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Analysis and Design
Control Flow Model
The Hatley and Pirbhai extensions focus on the representation and specification
of the control-oriented aspects of the software. Moreover, there exists a large
class of applications that are driven by events rather than data that produce
control information rather than reports or displays, and that process information
with heavy concern for time and performance.
Such an application requires the use of control flow modeling in addition to
data flow modeling. For this purpose, control flow diagram is created. The CFD
contain the same processes as the DFD, but shows control rather than data flow.
Control flow diagrams show how events flow among processes and illustrate those
external events that cause various processes to be activated. The relationship
between process and control model is shown in the figures in the sections Control
Specification and Structure Charts.
Drawing a control flow model is similar to drawing a data flow diagram. A data
flow model is stripped of all data flow arrows. Events and control items are then
added to the diagram a "window" (a vertical bar) into the control specification
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