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 life cycle. In the System Analysis and Design terminology, the system development life cycle means software development life cycle.
Following are the different phases of software development cycle:
The different phases of software development life cycle is shown in Fig.29.1
Different phases of Software development Life Cycle
PHASES OF SYSTEM DEVELOPMENT LIFE CYCLE
Let us now describe the different phases and the related activities of system development life cycle in detail.
(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. After completing the system study, a system proposal is prepared by the System Analyst (who studies the system) and placed before the user. The proposed system contains the findings of the present system and recommendations to overcome the limitations and problems of the present system in the light of the user’s 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
inference or findings
(b) Feasibility Study
On the basis 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 requirements, 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.
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(c) 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 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 analyzed 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 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:
Data flow diagram (DFDs)
After designing the new system, the whole system is required to be converted into computer understanding language. Coding the new system into computer programming language does this. It is an important stage where the defined procedures are transformed into control specifications by the help of a computer language. This is also called the programming phase in which the programmer converts the program specifications into computer instructions, which we refer as programs. The programs coordinate the data movements and control the entire process in a system.
It is generally felt that the programs must be modular in nature. This helps in fast development, maintenance and future change, if required.
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 analyzed. 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.
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 computerized system, manual working has to shift from manual to computerized 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. computerized and manual are executed in parallel. This strategy is helpful because of the following:
Manual 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.
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.
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.
Life Cycle Models
The spiral model
Rapid application model
Requirements analysis & Definition
Integration and Software testing
Implementation and unit testing
Operation and Maintenance
This takes the fundamentals process activities of specification, development, validation and evolution and represents them as separate process phase such as requirement specification, software design, implementation and testing and so on.
Requirement Analysis and Definition
The system’s services, constraints and goals are established by consultation with the software users. They are then defined in detail and serve as a software specification.
how the current software works and what it does
Producing a detailed model in subject terms of what the new software will do and how it will work.
Producing a high-level description of new software
The software design process partitions the requirements to either hardware or software system. It establishes overall software architecture. Software design involves identifying and describing the fundamental software system abstraction and their relationships.
Implementation and Unit Testing
During this stage, the software design is realized as a set of programs or program units. Unit testing involves verifying that each unit meets its specification.
Integration and Software Testing
The individual program units or programs are integrated and tested as complete software to ensure that the software requirements have been met. After testing, the software system is delivered to the customer.
Operation and Maintenance
Normally this is the longest life cycle phase. The software is installed and put into practical use. Maintenance involves correcting errors which were not discovered in earlier stages of the life cycle; improving the implementation of the software units and enhancing the software’s services as new requirement are discovered.
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