Unit 7 system life cycle
System life cycle in order: Analysis
Design Development and testing implementation documentation Evaluation
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Analysis - During the analysis stage systems analysts investigate the existing system to identify exactly what the problems are with the existing system
Feasibility study-
For any project, the feasibility study will examine how realistic the proposed solution is, to meet the aims of the project. It will also compare and contrast the options put forward to complete the project. It will examine issues such as costs, manpower, timescale and so on.
At the end of a feasibility study, there will be recommendations on the best way forward (or the study may even recommend cancelling the project if it not feasible).
This is a relatively cheap way of checking that the project will succeed before a lot of money and time is spent on it.
Design-
Alternative possible solutions are identified
Alternative solutions evaluated
The best solution is identified
Validation and verification rules are put into place during the design stage
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Range check
Checks that a value falls within the specified range
EG. Number must be between 1-10
Length check
Checks the data isn't too short or too long
A username that is required to only be 10 characters long
Data type check
Checks that the data entered doesn’t have invalid characters
A field where only numbers should be entered like age, should not allow text to be entered
Format check
Checks the data is in the right format
Date has to be in the format of DD/MM/YYYY
Presence check
Checks the data is in the right format
Some fields can not be left blank
Consistency
A check that is performed to make sure that the data has no internal conflict
If male has been entered the title entered can not be 'Mrs.'
Check digit
The last one or two digits in a code are used to check the other digits are correct
Barcodes in the supermarket use check digits
Development and testing
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There are 4 main parts of development
Creating a file structure to store data
Systems that are required to hold data need to use file structure
File structures determine how the data is stored in the system and are made up of 4 parts:
Tables Fields Field Properties Records
Test data is entered into the fields to make sure that data is being data is being stored correctly
Create validation rules to make sure that the data entered is sensible
Validation checks will have been thought about and decided on during the design stage
Once all of the necessary validation checks have been programmed into the system, they are tested to make sure that they work
Create a user interface to allow data to be input into the system
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. Data entry forms should be well designed to make sure that they are easy to use.
A good entry form should include
Entries for all required fields
Make appropriate use of form controls
Include instructions about entering data
Make sure that the text boxes are big enough
Easy to understand
Create output formats
Two types of system outputs have to be created: onscreen and printed
The system developer will create all outputs by following designs provided
The developer will ensure that all hard copies are printable
Outputs are tested to check if they are clear and easy to use
Testing
To test a system you need a testing plan.
EG there is a range for data entered lets say 1-10
Any number between 1-10 would be a NORMAL value
Number 1 and 10 are Extreme values
Numbers outside the range or not written in integer format are ABNORMAL
Implementation
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Direct Changeover
The old system stops getting used one day and the new system is used the next day
The changeover is fast
ADVANTAGES:
Fastest way of changing systems
New system can be used automatically after installation
Cheap as you dont pay for two sets of staff
DISADVANTAGES
Staff have to be fully trained to use the system before its installed
If the new system fails all the data will be lost because the old system is completely removed and there is no back up
Difficult to plan
Parallel running
The old system and the new system will run alongside each other for a period of time
Data would be inputted into both systems producing two sets of results
When staff are certain about the new system the old one is shut off
ADVANTAGES
If the new system fails the old one is still available
Staff can be trained gradually
Good way to test the system using live data
Disadvantages
Expensive due to the price of running two systems at once
Pilot running
Involves introducing the new system to one part of the company and then rolling it out to other departments.
Good way to implement system without having to massively restructure the company
ADVANTAGES
If the system fails it only affects one part of the company
On a smaller scale and is easier to manage
Staff can be trained gradually
Cheaper
DISADVANTAGES
Takes a very long time
The department doing the testing might lose its data if the system fails
Phased implementation
New system is implemented in phases
ADVANTAGES
Staff can be trained gradually
Easier to find system errors
DISADVANTAGES
Expensive
Only suitable for systems that can be split
Takes a long time
Documentation
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Technical documentation is produced for the benefit of future developers of the system. This like a manual which explains how the system was developed and includes information like software and hardware requirements, file structures and coding used.
Why is it important?:
It gives future analysts, programmers and designers the knowledge needed to repair/maintain/improve the system.
Summary:
Technical documentation
Purpose of the system
Hardware requirement
Software requirement
Memory requirement
Copies of all system designs
Copies of system flowcharts
Explanation of file structures used
Programming language used to code the system
Listings of the code
Details of system bugs
User interface designs
Input formats
Output formats
Validation rules used
Meaning of error messages
Testing information
User documentation is produced for the benefit of the intended users of the system.
Why is it important?:
It explains to the users exactly how the system is supposed to be used.
Summary:
User documentation
Purpose of the system
Hardware requirements
Operating system required
How to open/load the system
How to log in and out of the system
How to search for system data
How to input new data
How to amend data
How to sort data
How to save files
How to print files
How to handle system errors
FAQs
Troubleshooting guides
Help guides
Evaluation
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Why is it important to evaluate?
Systems are evaluated to determine if:
The system is doing the job it was designed to do
The system is working well with minimum errors
Staff can use the system properly
GOOD EVALUATION INCLUDES:
Effective?
Does it work fast?
Does run smoothly?
Does it save the company time and money?
Does it reduce paper waste?
Easy to use?
Does it have a user-friendly interface?
Can everyone use it easily?
Can it be used with minimal training?
Appropriate?
Does it perform the job it was designed to do?
Are the clients happy with it?
Is there anything it cant do that it should?
HOW IS AN EVALUATION CARRIED OUT?:
Comparing the system against the initial requirements
Evaluating user's experiences
Identifying limitations of the new system
Identifying system improvements
FINAL IMPROVEMENTS:
Error correction
Add functionality
Performance improvement