A Systems Design Life Cycle
A computer-based information system has a life cycle just as
a living organism or a new product does.
The various stages in the systems life cycle are show in the Table
below. The idea for a new information
system is stimulated by a need to improve existing procedures or take advantage
of a new opportunity. This need leads to
a preliminary survey to determine if a system can be developed to meet the
objectives of the individuals suggesting it. If the results of the survey are
positive, it is refined to produce a more detailed feasibility study. From the outcome of the feasibility study, a
decision is made whether to proceed with the design of a system. If a positive decision is made, one of the
alternatives sketched in the feasibility study is chosen for development. In systems analysis, the existing information processing
procedures are documented in detail.
During requirements analysis, designers attempt to learn what users
expect a new system to do. One major
task during this phase is to define the boundaries of the system. Does the
problem concern only inventory control, or should any new system also consider
problems in purchasing when inventory
has to be replenished? During analysis,
data are also collected on the volume of transactions, decision points, and
existing files. The most challenging and creative part of the life cycle is
the design of a new system. One approach
to this task is to develop an ideal system relatively unconstrained by cost or
technology. The ideal system is then
refined until it becomes feasible. Designers must prepare detailed
specifications for the system being designed.
They specify the exact logic to be followed in processing and the
contents structure of the file.
Designers select input and output methods, and develop the formats for
input and output. These requirements for
processing, inputs, and outputs lead to the specification of programming
requirements, which can be turned over to a programming staff for coding. Table: The Systems Life Cycle
In the building stage, we develop the components needed to
construct the system. Often this involves writing computer programs to perform
the logical operations of processing. In some firms, this task is done by a
separate group of programmers. Other
organizations use analyst-programmers: The same individuals who perform the
systems analysis and design also code the resulting programs. Programs have to be tested carefully, first
as units and then in combined modules.
Usually a programming task is broken down into a series of smaller
sub-tasks or modules. All the individual
modules must operate together if the system is to work properly. During the final stage of testing, there will be some type of acceptance test in
which users verify that the system works satisfactorily. Since one purpose of the new information processing system
is to change existing procedures, training is crucial. All individuals have to understand, what is
required by the new system. When
training has been completed, it is possible to undertake conversion; it may be
necessary to write special programs to convert existing files into new ones or
to create files from manual records. Finally,
after all these stage, a team install the system. The system now operates on a routing basis. This does not mean we do not change the
system, however; there is constant need for maintenance and enhancements. Maintenance is required because programs
inevitably have errors that must be corrected when they appear. Because of the creative nature of design,
users and the IS staff may have not
communicated accurately, so certain aspects of the system must be modified as
operational experience is gained. As
users work with the system, they will learn more about it and will develop ideas for changes and
enhancements. It is important to spend
adequate time in analysis and design rather than rushing in to
development. If a system is well
specified, there are fewer changes during programming. These later changes often require major
redesign of programs and files, a very time-consuming and costly process. The
entire systems life cycle can be compared to constructing a building. Changes
are relatively inexpensive in the early, conceptual stages. They become a little more expensive at the
blueprint stage and exorbitant once the walls are erected. Systems changes are much the same. In the
conceptual stages of analysis and design, they are reasonable. However, while programs are written and some
are complete, major design changes have the potential for creating huge time
and cost overruns. |