Data flow
diagram is graphical representation of flow of data in an information system.
It is capable of depicting incoming data flow, outgoing data flow and stored
data. The DFD does not mention anything about how data flows through the system.
There
is a prominent difference between DFD and Flowchart. The flowchart depicts flow
of control in program modules. DFDs depict flow of data in the system at
various levels. DFD does not contain any control or branch elements.
Data
Flow Diagrams are either Logical or Physical.
● Logical
DFD - This type of DFD concentrates on the system
process, and flow of data in the system.Forexample
in a Banking software system, how data is moved between different entities.
● Physical
DFD - This type of DFD shows how the data flow is
actually implemented in the system. It is more specific and close to the
implementation.
DFD
can represent Source, destination, storage and flow of data using the following
set of components -
● Entities - Entities
are source and destination of information data. Entities are represented by a
rectangles with their respective names.
● Process - Activities
and action taken on the data are represented by Circle or Round-edged
rectangles.
● Data
Storage - There are two variants of data storage - it can either be
represented as a rectangle with absence of both smaller sides or as an
open-sided rectangle with only one side missing.
● Data Flow - Movement
of data is shown by pointed arrows. Data movement is shown from the base of
arrow as its source towards head of the arrow as destination.
● Level 0 - Highest
abstraction level DFD is known as Level 0 DFD, which depicts the entire
information system as one diagram concealing all the underlying details. Level
0 DFDs are also known as context level DFDs.
● Level 1 - The
Level 0 DFD is broken down into more specific, Level 1 DFD. Level 1 DFD depicts
basic modules in the system and flow of data among various modules. Level 1 DFD
also mentions basic processes and sources of information.
● Level 2 - At
this level, DFD shows how data flows inside the modules mentioned in Level 1.
● Higher
level DFDs can be transformed into more specific lower level DFDs with deeper
level of understanding unless the desired level of specification is achieved.