2. Definition
“graphical tool that depicts the sequence of processes
and functions contained within a specified system
boundary and the flow of data through that system”
(Marakas, 2006, p. 117)
Data flow diagrams – shows the flow of data through a
system.
DFDs are logical models because they show what is
done rather than how it is done (physical model).
3. Logical Model: peeling an apple
Get the apple
Get the peeling device
Wash the apple
Hold the apple
Peel the apple with the peeling device
Discard the peel
Process the apple into desired form
4. Physical Model: peeling an apple
Get the apple by removing it from the fruit drawer in the
refrigerator using either hand
Get the paring knife from the upper left-hand kitchen drawer
using either hand after setting the apple down
Wash the apple under the kitchen tap using a scrubbing action
with your hands
Hold the apple in your left hand (use opposite hand if you are
left-handed)
Peel the apple with the knife, with the blade pointing towards
you
Discard the peel in suitable rubbish bin
Eat the apple by biting down on a portion of the apple with your
teeth and chewing
Source (Marakas, 2006, pp. 116-117)
5. DFD: Apple Peeling
S2 Peeling
S1 Apple S3 Peel
Device
Store Disposal
Storage
Unwashed Apple Peeling Device Apple Peel
2.0
1.0 6.0
Get Peeling Peeling Device
Get Apple Discard Peel
Device
5.0
Apple Peel
Peel Apple Processed
Unwashed Apple Peeled Apple
with Peeling Apple System
Device
7.0
3.0 4.0 Send Peeled
Washed Apple Washed Apple Peeled Apple
Wash Apple Hold Apple Apple to
Processor
Source: Marakas, G. M. (2006). System Analysis and Design an active approach. New York: McGraw-Hill/Irwin.
(pg120)