System Analysis and Design
INTRODUCTIONSystems are created to solve problems. One can think of the systems approach as an organized way of dealing with a problem. In this dynamic world, The subject System Analysis and Design, mainly deals with the software development activities.
OBJECTIVES
After going through this lesson, you should be able to:
- understand a system
- understand the different phases of system developments life cycle
- know the components of system analysis
- know the components of system designing
A collection of components that work together to realize some objective forms a system. Basically there are three major components in every system, namely input, processing and output.
SYSTEM LIFE CYCLE
System life cycle is an organisational process of developing and maintaining systems. It helps in establishing a system project plan, because it gives overall list of 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 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:
- System study
- Feasibility study
- System analysis
- System design
- Coding
- Testing
- Implementation
- Maintenance
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
- background analysis
- inference or findings
(b) 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 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)
(c) 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
- Structured English
- Decision table
- Decision tree
Each of the above tools for designing will be discussed in detailed in the next lesson.
(d) 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.
PHASES OF SYSTEM DEVELOPMENT LIFE CYCLELet us now describe the different phases and the related activities of system development life cycle in detail.
What You Have Learnt
In this lesson systematic approach of any given problem is explained. 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.
Terminal Question
- 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?
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