CHAPTER 6 -:SYSTEM DESIGN

The objective of the system design is to deliver the requirements as specified in the feasibility report. System design involves first logical design (logical design) and then physical construction (detailed design) of the system. The logical design describes the structure and characteristics of features, such as the outputs, inputs, files, databases, and procedures. The physical construction produces actual program software, files, and a working system.

A two part -design process:

The two design documents describe the same system, bit in different ways because of the different audiences for the documents. The conceptual design answers the following questions.

l Where will the data come from?

l What will happen to the data in the system?

l How will the system look to users?

l What choices will be offered to users?

l What is the timing of events?

l How will the reports and screens look like?

The conceptual design describes the system in language understandable to the customer. It does not contain any technical jargons and is independent of implementation.

By contrast, the technical design describes the hardware configuration, the software needs, the communication interfaces, the input and output of the system, the network architecture, and any thing else that translates the requirement into the solution to the customer problem.

Sometimes customers are very sophisticated and they can understand the “what “and “how “together. This can happen when customers are themselves software developers and may not require conceptual design. In such a cases comprehensive design document may be produced.

OBJECTIVES OF DESIGN:

Since the simplification (i.e. the outside view) of a program should be as free as possible aspects imposed by “how” the program will work (i.e. the “inside” view), it is seldom a document from which coding can directly be done.

So design the gap between specifications and coding; taking the specifications, deciding how the program will be organized, and the method it will used, in sufficient detail as to be direct code able.

If the specifications call for a large or complex program (or both) then the design is quite likely to work down through a no of levels. At each level, breaking the implementation problem into a combination of smaller and simpler problems. Filling a large gap will involve a no of steeping stone! The wider the gap, the larger the no of steeping stones. The design needs to be

· Correct and complete

· Understandable

· At the right level

· Maintainable and to facilitate maintenance of the product code software designer do not arrive at a finished designed document immediately but developed a design iteratively through a no of different phases. The design process involves adding details as the designed developed with constant backtracking to correct earlier, less formal, design. The starting point is an informal design which is refined by adding information to make it consistent and make it consistent and complete.