Note for System Analysis and Design - SAD By Vandana Verma
- System Analysis and Design - SAD
- Note
- Master of Computer Applications
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Fundamenal of System System is a word derived from the Greek word ‘Systema’ which means an organized relationship among components. A System may be defined as orderly grouping of interdependent components linked together according to a plan to achieve a specific goal. Each component is a part of total system and it has to do its own share of work for the system to achieve the desired goal. An Information system is an arrangement of people, data, processes, information presentation and information technology that interacts to support and improve day-to-day operations in a business as well as support the problem solving and decision making needs of management and users. Characteristics of System:The characteristics of a System are as follows: • Organization implies structure and order. It is an arrangement of components that helps to achieve objectives. • Interaction refers to the procedure in which each component functions with other components of the system. • Interdependence means that one component of the system depends on another component. • Integration is concerned with how a system is tied together. It is more than sharing a physical part. It means that parts of system work together within the system even though each part performs a unique function. • Central Objective is quite common that an organization may set one objective and operate to achieve another. The important point is that the users must be aware about the central objective well in advance. Important Terms Related to Systems Purpose, Boundary, Environment, Inputs, and Outputs are some important terms related to Systems. They are:• A System’s purpose is the reason for its existence and the reference point for measuring its success. • A System’s boundary defines what is inside the system and what is outside. • A System Environment is everything pertinent to the System that is outside of its boundaries. • A System’s Inputs are the physical objects and information that cross the boundary to enter it from its environment. • A system’s Outputs are the physical objects and information that go from the system into its environment. Classification of Systems Systems may be classified as follows: a) Formal or Informal b) Physical or Abstract c) Open or Closed d) Manual or Automated. a) A Formal System is one that is planned in advance and is used according to schedule. In this system policies and procedures are documented well in advance. A real life example is to conduct a scheduled meeting at the end of every month in which agenda of the meeting has already been defined well in advance. An Informal System is the system that is not described by procedures. It is not used. According to a schedule. It works on as need basis. For example, Sales order processing system through telephone calls.
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b) Physical Systems are tangible entities that may be static or dynamic. Computer Systems, Vehicles, Buildings etc. are examples of physical systems. Abstract systems are conceptual entities. Example: Company c) Open System is a system within its environment. It receives input from environment and provides output to environment. Example: Any real life system, Information System, Organization etc. Closed System: It is isolated from environment influences. It operates on factors within the System itself. It is also defined as a System that includes a feedback loop, a control element and feedback performance standard. d) Manual and Automated systems: The system, which does not require human intervention is called Automated system. In this system, the whole process is automatic. Example: Traffic control system for metropolitan cities. The system, which requires human intervention, is called a Manual System. Example: Face to face information centre at places like Railway stations etc. Real Life Business Subsystems A Subsystem is a component of a System, even though it can also be considered as a system in its own right. Consider a manufacturing firm. It consists of five subsystems namely, Product design, Production, Sales, Delivery and Service. . The boundary is between the firm and its environment. In this system, all the subsystems work together to achieve a goal. REAL TIME SYSTEMS A real time system describes an interactive processing system with severe time limitations. A real time system is used when there are rigid time requirements on the flow of data. A real time System is considered to function correctly only if it returns the correct result within imposed time constraints. There are two types of Real Time systems. They are : • Hard Real Time Systems which guarantee that critical tasks are completed on time. • Soft Real Time Systems which are less restrictive type of real time systems where a critical real time task gets priority over other tasks, and retains the priority until it completes them. Systems that control scientific experiments, medical imaging systems, industrial control systems and some display systems are real time systems. Distributed System A Distributed System in which the Data, Process, and Interface component of information System are distributed to multiple locations in a computer network. Accordingly, the processing workload required to support these components is also distributed across multiple computers on the network. In this system, each processor has its own local memory. The processors communicate with one another through various communication lines, such as high buses or telephone lines. The processors in a distributed system may vary in size and function. They may include small microprocessors, workstations, minicomputers, and large general-purpose computer systems. The implementation of a distributed system is complicated and difficult, but still is in demand. Some of the reasons are that modern businesses are already distributed. So, they need distributed solutions. In general, solutions developed using a distributed systems paradigm are user-friendlier. They have the following advantages: • Resource sharing
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• Computation speedup • Reliability • Communication. The five Layers of Distributed System architecture are: • Presentation Layer is the actual user interface. The inputs are received by this layer and the outputs are presented by this layer. • Presentation Logic layer includes processing required to establish user interface. Example: Editing input data, formatting output data. • Application Logic Layer includes all the logic and processing required to support the actual business application and rules Example: Calculations. • Data Manipulation Layer includes all the command and logic required to store and retrieve data to and from the database. • Data Layer is actual stored data in the database. DEVELOPMENT OF A SUCCESSFUL SYSTEM The success of any system depends on the approach of building it. If the development approach is right, the system will work successfully. System development life cycle (SDLC) is a standard methodology for the development of Information System. It mainly consists of four phases: System Analysis, System Design, System Construction & Implementation and System Support. Every phase consist of inputs, tasks and outputs. Traditional SDLC was strictly sequential. The developers first complete the previous phase then start the next phase. But now concept of Repository is introduced in SDLC and it is known as FAST methodology where work is done across shared repository. It means that all the inputs and outputs of phases must be stored in the repository. At any time developers can backtrack to previous phase and they can also work on two phases simultaneously. Preliminary Investigation Determination of system requirement Design of system Development of software System testing Implementation & evaluation For making a successful system, the following principles should be followed: (1) Both customers and developers should be involved for accuracy in the information. (2) A problem solving approach should be adopted. The classic problem solving approach is as follows: a) Study, understand the problem and its context b) Define the requirements of a solution c) Identify candidate solutions and select the best solution d) Design and implement the solution e) Observe and evaluate the solution’s impact and refine the solution accordingly. (3) Phases and activities should be established.
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(4) For consistent development of a system, some standards should be established. These standards are: Documentation standards: It should be an ongoing activity during the system development life cycle. Quality Standards: Checks should be established at every phase for ensuring that the output of every phase meets the business and technology expectations. Automated Tool standards: Hardware and software platforms should be finalized for the development of Information system. Automated tool standards prescribe technology that will be used to develop and maintain information systems and to ensure consistency, completeness, and quality. (5) Development of information system should be considered as capital investment: The developer of an information system should think about several solutions of a particular problem and every solution should be evaluated for cost-effectiveness and risk management. Cost-effectiveness is defined as the result obtained by striking a balance between the cost of developing and operating an information system and the benefits derived from that system. Risk management is defined as the process of identifying, evaluating and controlling what might go wrong in a project before it becomes a threat to the successful completion of the project or implementation of the information system. Multiple feasibility checkpoints should be built into system development methodology. At each feasibility checkpoint, all costs are considered sunk (i.e. not recoverable). Thus, the project should be reevaluated at each checkpoint to determine if it remains feasible to continue investing time, effort, and resources. At each checkpoint, the developers should consider the following options: • Cancel the project if it is no longer feasible. • Re-evaluates and adjusts the cost and schedule if project scope is to be increased. • Reduce the scope if the project budget and schedule are frozen and not sufficient to cover all the project objectives. (6) Divide and Conquer approach is the way of making a complex problem easier. In this approach, the larger problem (System) is divided into smaller problems (Subsystem). (7) For development of a successful system, the system should be designed for growth and change. When the System is implemented, it enters the operations and support stage of Life Cycle. During this stage, the developers encounter the need for changes that range from correcting simple mistakes to redesigning the system to accommodate changing technology to making modifications to support changing user requirements. These changes direct the developers to rework formerly completed phases of the life cycle. Various approaches for development of Information Systems Various approaches are available for development of Information Systems. They are:• Model Driven: It emphasizes the drawing of pictorial system models to document and validate both existing and/or proposed systems. Ultimately, the system model becomes the blueprint for designing and constructing an improved system. • Accelerated approach: A prototyping approach emphasizes the construction of model of a system. Designing and building a scaled-down but functional version of the desired system is known as Prototyping. A prototype is a working system that is developed to test ideas and assumptions about the new system. It consists of working software that accepts input, perform calculations, produces printed or display information or perform other meaningful activities. • Joint Application Development:
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