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DATA FLOW DIAGRAMS
A Data Flow Diagram is a graphical representation of
flow of data through information system.
DFD can be used to visualize a data processing.
DFD shows what kind of data will be input to the
system and what data is received as the output. Also it
tells where the data will come from and go to and
where it is stored in the process.
DFDs are drawn with the help of Mac Draw.
COMPONENTS OF A DFD
Also known as bubble, function or transformation.
Shows the part of the system that transforms inputs
to the outputs.
Also represents who is actually carrying out the
Represented graphically by an arrow.
Shows the movement of information packets
i.e., data in motion.
A flow carries only one type of packet and is
represented by the flow name.
THE FLOW (CONTD.)
Data flows can diverge or converge in DFDs.
Models a collection of data packets that are at rest.
Acts as a storage area for two processes that occur
at different times or simultaneously.
Flow from the store is interpreted as access to read
the information from the store.
Flow to a store is interpreted as write update or
Represents an external entity with which the
Can be a person, or a group outside
organisation, department within the organisation or
some other computer system .
Source – Entity that supplies data to the system.
Sink – Entity that receives data from the system
A physical data flow diagram is a graphical
representation of a system showing the system’s
internal and external entities, and the flows of data
into and out of these entities.
A physical DFD specifies who is actually carrying
out the process.
A physical DFD does not tell us what is being
It specifies the logical processes performed on the
A logical DFD portrays system’s activities, whereas
a physical DFD depicts a system’s infrastructure.
SYSTEM DESCRIPTION WITH A DFD
An entire system is depicted by a single data flow
diagram which gives the complete system overview.
This is called context diagram.
Successive expansion of processes is done to
show the operations in details. This is levelling of
In the process of levelling the DFD we still do not
specify how the processing is being done, only the
data flow is specified.
GOOD CONVENTIONS IN PREPARING THE
Accurately level the components of the DFD.
Less number of processes.
Number the processes.
Avoid complex DFDs.
Logically consistent DFDs should be prepared.