Experiment-II: Data Flow Diagrams
1. Problem Statement: To design dataflow diagram for software requirements
SOFTWARE REQUIREMENTS: Ms Word.
Data flow diagram (DFD)
A picture is worth a thousand words. A Data Flow Diagram (DFD) is traditional visual
representation of the information flows within a system. A neat and clear DFD can depict a good
amount of the system requirements graphically. It can be manual, automated, or combination of
both.
It shows how information enters and leaves the system, what changes the information and where
information is stored. The purpose of a DFD is to show the scope and boundaries of a system as
a whole. It may be used as a communications tool between a systems analyst and any person who
plays a part in the system that acts as the starting point for redesigning a system.
It is usually beginning with a context diagram as the level 0 of DFD diagram, a simple
representation of the whole system. To elaborate further from that, we drill down to a level 1
diagram with lower level functions decomposed from the major functions of the system. This
could continue to evolve to become a level 2 diagram when further analysis is required.
Progression to level 3, 4 and so on is possible but anything beyond level 3 is not very common.
Please bear in mind that the level of details for decomposing particular function really depending
on the complexity that function.
Diagram Notations
Now we'd like to briefly introduce to you a few diagram notations which you'll see in the tutorial
below.
External Entity
An external entity can represent a human, system or subsystem. It is where certain data comes
from or goes to. It is external to the system we study, in terms of the business process. For this
reason, people used to draw external entities on the edge of a diagram.
Process
A process is a business activity or function where the manipulation and transformation of data
takes place. A process can be decomposed to finer level of details, for representing how data is
