December 1999
SD206 : SYSTEMS DESIGN

QUESTION 2

Total Marks: 15 Marks

• Question 1
• Question 3
• Question 4
• Question 5
• Cover Page

SUGGESTED SOLUTIONS
Solutions and allocated marks are indicated in green.
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Illustrate,using a simple example,how a system can be modelled using a data flow diagram .
One mark should be awarded for using each symbol correctly,i.e.,entities,data .ows, processes,and data stores,and a further mark should be awarded for a sensible example which uses the symbols correctly.

Describe,using examples,the first two steps involved in deriving a logical model of a new system from a logical model of an existing system.
For each of the following,one mark should be awarded for correctly naming the stage, one mark should be awarded for a satisfactory explanation,and a further mark should be awarded for a suitable example.

•Resequence (1 mark).This stage involves taking an existing data flow diagram and resequencing the activities to incorporate parallelism,etc. (1 mark).Any suitable example which illustrates this activity (1 mark).

•Reduce data redundancy (1 mark).This stage involves reducing replication ofdata in order to reduce data redundancy and increase data integrity (1 mark).Any suitable example which illustrates this activity (1 mark)

The first four steps necessary for developing a structure chart are:perform a transaction analysis,determine the central transform,produce a first-cut structure chart,and add modules and show data flows.Describe the final two steps involved in developing a structure chart.
For each of the following,one mark should be awarded for naming the step,and a further mark should be awarded for a satisfactory elaboration.

•Write module details (1 mark).The structure chart depicts the overall design ofthe program;details ofthe modules are specified using an algorithmic language,such as pseudocode or Structured English (1 mark).

•Conduct software design walkthrough (1 mark).After the modules have been specified,a structured walkthrough should be conducted to review that the structure chart has been designed in accordance with the new system requirements (1 mark).