System analysis and design course- System Design chapter

Question

Question is here: "Program Design presents your final structure chart. Start with physical data flow diagrams (DFD). Modify your logical DFDs by adding implementation references, human-machine boundary and system-related elements."

I have my level 0 DFD and the project is about fixing anything damaged at home or in company. So how can i do this task?

Answer 1

Just follow the principles laid down by either Tom Demarco from Yourdon Inc in his book "Structured Analysis and Design Technique" (1979) or Chris Gane and Trish Sarson in their book "Structured system analysis" (1979):

• start with your level 0 diagram
• take all the processes identified in one level and decompose each of them into further sub-processes to get the next level
• continue until the level of detail is sufficient
• at the same time, maintain a data dictionary describing more precisely the content of the named data flows in the diagram, and decompose them further as more details get known.

Looking at your instructions:

• Users are represented as external entity squares. Flows between processes and external entities representing humans correspond to human-machine boundary
• the data dictionary should correspond at the most detailed level to your file or database structure; a clear mapping should be feasible;
• the processes at the most detailed level should be implementable in a program/app, or a programme function, and you should be able to have a clear mapping.