Data Flow Diagram (DFD)

The Data Flow Diagram (DFD) is a simple graphical notation that can be used to represent a system in terms of the input data to the system. It is also known as "Bubble Chart".
The following are the basic element of DFD.

External Entity

An external entity can represent a human, system or subsystem. It is where certain data comes from or goes to. It is external to the system we study, in terms of the business process. For this reason, people use to draw external entities on the edge of a diagram.

Process

 A process is a business activity or function where the manipulation and transformation of data takes place. A process can be decomposed to finer level of details, for representing how data is being processed within the process.

Data Store
A data store represents the storage of persistent data required and/or produced by the process. Here are some examples of data stores: membership forms, database table, etc.

Data Flow

A data flow represents the flow of information, with its direction represented by an arrow head that shows at the end(s) of flow connector.


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