Design and Use of Industrial Software Architectures

Factory. The abstract factory pattern provides an interface to creating a family of related objects without specifying their concrete classes. Often when using reusable software, such as object-oriented frameworks, selecting one type of component in part of the framework restricts the selection of component types in other parts of the framework. The typical example are user-interface frameworks. When one selects an X-windows component such as a window, one is required to Subject attach(Observer) detach(Observer) notify ConcreteSubject getState for all o in observers o->update subjectState return subjectState Observer update ConcreteObserver update observerState observerState := subject->getState subject observers Transformation of Software Architectures 122/130 Copyright April 1999 by Jan Bosch (Draft version) select all component types from the X-windows sub-hierarchies. If one would explicitly use the names of the component types, this would complicate the use of the software for different platforms or the evolution of the software since changing replacing a component type with an updated one will require the software engineer to replace the name of the component type at all points of usage. When the abstract factory pattern is used, the name of the component type is only used in the factory. In figure 19, the structure of the pattern is shown. Since the abstract factory pattern is only used when instantiating objects, it affects the quality attributes even less than the design patterns discussed earlier. Below, this is discussed in more detail. FIGURE 19. Abstract Factory design pattern • The abstract factory pattern requires more computation for the creation of new components, which affects performance negatively. However, once the component is created, the pattern does not play a role, so the impact on performance is minimal in most systems. • Since explicit references to component types are avoided in the majority of the code and concentrated in the factory components, maintainability is improved. Evolving the system by adding new component types will result in a single point of change, rather than many changed distributed throughout the code. • Reliability, safety and security are not affected by the pattern.