SOFTWARE PROCESS MODELS - Incremental Model, Spiral Model, WINWIN Spiral Model, Concurrent Development Model
Object-oriented technologies provide the technical framework for a component-based process model for software engineering. The objectoriented paradigm emphasizes the creation of classes that encapsulate both data and the algorithms used to manipulate the data. If properly designed and implemented, object-oriented classes are reusable across different applications and computer-based system architectures.
The component-based development (CBD) model (Figure 2.11) incorporates many of the characteristics of the spiral model. It is evolutionary in nature [NIE92], demanding an iterative approach to the creation of software. However, the component-based development model composes applications from prepackaged software components (called classes).
The engineering activity begins with the identification of candidate classes. This is accomplished by examining the data to be manipulated by the application and the algorithms that will be applied to accomplish the manipulation. Corresponding data and algorithms are packaged into a class.
Classes created in past software engineering projects are stored in a class library or repository. Once candidate classes are identified, the class library is searched to determine if these classes already exist. If they do, they are extracted from the library and reused. If a candidate class does not reside in the library, it is engineered using object-oriented methods (Chapters 21–23). The first iteration of the application to be built is then composed, using classes extracted from the library and any new classes built to meet the unique needs of the application. Process flow then returns to the spiral and will ultimately re-enter the component assembly iteration during subsequent passes through the engineering activity.
The component-based development model leads to software reuse, and reusability provides software engineers with a number of measurable benefits. Based on studies of reusability, QSM Associates, Inc., reports component assembly leads to a 70 percent reduction in development cycle time; an 84 percent reduction in project cost, and a productivity index of 26.2, compared to an industry norm of 16.9. [YOU94] Although these results are a function of the robustness of the component library, there is little question that the component-based development model provides significant advantages for software engineers.
The unified software development process [JAC99] is representative of a number of component-based development models that have been proposed in the industry. Using the Unified Modeling Language (UML), the unified process defines the components that will be used to build the system and the interfaces that will connect the components. Using a combination of iterative and incremental development, the unified process defines the function of the system by applying a scenario-based approach (from the user point of view). It then couples function with an architectural framework that identifies the form the the software will take.