. These lower-level classes then add more specific attributes and operations. A generalization hierarchy example: Generalization A generalization hierarchy with added detail 5.3.2 Aggregation A special type of association between classes called aggregation in UML to describe one object (the whole) is composed of other objects (the parts). To show this, we use a diamond shape next to the class that represents the whole. A aggregation example: 5.4 Behavioral models Behavioral models are models of the dynamic behavior of the system as it is executing. What happens or what is supposed to happen when a system responds to a stimulus from its environment are shown here. These stimuli as being of two types: Data Some data arrives that has to be processed by the system. Events Some event happens that triggers system processing. Events may have associated data but this