Object-Oriented Design

2. 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