SYSTEMS LIFE CYCLE
The Systems Life Cycle
is the oldest method for building information systems and is still used today
for complex medium or large systems projects. This methodology assumes that an
information system has a life cycle similar to that of any living organism,
with a beginning, middle, and an end. The life cycle for information system has
six stages: project definition, systems study, design, programming,
installation, and post-implementation. Each stage consists of basic
activities that must be performed before the next stage can begin.
The life cycle
methodology is a very formal approach to building systems. It partitions the
systems development process into distinct stages and develops an information system
sequentially, stage by stage. The life cycle methodology also has a very formal
division of labor between end users and information systems specialists.
Technical specialists such as systems analysts and programmers are responsible
for much of the systems analysis, design, and implementation work; end users
are limited to providing information requirements and reviewing the work of the
technical staff. Formal sign-offs or agreements between and users and technical
specialists are required as each stage is completed.
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Product or output of each stage of the life cycle that is the basis for such sign-offs. The project definition stage results in a proposal for the development of a new system. The systems study stage provides a detailed systems proposal report outlining alternative solutions and establishing the feasibility of proposed solutions. The design stage results in a report on the design specifications for the system solution that is selected. The programming stage results in actual software code for the system. The installation stage outputs the results of tests to assess the performance of the system. The post-implementation stage concludes with a post-implementation audit to measure the extent to which the new system has met its original objectives. We now describe the stages of the life cycle in detail.
STAGES OF THE SYSTEMS LIFE CYCLE
The project definition stage tries to answer the questions, “Why do we need a new system
project?” and “What do we want to accomplish?” This stage determines whether
the organization has a problem and whether that problem can be solved by building
a new information system or by modifying an existing one. If a system project
is called for, this stage identifies its general objectives, specifies the
scope of the project, and develops a project plan that can be shown to
management.
The systems study stage analyzes the problems of existing systems (manual or automated)
in detail, identifies objectives to be attained by a salutation to these problems,
and describes alternative solutions. The systems study stage examines the feasibility
of each solution alternative for review by management. This stage tries to answer
the questions, “What do the existing systems do?” “What are their strengths, weakness,
trouble spots, and problems?” “What user information requirements must be met
by the solution?” “What alternative solution options are feasible?” “What are their
costs and benefits?”
Answering these questions
requires extensive information gathering and research; sifting through
documents, reports, and work papers produced by existing systems; observing how these systems work; polling
users with questionnaires; and conducting interviews. All of the information
gathered during the systems study phase will be used to determine information
system requirements. Finally, the systems study stage describes in detail the
remaining life cycle activities and the tasks for each phase.
The design stage produces the logical and physical design specification for the solution.
Because the life cycle emphasizes formal specifications and paperwork, many of
the design and documentation tools, such as data flow diagrams, structure charts,
or system flowcharts are likely to be utilized.
The programming stage translates the design specifications produced during the design
stage into software program code. Systems analysts work with programmers to
prepare specifications for each program in the system. These program specifications
describe what each program will do, the type of programming language to be
used, inputs and outputs, processing logic, processing schedules, and control statements
such as those for sequencing input data. Programmers write customized program
code typically using a conventional third-generation programming language such
as COBOL or FORTRAN or a high-productivity fourth-generation language. Since
large systems have many programs with hundreds of thousands of lines of program
code, entire teams of programmers may be required.
The installation stage consists of the final steps to put the new or modified system into
operation: testing, training, and conversion. The software is tested to make
sure it performs properly from both a technical and a functional business
standpoint. Business and technical specialists are trained to use the new
system. A formal conversion plan provides a detailed schedule of all of the activities
required to install the new system, and the old system is converted to the new
one.
The post-implementation
stage consists of using and evaluating the system
after it is installed and is in production. It also includes updating the
system to make improvements. Users and technical specialists will go through a
formal post implementation audit that determines how well the new system has
met its original objectives and whether any revisions or modifications are
required. After the system has been fine-tuned it will need to be maintained
while it is in production to correct errors, meet requirements, or improve
processing efficiency. Over time, the system may require so much maintenance to
remain efficient and meet user objectives that it will come to the end of its
useful life span. Once the system’s life cycle comes to an end, a completely
new system is called for and the cycle may begin again.
The above stages can be
divided into three broad categories.
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