Types & Conversion of Data Flow Diagrams

Physical and Logical DFDs:

There are mainly two types of Data Flow Diagrams namely Physical DFD and Logical DFD.Here is some information which might help you to distingush between two of them:

Physical DFD:

An Implementation dependent view of your system which shows what tasks are to be carried out and how are they they carried out.It may include:

  • Names of people,procedure,departments
  • Form and document names or numbers
  • Master and transaction files
  • Equipment and device used
  • Locations

Logical DFD:

An Implementation independent view of your system which will just focus on the flow of the data between the processes regardless to their storage devices,storage locations or people in the system.None of the characteristics defined above for physical DFD will be included in Logical DFDs.


Conversion from Physical DFD -> Logical DFD

A logical DFD will provide you the basics for examining the combination of process,data flows,data stores,input and outputs involved in the system without concerning with the physical devices,people or any other controlling factor that characterise the implementation part.

Steps for converting Physical DFD into Logical DFD:
  1. Directly show the actual data needed in a process,not the documents that contain them.
  2. Only show the flows between the processes. Remove all other routing informations such as flow between the people,office etc.
  3. Remove reference to physical devices.
  4. Remove reference to controlling factors.
  5. Remove unnecessary processes i.e. the process which do not affect on data or data flows.

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