I am making a DFD diagram for software that is going to run on a PLC to control a testing setup.In this setup i have 7 load cells and 7 hydraulic valves.
I am wondering if i need to show all 7 of them or just one. doing it with just one looks a lot cleaner. See below for examples.
The 2 ways i tried:
The diagram is a bit more complex but i am showing this for simplicity.
I have tried both examples shown aboec but i am not sure which one to use. can somebody give me some advice?
Thanks already
Chris Gane & Trish Sarson's defined in their pioneering book "Structured system analysis" external entities in DFDs (page 26):
External entities are most usually logical classes of things or people which represent a source or a destination of data, e.g. customers, employees, aircraft (...). They may also be a specific source or destination e.g. Accounts department, IRS, Office of the president (...).
This book laid the foundation to the Gane&Sarson DFD diagramming, and is one of the leading original reference of DFD (together with Tom DeMarco from Yourdon Inc.).
The authors show multiple example diagrams where one external entity symbol represents a class of many external entities, like Customer or Employee, sometimes spelled in the plural as Customers sometimes in the singular.
So the clear answer is to use the second simplified diagram, with Valves and Load cells preferably in plural as you did. There is no multiplicity notation in DFD, but nothing prevents you from making an informal annotation/comment on the diagram.
The first diagram is not wrong, each rectangle representing a specific valve or cell, but we agree that it's cumbersome. For 7 it's still ok, but imagine you had 200...
