April 1999
SD206: SYSTEMS DESIGN

QUESTION 3

Total Marks: 20 Marks

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GRADE A
Sample student's solutions are indicated in green.
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(a) (i) Describe two hidden costs which can be reduced by using electronic forms. [4]
(ii) List two drawbacks of using electronic forms. [2]
(i) Two hidden costs:
  1. Cost of running out
    As paper will run out and this causes operation being halted using electronic form, it will never run out because supply always equal demand.
  2. Cost of data float
    Data float is a function of time. It is caused by paper float, the time it takes paper from one point to another point. As electronic form does not require paper, data carried electronically; cost of data float thus reduced.

(ii) Two drawbacks:

  1. Legal constraints.
    Using electronic forms, the evidence document can be easily manipulate to forfeited. Unlike today, paper form is prepared for evidence document.
  2. It is less portable compared to paper form. You must have at least sub-notebook or PC in order to use electronic form and it is considered bulky to be carried around.

 
(b) Describe, using examples, each of the following types of code.
(i) Significant-digit subset codes. [2]
(ii) Cipher codes. [2]
(iii) Sequence codes. [2]
(i) Significant - digit subset codes
The code is divided into subset of code.
For example:

Item number
1 2 3 4 5 6 7 8 9
Product class Vendor number

(ii) Cipher codes
The code is used to cover up information that is not wished to be seen by unauthorised person.
For example:

B L E A C H M I N D
1 2 3 4 5 6 7 8 9 0

for markdown price. Markdown price would be displayed as BIMC on the price tag to prevent customer from knowing it. It would only be known by the staff only. BIMC means $18.75 for markdown price.

(iii) Sequence code
It uses numeric or letter in serial to show the order in which event occurred. Usually used for identification.
For example:

Student index number
0001
0002

 
(c) Give one example of how each of the following guidelines can aid coding. [1]
(i) "Avoid confusing codes". [1]
(ii) "Keep codes concise". [1]
(iii) "Keep codes stable".
(i) Avoid confusing codes (avoid codes that similar)
Eg: 5 and the letter 'S'. This should be avoided.

(ii) Keep codes concise (avoid long code, as for inevitable long codes such as phone number, it should be divided into subcode)
Eg: 001-65-2581675

(iii) Keep code stable (semantic remains unchanged)
Eg: ppi which sometimes could mean point-per-inch and the other time it's picas-per-inch. This should be avoided.

 
(d) Give one example of each of the following means of validating input data.
(i) Test for reasonableness. [1]
(ii) Test for invalid values. [1]
(iii) Test for comparison with stored data. [1]
(i) Test for reasonableness
Eg: age of a person should be reasonable one. It should not be 1200 or 120 years old.

(ii) Test for invalid values
Eg: there exists only two values allowed such as

  1. Add
  2. Delete
  3. Print out

You should not enter value other than 1, 2, 3.

(iii) Test for comparison with stored data
Eg: the item number entered should be the one that exists in the stored data and correct one.

Entered data ® 11AB
Stored data ® 12AB
14AB

 
(e) When is the check digit approach useful? [2]
  • When the code used is 5 or 6 digit.
  • When the numeric code used has no meaning.
  • When the transposition error and miskey error often occur.