Data Flow Diagram - Validating DFD


Validating the DFD

Before moving on from this initial high-level DFD, we must ensure it is consistent. Below is a checklist of points to watch out for before moving on to a detailed investigation which will take us to lower levels.

1.   Has each process a strong imperative verb and object?
2.   Are data flows in related to data flows out? Data should not be swallowed up by a process, only transformed in some way. A data store is the only place data is allowed to rest. Similarly, data cannot be generated by a process. A document may be, but the data on the document comes from a data flow into that process.
3.   Can the flows be reduced? If a process is too busy, it can perhaps be broken down into two or more processes: six data flows in or out of a process should be enough.
4.   Do all data stores have flows both in and out? A one-way data store is of little use, unless it is a reference file. If the Current Physical DFD should identify such a data store, confirm with the User that you have correctly understood the procedures.
5.   Are symbols correctly labelled and uniquely referenced?
6.   Do all external entities communicate with a process? No entity should be allowed direct access to data, either to read or to update it.

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