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.