The systems life cycle
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The systems life cycle By Odaly Fernandez
description
Transcript of The systems life cycle
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.
