INPUT/OUTPUT AND FORM DESIGN
The design of an information system produces the details that state how a system will meet the requirements identified during systems analysis.
Design goes through logical and physical stages of development.
Logical Design : It reviews the present physical system, i.e., prepares input and output specifications; makes edit, security, control specifications; details the implementation plan; and prepares a logicil design walkthrough.
Physical Design : It maps out the details of the physical system, plans the system implementation, devises a test and implementation Ian, and specifies any new hardware and software.
Five parts have been included in the system design process.
(1) Output .Design : It determines the system requirements which will normally be converted in terms of output.
- Input Design : Next step is to find what data is to be made available to the system to produce the desired output. The basic documents in which these data are available need to be identified. These documents may have to be revised or new documents may have to be introduced.
- File Design : Once input data is captured in the system, it will be stored in files in a logical manner. The designer will have to devise the techniques of storing and retrieving data from these files.
- Procedure Design : This involves specifications of how processing will be performed e., what functions will be carried out on computer, what will be the different programs and a what sequence the programs will be run.
(v) Control Design : The control design indicates necessary procedure which will ensure correctness of processing, accuracy of data, timely output etc. This will ensure that a system is functioning as per plan.
Design of Software
The principles should guide software design.
- Modularity and Partitioning : Each system should consist of a hierarchy of Lower-level modules are generally smaller in scope and size compared to higher-level modules and serve to partition processes into separate functions.
- Coupling : Coupling refers to the strength of the relationship between modules in a system.
Good designers seek to develop the structure of a system so that one module has little dependence on any other module. Loose coupling minimizes the interdependence between modules. We can achieve this in the following ways :
- Control the number of parameters passed between modules.
- Avoid passing un-necessary data to called modules.
- Pass data only when needed.
- Maintain superior/subordinate relationship between calling and called modules.
- Pass data, not control information.
The objective is to maximize independence between modules by minimizing coupling (reduce module coupling).
- Cohesion : Modules should carry out a single processing function. In cohesive systems, the contents of the. module are so designed that they perform a specific function and are more easily understood by people than system designed by other methods.
The objective is to maximize cohesion, Highly related elements should be in the same module.
- Span of Control : Span of Control refers to the number of subordinate modules controlled by a calling module. In general, we should seek to have no more than five to seven subordinate modules.
Excessive span of control, meaning a high number of subordinate modules, creates considerable overheads in determining which module to invoke under certain conditions and in establishing calling sequences to pass data and receive results:
- Module Size : The number of instructions contained in a module should be limited so that module size is generally small.
In general, we should seek designs in which the modules forces on a single purpose, are highly cohesive, and are loosely coupled.
6.– Shared Modules : Shared use results from the desire to have a certain function, calculation, or type of precessing performed in one place in a system.
Sharing modules minimize the amount of software that must be designed and written. It minimizes the number of changes that must be made during system maintenance.
The designer normally will work under following constraints.
- Hardware : The existing hardware will affect system design.
- Software : The available software (operating system, utilities, Language etc.) in the market will constrain the design.
- Budget : The budget allocated for the project will affect the scope and depth of
Software Design and Documentation Tools
Well designed, modular software is more likely to meet the maintenance, reliability and testing requirement. One of the tool is structured flowchart.
Structural Flowchart : Structured flowcharts, also called Nassi-Schnciderman charts, are graphic tools that force the designer to structure software in modular as well as top-down form. They provide a proper structure that can be retained by the programmer for developing the application software.
The programmer should be expert in using the structured flowcharts.
The basic elements used in developing structured flowcharts are :
Process : Simple processes or steps in a program are shown by a rectangular box, the process symbol. This symbol represents initialisation of values, input and output operations and calls for the execution of other procedures.
Decision : The decision symbol represents alternative conditions that can occur and that the program must have a manner of handling. The decision symbol may show actions for more than two alternatives at the same time.
Interaction : The iteration symbol represents looping and repetition of operations while a certain condition exists or until a condition exists.
The structured flowcharts use no arrows or continuations on separate pages. Each structured flowchart is shown on a single sheet of paper. When designing a structured flowchart, the systems analyst specifies the logic in a top down fashion. The first consideration in a process is the top element. The second in sequence is next one shown and so forth. Similarly, there is a single exit from the process.
Design of Computer Output
The term output applies to any information produced by an information system,
whether printed or displayed. When analysts design computer output, they
Identify the specific output that is needed to meet the information requirements. Select methods for presenting information.
Create document, report or other formats that contain information produced by the system.
The output from an information should accomplish one or more of the following objectives :
1 Convey information about past activities, current status, or projection of the future.
- Tiger an action.
- Signal important events, opportunities, problems or warnings.
- Confirm an action.
Types of Output
Whether the output is a formatted report or a simple listing of the contents of a file, a computer process will produce the output.
System output may be :
- A report
- A document
- A message