Design Steps

The given example will be used to demonstrate each step in transform mapping the steps start with a re- evaluation of work done during requirements analysis and then move to the development of program structure.

Step 1.  By Review the fundamental system model.  Fundamental system model encompasses the level zero Data Flow Diagram and supporting information.   In reality the design step starts with an evaluation of both the system specification and the software needs specification.  Both documents define structure and information flow at the software interface. In the Figure 20.3, 20.4 depict level zero and level one data flow for the Safe Home software.

Step 2.  By Review and refine data flow diagrams for the software. The Information obtained from analysis models contained in the software requirements specification   is sophisticated to produce greater detail.   Example For, the level DFDs for monitor sensors are examined and a level three data flow diagram is derived as describe in figure 20.6.    At  level three  each  transform  in  the  data  flow  diagram  exhibits  relatively high cohesion in last chapters.   Which is the process implied through a transform performs a single and distinct function which can be implemented as a module in the Safe Home software.  Thus, the Data Flow Diagram in figure 20.6 contains sufficient detail for a first cut at the design of program structure for the monitor sensors.Subsystem and we proceed without future refinement.