Software Engineering-Object Oriented Design


Object-oriented design transforms the analysis model created using object-oriented analysis into a design model that serves as a blueprint for software construction. Yet, the job of the software designer can be daunting. Gamma and his colleagues  provide a reasonably accurate picture of OOD when they state:

Designing object-oriented software is hard, and designing reusable object-oriented software is even harder. You must find pertinent objects, factor them into classes at the right granularity, define class interfaces and inheritance hierarchies, and establish key relationships among them. Your design should be specific to the problem at hand but also general enough to address future problems and requirements. You also want to avoid redesign, or at least minimize it. Experienced object-oriented designers will tell you that a reusable and flexible design is difficult if not impossible to get "right" the first time. Before a design is finished, they usually try to reuse it several times, modifying it each time.

Unlike conventional software design methods, OOD results in a design that achieves a number of different levels of modularity. Major system components are organized into subsystems, a system-level “module.” Data and the operations that manipulate the data are encapsulated into objects—a modular form that is the building block of an OO system. In addition, OOD must describe the specific data organization of attributes and the procedural detail of each individual operation. These represent data and algorithmic pieces of an OO system and are contributors to overall modularity.

The unique nature of object-oriented design lies in its ability to build upon four important software design concepts: abstraction, information hiding, functional independence, and modularity . All design methods strive for software that exhibits these fundamental characteristics, but only OOD provides a mechanism that enables the designer to achieve all four without complexity or compromise. Object-oriented design, object-oriented programming, and object-oriented testing are construction activities for OO systems.
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