DATA FLOW DIAGRAM
D.F.D. (Data Flow Diagram) is a set of technique and graphical tools that allow the programmer to develop a kind of software specification that is easily understood by the user. It shows a sequence of functional transformations that convert system input to required output. It represents how a data flows through a system and how output is derived from the input through a sequence of function formation. They describe the end-to-end processing in the form of a flow chart from top to bottom.
The Data Flow Diagram shows the use of data in the system pictorially structured analysis making use of some standard conventions. A full description of a system actually consists of a set of DFDs. Different levels of the system can be expressed using different DFD’s.
The notations that are used by out DFD are described in brief below:
1. Rounded Rectangle: It represents functions, which transform input to output. The name inside the rectangle indicates its function.
2. Rectangle: It represents data stores. The name inside the rectangle indicates the type of data stored. A data therefore is a repository of data. A number and a name identify each data stored.
3. Circles: It represents user interaction with the system, which provide input or receive output.
4. Arrows: It shows the direction of data flow. The names describe the type of data flowing along the path.