Presentation Manager facilitates the implementation of an event-driven, object-action user interface and provides predefined constructs that enable a consistent, intuitive user interface for multiple applications, in line with the objectives of the Systems Application Architecture Common User Access component. However, in order to gain the fullest benefit from such an interface, the application developer must adopt a certain degree of object-oriented principles in the design and implementation of applications.
In order to support the implementation of an event-driven interface and facilitate the incorporation of object-oriented design techniques, Presentation Manager provides an object-based, event-driven execution environment with an application architecture that conforms closely to object-oriented theory, within the framework of the Systems Application Architecture Common Programming Interface. Windows become the handles by which the application references data objects, and windows communicate with one another and with the user in an event-driven manner. With the addition of the Workplace Shell in OS/2 Version 2.0, the user and the programmer may deal directly with objects and take full advantage of the concept of inheritance.
Benefits to be gained from the adoption of such principles include enhanced opportunity for code reuse with consequent reductions in development costs, and easier containment of change through encapsulation and data isolation. As the programmable workstation becomes more widely utilized as the platform for line-of-business applications, the importance of sound software engineering principles in the design and implementation of workstation applications will increase, in accordance with the requirement to be able to adequately manage and maintain these applications. OS/2 and Presentation Manager together with the Workplace Shell, which extends the paradigm to further exploit object-oriented concepts, provide a platform for the implementation of such principles.
It must be emphasized that Presentation Manager provides an application architecture at the operating system level which supports the implementation of certain object-oriented software engineering principles, and provides many of the facilities required by such an approach. However, while Presentation Manager supports an object-oriented approach to application design, it does not force the application developer to conform to object-oriented design practices. Presentation Manager does not provide, nor does it seek to provide, a complete development environment for object-oriented applications; the provision of such function is the responsibility of application-enabling products that may reside and execute in the Presentation Manager environment.
The remainder of this document will further explore the relationship between OS/2 Version 2.0, Presentation Manager and object-oriented programming, and examine the techniques by which object-oriented applications may be implemented in the Presentation Manager environment, using both the Presentation Manager and Workplace Shell application models.