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.
Object-Oriented Design Activities
In ABC's rental application, we are using off-the-shelf software in an off-the-shelf hardware environment. In the environment, the operating system, network, database, and form of human interface are all given. Because of our choices-PCs, MS-DOS, Novell Netware, and a SQL DBMS-the application does not easily lend itself to object-oriented design that assumes none of the services and functions provided in our target environment. Because of the differences, we will discuss ABC at two levels: one for SQL DBMS which becomes unobject-like, and one for a Unix/C++ environment that stays object-like. First, we follow ABC through the process of design keeping in mind that the off-the-shelf software will be used. Think of this design as object-based, that is, based on object thinking, but decidedly not object-oriented in implementation. Object-based design is what is practiced by most novice object-designers, and is what most CASE tools being retrofitted for object orientation will be. In the chapter appendix, we present a second design for a Unix/c++ environment that is completely object-oriented. Without both discussions, the view of object orientation that you would get is not complete, and some of the discussions would be inaccurately stated for object-oriented design.