Every computer-based system can be modeled as an information transform using an input-processing-output template. Hatley and Pirbhai [HAT87...
Every computer-based system can be modeled as an information transform using an input-processing-output template. Hatley and Pirbhai [HAT87] have extended this view to include two additional system features—user interface processing and maintenance and self-test processing. Although these additional features are not present for every computer-based system, they are very common, and their specification makes any system model more robust.
Using a representation of input, processing, output, user interface processing, andself-test processing, a system engineer can create a model of system components that sets a foundation for later steps in each of the engineering disciplines.
To develop the system model, a system model template [HAT87] is used. The system engineer allocates system elements to each of five processing regions within the template: (1) user interface, (2) input, (3) system function and control, (4) output, and (5) maintenance and self-test.
Like nearly all modeling techniques used in system and software engineering, the system model template enables the analyst to create a hierarchy of detail. A system context diagram (SCD) resides at the top level of the hierarchy. The context diagram "establishes the information boundary between the system being implemented and the environment in which the system is to operate" . That is, the SCD defines all external producers of information used by the system, all external consumers of information created by the system, and all entities that communicate through the interface or perform maintenance and self-test.
