Although this is top down, there is a need for loop back each stage to minimize the errors that would carry forward.

Different phases of Software development Life Cycle

(a) 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 the 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 the identification of user’s requirement and the limitations and problems of the present system are studied.

A system proposal is prepared by the System Analyst. The proposed system contains the findings of the present system and recommendations to overcome the limitations and problems of the present system

problem identification and project initiation
background analysis
inference or findings

(b) Feasibility Study

On the basis of initial study, feasibility study takes place. The feasibility study is basically the test of the proposed system workability, meeting user’s requirements, effective use of resources and .of course, the cost effectiveness.

(c) System Analysis

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 and their relationships within and outside the system.

During analysis, data are collected 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
Workout the pros and cons including new areas of the system
All procedures, requirements must be analysed and documented in the form of detailed data flow diagrams (DFDs), data dictionary, logical data structures and miniature specifications. 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:

Specification 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 relationship with each other.

Function network which are similar to function hierarchy but they highlight the those functions which are common to more than one procedure.

List of attributes of the entities - these are the data items which need to be held about each entity (record)

(d) 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 a most crucial phase in the development of a system. Normally, the design proceeds in two stages :

preliminary or general design
Structure or detailed design

Preliminary or general design:
In the preliminary or general design, the features of the new system are specified. The costs of implementing these features and the benefits to be derived are estimated. If the project is still considered to be feasible, we move to the detailed design stage.

Structure or Detailed design:

In the detailed design stage, computer oriented work begins in 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 the 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
Pesudocode
Decision table
Decision tree

(e) programming phase
After designing the new system, the whole system is required to be converted into computer understanding language. In this stage defined procedure are transformed into control specifications by the help of a computer language.

It is generally felt that the programs must be modular in nature. This helps in fast development, maintenance and future change, if required.

(f) 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 and run on a given set of test data. The output of the test run should match the expected results.

Using the test data following test run are carried out:

Unit test:
When the programs have been coded and compiled and brought to working conditions, they must be individually tested with the prepared test data. Any undesirable happening must be noted and debugged (error corrections).

System Test:
After carrying out the unit test for each of the programs of the system and when 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 the execution, the results or output of the system is analysed. During the result analysis, it may be found that the outputs are not matching the expected out of the system. In such case, the errors in the particular programs are identified and are fixed and further tested for the expected output.

When it is ensured that the system is running error-free, the users are called with their own actual data so that the system could be shown running as per their requirements.

(g) Implementation

After having the user acceptance of the new system developed, the implementation phase begins. Implementation is the stage of a project during which theory is turned into practice. During this phase, all the programs of the system are loaded onto the user's 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 are trained about the computerised system, manual working has to shift from manual to computerised working. The following two strategies are followed for running the system:

Parallel run: In such run for a certain defined period, both the systems i.e. computerised and manual are executed in parallel. This strategy is helpful because of the following:

Manual results can be compared with the results of the computerised system.
Failure of the computerised system at the early stage, does not affect the working of the organisation, because the manual system continues to work, as it used to do.

Pilot run: In this type of run, the new system is installed in parts. Some part 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.

(h) Maintenance

Maintenance is necessary to eliminate errors in the system during its working life and to tune the system to any 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 also means the review of the system from time to time. The review of the system is done for:

knowing the full capabilities 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 then proceed through all the above life cycle phases.


Questions

Define a system. Explain the components of a system.

What do you understand by system development life cycle?

Discuss the importance of system analysis and design in the development of a system?