Object-Oriented Design
The text uses the Booch (1991) methodology to illustrate object-oriented design. The result of object-oriented analysis is translated into time-event diagrams, Booch diagrams, message communications, service objects, and process diagrams. Collectively, they constitute a set of holistic specifications to effectively allocate functionality over program modules at the lowest level and multiprocessor configurations at the highest level.
The Booch notation has been unified with other object-oriented notations (Rumbaugh and Jacobsen) into Unified Modeling Language (UML). In Unit 10, we will look at another example of object-oriented analysis and design using the UML notation. Therefore, you may skim this chapter to gain familiarity with OOD, which you will apply in Unit 10.
Conceptual Foundations
Encapsulation and inheritance are the basis for OOD, just as they were for object-oriented analysis. In addition, the scope of the thinking process is expanded. The design approach is holistic, designing, people, hardware, software, and data as the four components of object-oriented systems. As figure 12-1 shows, the four components all relate to each other and can all communicate with each other. This design methodology makes a valuable contribution to methodological thinking by integrating the components, many of which are frequently ignored. As multiprocessor computing, such as in client/server, increases, this type of classification will be required of any methodology. Object method developers have led the thinking about multiprocessor applications because of the closeness between object-oriented applications and operating systems from which many concepts are borrowed.
OOD explicitly uses an iterative approach to detailed design that Booch calls "round-trip gestalt", meaning the incremental development of whole applications. Each prototype is the entire application as currently defined. As the prototype is examined, further details of operation are explicated for incorporation in the next iteration of the prototype. Following the format of previous chapters, we first define terms used in the OOD process, then move on to developing guidelines for each step and an example of the step and thinking processes for ABC Video's rental application.
FIGURE 12-1 Object-Oriented Subdomains