Process ModellingWeek 4

Data Flow Diagrams (DFD) Part 1

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).

Logical Model: peeling an appleGet the appleGet the peeling deviceWash the appleHold the applePeel the apple with the peeling deviceDiscard the peelProcess the apple into desired form

Physical Model: peeling an appleGet the apple by removing it from the fruit drawer in the

refrigerator using either handGet the paring knife from the upper left-hand kitchen drawer

using either hand after setting the apple downWash the apple under the kitchen tap using a scrubbing

action with your handsHold 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

youDiscard the peel in suitable rubbish binEat the apple by biting down on a portion of the apple with

your teeth and chewingSource (Marakas, 2006, pp. 116-117)

DFD: Apple PeelingS1 Apple

Store

S2 Peeling Device Storage

S3 Peel Disposal

1.0Get Apple

2.0Get Peeling

Device

3.0Wash Apple

4.0Hold Apple

5.0Peel Apple

with Peeling Device

6.0Discard Peel

7.0Send Peeled

Apple to Processor

Processed Apple System

Unwashed Apple

Unwashed Apple

Peeling Device

Washed Apple

Peeling Device

Washed Apple

Peeled Apple

Apple Peel

Apple Peel

Peeled Apple

Source: Marakas, G. M. (2006). System Analysis and Design an active approach. New York: McGraw-Hill/Irwin. (pg120)