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Unit 7 - Systems Life Cycle (Stage 2 - design (What does it involve?…
Unit 7 - Systems Life Cycle
What is a systems life cycle?
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 2 - design
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
Performed on numbers to check they are within certain ranges
Limit check
Performed on numbers to make sure that data is not above or below a specified limit.
Length check
Checks that the correct number of characters has been entered
Format check
Makes sure that data is in a specific format
Presence chekc
Checks that data has been entered and not missed out
Data type check
Checks that entered data does not contain invalid characters
Consistency check
Makes sure that data in one field is consistent with data in another field.
System verification
Double entry
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.
Visual check
This is where the person entering data into the computer system carefully compares what they have entered with the data in the original document
Stage 3b - Testing
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.
Stage 3a - development
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:
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
On-screen outputs
Printed outputs (hard copies)
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.
Outputs are tested by checking that the information output is clear, easy to read, complete and correct
Stage 4 - Implementation
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.
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
Fairly cheap method of gathering data
Answers are more honest as they can be answered anonymously
Questions can be answered quickly
Disadvantages
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
Questions can be changed depending on who you're interviewing
More complex questions can be asked
Questions can be explained if misunderstood
Disadvantages
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
