It can be seen that by making effective use of the facilities provided by Presentation Manager, and by following a number of simple guidelines in the design and implementation of applications, it is relatively simple to develop a Presentation Manager application that conforms to module-based object-oriented programming standards, and achieves benefits through reduced development effort and easier application maintenance, due to code reuse and encapsulation.
It must be accepted however, that some deviation from strict object-oriented practice may be necessary in order to preserve other important goals such as the preservation of responsiveness to the end user. Adherence to academic principles should not take precedence over achievement of the required result.
The mapping of data objects into application objects must be approached with great care in the design stage of a Presentation Manager application. Presentation Manager allows the creation of window procedures (application objects) that operate on more than one data object, and of multiple window procedures that operate on the same data object. This practice should be discouraged however, since it reduces the level of encapsulation in the application object, increases the interdependence between application objects, and consequently reduces the benefits attainable through code reuse and containment of change.
Notwithstanding, the Presentation Manager environment affords great opportunity for the development of applications that implement the general principles of the object-oriented approach. A central precept of object-oriented design is the generic nature and consequent reusability of the objects so created. Adherence to guidelines that promote conformance to object-oriented concepts such as data abstraction, encapsulation and polymorphism, in conjunction with the facilities provided by Presentation Manager for object creation, communication and subclassing, and by the OS/2 operating system in the form of dynamic linking, facilitates the development of highly granular, reusable generic objects in the Presentation Manager environment.