System life cycle is an organizational process of developing and maintaining systems. It helps in establishing a system project plan, because it gives overall list to processes and sub processes required developing a system.
System development life cycle means combination of various activities. In other words we can say that various activities put together are referred as system development in life cycle. In the system analysis and design terminology, the system development life cycle mean software development life cycle.
The following are the different phase of software development cycle:
- System study
- Feasibility study
- System analysis
- System design
- Coding
- Testing
- Implementation
- Maintenance
1. System Study
System study is the first stage of system development life cycle. This gives a clear picture of what actually the physical system is? In practice, the system study is done in two phases. In first phase, the preliminary survey of the system is done which helps in identifying the scope of the system. The second phase of the system study is more detailed and in-depth study in which identification of user’s requirement and limitation of problems of the present system are studied. After completing the system study, a system proposal is prepared by the system analyst (who studied the system) and placed before the user. The proposal system contains findings of the present system and recommendations to overcome the limitations and problems of the present system in the light of users requirements.
To describe the system study phase more analytically, we would say that system study phase passes through the following steps:
- Problem identification and project initiation.
- Background analysis
- Inference or findings
2. Feasibility Study
On the basic of result of the initial study, feasibility study takes place. The feasibility study is basically the test of the proposed system in the light of its workability, meeting user’s requirement, effective use of resources and of course, the cost effectiveness. The main goal of feasibility study is not to solve the problem but to achieve the scope. In the process of feasibility study, the cost and benefits are estimated with greater accuracy.
3. System Analysis
Assuming that a new system is to be developed, the next phase is system analysis.. Analysis involved a detailed study of the current system, leading to specifications of a new system. Analysis is a detailed study of various operations performed by a system of their relationships within and outside the system. During analysis, data are collated on the available files, decision points and transactions handled by the present system. Interviews, on-site observation and questionnaire are the tools used for system analysis. Using the following steps it becomes easy to draw the exact boundary of the new system under consideration.
- keeping in view the problems and new requirements
- working the pros and cons including new areas of the system.
All procedures, requirements must be analyzed and documented in the form of detailed data flow diagrams (DFDs) data dictionary, logical data structures and miniature specification.
System Analysis also includes sub-dividing of complex process involving the entire system, identification of data store and manual processes.
The main points to be discussed in system analysis are:
- Specialization of what the new system is to accomplish based on the user requirements.
- Functional hierarchy showing the functions to be performed by the new system and their relationships with each other.
- Function network which are similar to function hierarchy but they highlight those functions which are common to more than one procedure.
- List of attributes of entities – these are the data items which need to be held about each entity (record).
4. System Design
Based on the user requirements and the detailed analysis of a new system, the new system must be designed. This is the phase of system designing. It is the most crucial phase in the development of a system. Normally, the design proceeds in two stages:
- Preliminary or general design
- Structured or detailed design.
Preliminary or Design
In the preliminary or generally design, the features of the new system a specified. The cost of implementing this features and the benefits to be derived are estimated. If the project is still considered to be feasible, remove to the detailed design stage.
Structure or Detailed Design
In the detailed design stage, computer oriented work begins in the earnest. At this stage, the design of the system becomes more structured. Structure design is a blue print of a computer system solution to a given problem having the same components and inter-relationship among the same components as the original problem. Input, output and processing specifications are drawn up in detail. In the design stage, the programming language and the platform in which they new system will run are also decided.
There are several tools and techniques used for designing. These tools and techniques are:
- Flowchart
- Data flow diagram (DFDs)
- Data dictionary
- Structure English
- Decision table
- Decision tree
Each of the above tools are designing will be discussed in the detail shortly.
5. Coding
After designing the new system, the whole system is required to be converted into a computer understanding language. (Coding) the new system into computer programming language does this. It is an important stage where they defined procedures are transformed into control specifications by the help of the computer language. This is also called the programming phase in which the programmer converts the program specifications into computer instructions, which will refer as a programs. The programs coordinates the data movements and control the entire process in a system. It is general felt that the programs must be modular in nature. This herbs in fast development, maintenance and future, if required
6. Testing
Before actually implementing the new system into operations, a test run of the system is done removing all the bugs, if any. It is an important phase of a successful system.
After codifying the whole programs of the system, a test plan should be developed or run on a given set of test data. The output of the test run should match the expected results.
Using the test data, a test data is carried out. We have:
- Unit test
- System test
Unit Test
When the the programs have been coded and complied and brought to working conditions, the most the individual tested with the prepared test data. Any undesirable happen in a month be noted and the debugged (error corrections).
System Test
After carrying at the unit test for each of the programs of the system and which errors are removed. Then system test is done. At this stage the test is done on actual data. The complete system is executed on the actual data. At each stage of execution, the results or output of the system is analyzed. During the results analysis, it may be found that the outputs are not matching the expected outputs of the system. In such case, the errors in the particular programs are identified and fixed and further tested for the expected output.
When it is insured that the system is running error-free, the users are called with their own actual data the system could be shown running as bad per requirements.
7. Implementation
After having the user acceptance of the new system developed, the implementation phase begins. Implementation is the stage of a project during the theory is turned into practice. During this phase, all the programs of the system are loaded onto the user computer. After loading the system, training of the users starts. Main topics of such type of training are:
- How to execute the package
- How to enter the data
- How to process the data (processing details)
- How to take out the reports.
After the users about the computerized system, manual working has to shift from manual to computerized working. The following two strategies are followed for running the system:
1. Parallel Run: In this method of conversion, both the system i.e, computerized a manual are executed in parallel for a given period of time. This strategy is helpful because of the following:
- Manuel results can be compared with the results of the computerized system.
- Failure of the computerized system at the early stage, does not affect the working of the organization, because the manual system continues to work, as it used to do.
2. Pilot Run: In this type of run, the new system is installed in parts. Some parts of the new system is installed first and executed successfully for considerable time period. When the results are found satisfactory then only other parts are implemented. This strategy builds the confidence and the errors are traced easily.
8. Maintenance
Maintenance is necessary to eliminate errors in the system during its working life and to tune the system to variations in its working environment. It has been seen that there are always some errors found in the system that must be noted and corrected. It’s also means that review of the system from time to time. The review of the system is done for:
- Knowing the full capability of the system.
- Knowing the required changes or the additional requirements.
- Studying the performance.
If a major change to a system is needed, a new project may have to be set up to carry out the change. The new project will be proceed through all the above life cycle phase.
So far we have: Learned the systematic approach of any given problem.
Computer based systems are defined. System development life cycle is discussed in detail. The different phases of the development of system life cycle are explained in detail.