14. System Design

The most creative and challenging phase of the life cycle is system design. The term design describes a final system and the process by which it is developed. It refers to the technical specifications that will be applied in implementations of the candidate system. The design may be defined as “the process of applying various techniques and principles for the purpose of defining a device, a process or a system with sufficient details to permit its physical realization”.

The designer’s goal is how the output is to be produced and in what format. Samples of the output and input are also presented. Second input data and database files have to be designed to meet the requirements of the proposed output. The processing phases are handled through the program Construction and Testing. Finally, details related to justification of the system and an estimate of the impact of the candidate system on the user and the organization are documented and evaluated by management as a step toward implementation.

The importance of software design can be stated in a single word “Quality”. Design provides us with representations of software that can be assessed for quality. Design is the only way where we can accurately translate user requirements into a complete software product or system. Without design we risk building an unstable system that might fail if small changes are made. It may as well be difficult to test, or could be one who’s quality can’t be tested. So it is an essential phase in the development of a software product.

Design Methodology

There are basically two types of approaches to develop any system.

• Top down Approach
• Bottom Up Approach

Top down Approach

A top down approach starts by identifying the major components f the system, decomposing them into their lower-level components, and integrating until the desired level of detail id achieved. Top-down design methods often result in some form of stepwise refinement. Starts from an abstract design, in each step the design is refined to a more concrete level, until a level is reach where no more refinement is needed and the design can be implemented directly. The top-down approach has been promulgated by any researchers and has been found to be extremely useful for design. Most design methodologies are based on the top-down approach.

Bottom-Up Approach

A bottom-up approach starts with designing the most basic or primitive components and proceed to higher-level components that use these lower- level components. Bottom-up methods work with layers of abstraction. Starting from the very bottom, operations that provide a layer of abstraction are implemented. The operations of this layer are then used to implement more powerful operations and still higher layer of abstraction, until the stage is reached where the operations supported by the layer are

those desired by the system. Integration is done to obtain above level and this process is continued until overall System is obtained, in this approach the complexity is lying in the integration of different module.