The document defines data flow diagrams and provides examples of logical and physical models for peeling an apple. A DFD shows the flow of data through a system and is a logical model that depicts the sequence and functions without detailing how they are performed. The document then provides a DFD for peeling an apple with 7 steps and 3 data stores that shows the flow of an unwashed apple through getting, washing, peeling, and processing the apple.

1. Week 4
Data Flow Diagrams (DFD) Part 1

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)