Data flow diagram (DFD) is used to show how data flows through the system and the processes that transform the input data into output. Data flow diagrams are a way of expressing system requirements in a graphical manner. DFD represents one of the most ingenious tools used for structured analysis. It is also known as a bubble chart.
In the normal convention, logical DFD can be completed using only four notations.
The DFD at the simplest level is referred to as the ‘CONTEXT ANALYSIS DIAGRAM’. These are expanded by level, each explaining its process in detail. Processes are numbered for easy identification and are normally labeled in block letters. Each data flow is labeled for easy understanding.
Steps to Construct Data Flow Diagrams
Four steps are commonly used to construct a DFD
- Process should be named and numbered for easy reference. Each name should be representative of the process.
- The direction of flow is from top to bottom and from left to right.
- When a process is exploded in to lower level details they are numbered.
- The names of data stores, sources and destinations are written in capital letters.
Salient feature of DFD
Q The DFD shows flow of data, not of control loops and decision are controlled considerations do not appear on a DFD.
Q The DFD does not indicate the time factor involved in any process whether the data flows take place daily, weekly, monthly or yearly.
Q The sequence of events is not brought out on the DFD.
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