1. The systems life cycle
By Odaly Fernandez

2. Stages of the systems life
cycle
 What is a systems life cycle?
Analysis
Design
Evaluation
Development and testing
Documentation
Implementation

3. Scenario
The company called Biashara Street Building Supplies in Nairobi,
Kenya, buys bricks, cement, gravel, sand and roof tiles from big
companies and then sells them in smaller quantities to local house
builders.
The company is run by two directors called Peter and Irene. It employs
two secretaries, three sales people and two truck drivers.
It has a computer, but this is mainly used for creating word-processed
letters and sending emails to customers. Its only other use is to keep
records of the company’s customers on a database.
One secretary, Josephine, deals with the workers’ personal
information and is also in charge of keeping customer details.
The other secretary, Mary, keeps information about the hours worked
by the workers and also processes orders from customers.
Irene is in charge of the paying of the workers.
Peter and Irene feel that they could make better use of their computer
system and need a systems analyst to look at how the computer is
used, and to advise them whether or not their business would improve
if they made increased use of the computer. They have invited Daniel
to perform this role.

4. Analysis
 Collecting information on how the existing
system works
 Establishing its inputs, outputs and
processing
 Recording information
 Identifying problems

5. Analysis
 Why do we need the analysis stage?
 To identify suitable hardware and software for a
new system
 To identify user and information requirements

6. Analysis – Collecting
information
 Examination of documents
 Questionnaires
 Interviews
 Observation

7. Analysis – Establishing the inputs, outputs
and processing in the existing system
 Example 1: payroll system
 Inputs: details of the workers
 Processing: calculation of the payrolls
 Output: payslips
 Example 2: orders system

8. Analysis – Recording information
about the current system
 Data flow diagram.
Orders System
Context Diagram
invoice invoice
Customers Suppliers
Order
processing
orders system
orders

9. Analysis – Recording information
about the current system
orders
Customers Suppliers
supply
Process order orders
rejected
receipts
orders
order details
receipts
Shipping Order supplies
order Orders details
details
Issue receipt
updated product Ship goods
record
Inventory

10. Analysis – Results
 Identifying suitable hardware and software for
a new system
 Identifying the user and information
requirements

11. Activity
 Answer question 1, page 76.

12. Design
 The inputs to the system
 The outputs from the system
 The files and/or databases needed to store
the data
 The processing required to produce the
outputs
 Any validation checks that will be needed
 The data needed to test the system

13. Design - Inputs
 Designing data
collection forms

14. Design
Inputs
A well designed
data collection
form

15. Design - Inputs
 Screen layouts

16. Design - Inputs
 Screen layouts

17. Design - Outputs
 Designing report layouts

18. Design - Outputs
 Designing screen displays
List of records

19. Design – data/file structures
 The files and/or databases needed to store
the data. Example: for the payroll system we
need the master file and the transaction file

20. Design – data/file structures
 Systems flowchart
Payroll
transaction
file
Error reports
Vaidation
Validated
transaction
file
Sort
Sorted
transaction
file
Process payroll Payroll
master
file
Management Updated
Payslips
reports master
file

21. Design – data/file structures
 The master file would have the following
attributes:
 Field names
 Field types
 Field lengths
 Validation rules
 Field descriptions
 Selection of key field

22. Design - Validation
A validation routine checks that input data is
sensible and valid before processing.
However validation rules do not guarantee
that the data typed in is correct.
 Range check. Examples:
 A secondary school student is likely to be aged
between 11 and 16. The range check for the field
age would be >=11 and <=16.
 The maximum marks for AS students is 200. So,
the range check would be…

23. Design - Validation
 Length check. Checks the data is not too
short or too long. Examples:
 Telephone numbers in Spain are 9 digits long. So,
the length check validates that no more and no
less than 9 digits are entered.
 A NIE in Spain has this format X1234567R. The
length check would be…

24. Design - Validation
 Format check. Checks the data is in the right
format. Example:
 The NIE in Spain has this format X1234567R.
The format check would ensure that the first
character is a letter, the next 7 characters are
digits, and the 9th character is a letter.

25. Design - Validation
 Invalid character check. Example:
 I have a password field, and I only want the
following characters to be entered: a to z, A to Z,
0 to 9, and nothing else. So, the characters: ?, >,
*, etc. will be invalid characters and the “invalid
character check” won’t accept them.

26. Design - Validation
 Check digit. Designed to capture human
transcription errors. Example:
 ISBN. 13 digits, the last one is the check digit.
This is an ISBN: abcdefghijklm
m = 10 – {(1a + 3b + 1c + 3d + 1e + … + 3l) mod 10}
 Barcode
This is an barcode: abcdefghijklm
m = 10 – {(3a + 1b + 3c + 1d + 3e + … + 1l) mod 10}

27. Design – Other ways of reducing
errors when inputting data
 Coding data. Examples:
 Instead of typing in the word “Female” in a field
Gender, we could type in “F”.
 Instead of “True” or “False”, type in “T” or “F”

28. Design – Specifying the
required hardware
 If there is a heavy volume of data then the
systems analyst would recommend a laser
printer, and not an inkjet printer.
 If the systems analyst determines that the
articles should be bar-coded, then it is
appropriate to use a bar code reader.

29. Design – Specifying the
required software
 Off-the-shelf software. Which is already
written and available.
 Purpose-built software. Which has to be
specially written to solve the problem.

30. Design – Specifying the
required software
 Off-the-shelf software
 Advantages:
 Cheaper as it is mass produced
 Available straight away
 Testing rigorously carried out by the developers
 Helplines with operators who have had to deal with a wide
range of problems
 Disadvantages:
 May be difficult to adapt to the particular use
 May have several distracting extra features unsuitable for
the use
 May not necessarily match up with the existing system and
software use

31. Design – Specifying the
required software
 Purpose-built software
 Advantages:
 Designed specifically for the task
 Does not have to be adapted for use
 Programmers can make any changes required
 Disadvantages:
 Costs more to pay programmers to write code specifically
for the task
 Testing limited to the perception of use by the programmer
 Support limited to the team of programmers
 Can take a long time to develop

32. Activity
 Answer question 2, page 76.

33. Development and testing
 Testing strategies.
 Produce a test plan using test data
Test Test Expected Actual results Comment
data results
Input -1 Rejected Error message Abnormal data – the system
hours works as expected
worked
65 Accepted Wages calculated Extreme data – the system
(max.
works as expected
hours
worked 0 Accepted Wages calculated Extreme data – the system
in a but result was 0 works as expected
week =
65) 40 Accepted Wages calculated Normal data – the system
works as expected
140 Rejected Error message Abnormal data – the system
works as expected
Abc Rejected Error message Abnormal data – the system
works as expected

34. Development and testing
 Using live data.
 Compare the results of the new system with the
results of the old system. Example: use the hours
worked in past weeks, and compare the payslips
with the ones the new system generates.

35. Development and testing
 Activity:
 Create a table called Student with the fields:
idstudent, name, marks
 Produce a test plan for the marks of the students,
taking into account that the minimum mark is 0
and the maximum is 200.
 Produce a test plan for idstudent, where idstudent
has 8 characters, the first and last character
should be a letter, the rest of the characters are
digits from 0 to 9.