The systems life cycle

By Odaly Fernandez

Stages of the systems life cycle

What is a systems life cycle?

Analysis

Design

Development and testing

Implementation

Documentation

Evaluation

ScenarioThe 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.

Analysis

Collecting information on how the existing system works

Establishing its inputs, outputs and processing

Recording information Identifying problems

Analysis

Why do we need the analysis stage? To identify suitable hardware and software for a

new system To identify user and information requirements

Analysis – Collecting information

Examination of documents Questionnaires Interviews Observation

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

Analysis – Recording information about the current system

Data flow diagram.

Orders SystemContext Diagram

Orderprocessing

system

SuppliersCustomersCustomersCustomers

Orderprocessing

system

Customers

Orderprocessing

system

Customers

Orderprocessing

system

Customers Suppliers

Orderprocessing

system

Customers

orders

invoice invoice

orders

Analysis – Recording information about the current system

Suppliers

Process order

Customers

Issue receipt

Ship goods

Orders

Inventory

orders

rejected orders

Order suppliesShipping details

updated product record

order details

supply orders

receipts

order details

receipts

Analysis – Results

Identifying suitable hardware and software for a new system

Identifying the user and information requirements

Activity

Answer question 1, page 76.

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

Design - Inputs

Designing data collection forms

Design Inputs

A well designed data collection form

Design - Inputs

Screen layouts

Design - Inputs

Screen layouts

Design - Outputs

Designing report layouts

Design - Outputs

Designing screen displays

List of records

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

Design – data/file structures Systems flowchart

Payrolltransaction

file

Validatedtransaction

file

Sortedtransaction

filePayrollmaster

file

Updatedmaster

file

Vaidation

Sort

Process payroll

Managementreports

Payslips

Error reports

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

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…

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…

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.

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.

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}

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”

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.

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.

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

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

Activity

Answer question 2, page 76.

Development and testing Testing strategies.

Produce a test plan using test dataTest Test

dataExpected results

Actual results Comment

Input hours worked

(max. hours worked in a week = 65)

-1 Rejected Error message Abnormal data – the system works as expected

65 Accepted Wages calculated Extreme data – the system works as expected

0 Accepted Wages calculated but result was 0

Extreme data – the system works as expected

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

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.

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.