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Friday, April 11, 2014

SYSTEMS DESIGN

Information Systems Life Cycle can be divided into three broad categories. 



SYSTEMS DESIGN

While systems analysis describes what a system should do to meet information requirements, systems design shows how the system will fulfil this objective. The design of an information system is the overall plan or model for that system. Like the blueprint of a building or house, it consists of all the specifications that give the system its form and structure. Information systems design is an exacting and creative task demanding imagination, sensitivity to detail, and expert skills.  

Systems design has three objectives. First, the systems designer is responsible for considering alternative technology configurations for carrying out and developing the system as described by the analyst. This may involve analyses of the performance of different pieces of hardware and software, security capabilities of systems, network alternatives, and the portability or changeability of systems hardware.

Second, designers are responsible for the management and control of the technical realization of systems. Detailed programming specifications, coding of data, documentation, designers are responsible for the actual procurement of the hardware, consultants, and software needed by the system.

Third, the systems designer details the system specifications that will deliver the functions identified during systems analysis. These specifications should address all of the managerial, organizational, and technological components of the system solution. 

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Logical and Physical Design

The design for an information system can be broken down into logical and physical design specifications. Logical design lays out the components of the system and their relationship to each other, as they would appear to users. It showed what the system solution would do as opposed to how it is actually implemented physically. It describes inputs and outputs, processing functions to be performed, business procedures, data models, and controls. (Controls specify standards for acceptable performance and methods for measuring actual performance in relation to these standards. They are described in detail). 

Physical design is the process of translating the abstract logical model into the specific technical design for the new system. It produces the actual specifications for hardware, software, physical databases, input/output media, manual procedures, and specific controls. Physical design provides the remaining specifications that transform the abstract logical design plan into a functions system of people and machines. 

Design Alternative

Like houses or buildings, information systems may have many possible designs. They may be centralized or distributed, on-line or batch, partially manual, or heavily automated. Each design represents a unique blend of all of the technical and organizational factors that shape an information system. What makes one design superior to others is the ease and efficiency with which it fulfils user requirements within a specific set of technical, organizational, financial, and time constraints. 

Before the design of an information system is finalized, analysts will evaluate various design alternatives. Based on the requirements definition and systems analysis, analysts construct high-level logical design models. They then examine the costs, benefits, strengths, and weaknesses of each alternative. 

Illustrate design alternatives for a corporate cost system, which maintains data on the costs of various products produced by the corporation’s operating units in various locations. The first alternative is a batch system that maximizes the efficiency and economy of computer processing but requires extensive manual preparation of data. 

The batch system requires the following steps: 

1. Operating units prepare cost sheets with product cost data by plant. Sheets are mailed to corporate cost accounting at corporate headquarters.

2. Corporate cost accounting reviews cost sheets and prepares transactions forms, which are entered into the system.

3. The corporate product database is updated twice weekly via batch processing. The database maintains standard product cost data by plant and links local product numbers to corporate product numbers. The update also produces standard cost sheets.

4. Copies of the standard cost sheets are mailed back to the operating units.

There is also a time lag between the preparation of operating unit cost sheets and the point when this information is reflected on the product database. 

The second design alternative is an on-line system featuring more timely information and reduced manual effort, but at greater cost for computer processing, software, and security and recovery procedures required to maintain the integrity of the product database. The steps for the on-line system are as follows: 

1. Operating units enter their own product cost data on-line via local CRT terminals with telecommunications links to the central corporate mainframe.

2. Through extensive on-line editing, the operating unit product data are edited. Errors are corrected and the data immediately update the corporate product database.

3. Up-to-date product cost information is available immediately after update. The system produces hard copy standard cost sheets or allows the operating units to perform on-line inquires about product cost information.

This alternative reduces manual activities and provides up-to-date-minute information both to corporate cost accounting and to the operating units. 

The Role of End Users

Technical specialists cannot direct information systems design alone. It demands a very high level of participation and control by end users. User information requirements drive the entire systems-building effort. Users must have sufficient control over the design process to ensure that the system reflects their business priorities and information needs, not the biases of the technical staff. 

Working on design increases users’ understanding and acceptance of the systems, reducing problems caused by power transfers, inter-group conflict, and unfamiliarity with new system functions and procedures. Insufficient user involvement in the design effort is a major cause of system failure. 

Some MIS researchers have suggested that design should be “user led.” However, other researchers point out that systems development is not an entirely rational process. Users leading design activities have used their position to further private interests and gain power rather than to enhance organizational objectives. Users controlling design can sabotage or seriously impede the systems-building effort. 

The nature and level of user participation in design vary from system to system. There is less need for user involvement in systems with simple or straightforward requirements than in those with requirements that are elaborate, complex, or vaguely defined. Transaction processing or operational control systems have traditionally required less user involvement than strategic planning, information reporting, and decision-support systems. Less structured systems need more user participation to define requirements and may necessitate many versions of design before specification can be finalized. 

Different levels of user involvement in design are reflected in different systems development methods. How user involvement varies with each development approach.

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