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:
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.
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'.
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.
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.