RMP Resource - DFD (Data Flow Diagram)

A DFD is a graphical representation of the flow of data through an information system. It can be used to provide a clear representation of any function. It don't provide information about the timing of processes or about whether processes will operate in sequence. Therefore it is different from a flowchart.

To design DFD, following symbols are used:

External Entity

The symbols used is an oval containing a meaningful and unique identifier. It is a source or destination of a data flow. Only those entities which originate or receive data are represented by this symbol.

Process

It is represented by a rectangular box shows a transformation or manipulation of data flows within the system, it contains 3 descriptive elements:

• An identification number appears in the upper left hand corner. This is allocated arbitrarily at the top level and serves as a unique reference.
  
  
• A location appears to the right of the identifier and describes where in the system the process takes place. for example it may be a department or piece of hardware.
  
• A descriptive title is placed in the centre of the box. This should be a simple imperative sentence with a specific verb, for example 'maintain customer record' or 'find driver'.

Data Flow

It is represented by a line with arrowheads showing the direction of flow. It shows the flow of information from its source to its destination. Information always flows to or from a process and may be written, verbal or electronic.

Data Store

It is a holding place for information within the system, it is represented by an open ended narrow rectangle. Data store may be long term files such as sales ledgers or may be short term accumulations.

Example of DFD:

The different versions are Context Diagrams (Level 0), Partitioned Diagrams (single process only -- one level), Functionally decomposed, leveled sets of Data Flow Diagrams.

The main principle for creating DFD is that one system may be disintegrated into subsystems, which in turn can be disintegrated into subsystems at a much lower level, and so on and so forth. Every subsystem in a DFD represents a process. Each process in a DFD characterises an entire system. Here data is introduced into the system from the external environment.