Unit 7 - Systems Life Cycle

What is a systems life cycle?

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Stage 2 - design

Stage 3b - Testing

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Stage 3a - development

Stage 4 - Implementation

This is the process of looking at an existing system and then designing a new system that can carry out the same tasks better.

If a system is developed without proper planning or design, serious faults are usually found in the system later on when it has been built

Any faults discovered once the system has been built are very expensive and time-consuming to correct.

By carrying out proper planning before starting to build the system, these potential faults are minimised.

Stage 1 - Analysis

This is where the current system is looked at in detail in order to figure out what changes need to be made to make new system better than the old one

What does it involve?

Collecting data about the current system

Find out problems with the current system

Establish the problem that the customer needs solving

Identify inputs, processing and outputs of the current system

Identify the requirements of the new system

Producing a cost-benefit analysis

Methods to obtain information for analysis

Questionnaires - prepared questions to the users of the system and they are left with the user to complete.

Advantages

Disadvantages

Fairly cheap method of gathering data

Answers are more honest as they can be answered anonymously

Questions can be answered quickly

Difficult to ask specific questions

Unclear questions cannot be explained as people are left alone to answer questionnaires

Questionnaires are often not complete or people do not complete the questionnaire

Interviews - can take place face-to-face, usually involve more detailed questions.

Advantages

Disadvantages

Questions can be changed depending on who you're interviewing

More time consuming than questionnaires

Answers may not be as honest as the person being interviewed can't be remained anonymous

Observations -where system analyst sits and watcher somebody using the current system

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Once there is a clear list of requirements for the new system it is time to design how it will look and work.

What does it involve?

Designing printed outputs (reports, customer bills etc.)

Designing screen-based outputs

Designing user-interface layouts

Designing structures to store data

Designing data entry screens

Designing data validation methods

Designing verification methods

Data validation methods

Designing system validation - where computer system checks that data entered by the user is sensible and usable

Range check

Limit check

Length check

Format check

Presence chekc

Data type check

Consistency check

Checks that data has been entered and not missed out

Checks that the correct number of characters has been entered

Performed on numbers to check they are within certain ranges

Performed on numbers to make sure that data is not above or below a specified limit.

Makes sure that data is in a specific format

Checks that entered data does not contain invalid characters

Makes sure that data in one field is consistent with data in another field.

System verification

Double entry

Visual check

This is where data is entered twice by two different people. The computer compares the two entries and lets the user know if it finds any differences.

This is where the person entering data into the computer system carefully compares what they have entered with the data in the original document

This part just means to 'build the system'

Stages of development

Creating file structures to store data

Systems that are required to hold data need to use file structures

File structures determine how the data is stored in the system and are made of 4 parts: tables, fields, field properties, records.

Example: ict shit

Creating validation rules

Validation checks are tested in two ways

Entering data that should be accepted

Purposefully entering data that should not be accepted

Validation checks will have been thought about and decided on during design stage. Once they have been programmed, they are tested.

Creating input methods

User interfaces have to be created to allow users to input data into the system

The screens of a system that allow users to enter data into the system are called 'data entry forms' they should be well designed to make sure that they are easy to use.

Creating output formats

Two types of system outputs

The developer will ensure that any hard copy outputs will be printable by clicking a 'print button

The system developer will create all outputs by following designs provided during stage 2.

On-screen outputs

Printed outputs (hard copies)

Outputs are tested by checking that the information output is clear, easy to read, complete and correct

When each module (part) of the system has been created it must be tested to make sure that it works correctly

Testing with normal, extreme and abnormal data

Normal data - Data which should be accepted and pass the test without any problems

Extreme data - Data which is on the border of what the system will accept.

Abnormal data - Data should not be accepted by the system.

Live data - (is used to test the system after it has been installed into the customer's workplace) Data that is actually used in the customer's company

Once all the individual parts have been tested and all the problems were solved, the system is then tested as a whole, AKA integration testing.

Testing the system as a whole can ensure that all the individual parts of the system are working correctly with each other.

Any more problems that are found will be corrected and then the system is re-tested.

Implementation just means to 'install' the system ready for use

Methods of implementation

Parallel running - The old and new system are run alongside each other for a period of time. When staff has gotten used to the new system or understood it better, then the old system is shut down and the new system will be used exclusively.

Pilot running - This is where the new system is introduced to one part of the company first and then gradually more staff from diff departments will learn about it too..

Phased implementation - Type of change over where the new system is implemented one part at a time, in phases.

Direct Changeover - With direct changeover, the old system stops getting used one day and the new system getting used the next.