What is a DFD?

• A Data Flow Diagram called DFD is a graphical representation of the "flow" of data.
• DFD depicts the flow of data from external entities to the system.
• As the name suggests it shows how data moved from one process to another.
• It also needs to tell details of logical storage.
• By examining DFD we should be able to identify the process, flows, stores and external entities in a system.
• It also gives details of Data into the system

How to design Data Flow Diagram?

We need to make use of various symbols while designing DFD

• Squares  depicts  external entities, it can be either  are source or destination of data.
• Rounded rectangles depicts processes. The process is the one that takes data as input, perform some operations and gives output .
• Arrows  depicts the data flows.
• Open-ended rectangles depicts data stores.

After getting the requirement we need to identify external entities , processes ,data flows and data stores in the system. Then draw the flow accordingly.

When to use what ?

These are the strict rules to be followed while designing DFDs

1. All processes must have at least one data flow in and  out.

2. All processes should modify the incoming data, producing some outgoing data.

3. Every  data store and external entity  must be entailed in at least one data flow.

4. A data flow must be attached to one process at least.

Pros of DFD

• It gives detailed absorption of the system and its sub-systems if any
• It is useful for the communication flow of current system awareness.
• It can also be Used as part of the system documentation files
• It gives the abstraction of the system or component
• DFD is useful for quick reference to the development team

Cons of DFD

• DFD is may take many alteration before agreement with the client