Computer Based Systems

Computer Based Systems
The system Development Cycle
What is it?
The system development cycle is a method used to create a system where none has existed before and/or
modify an existing system. It is sometimes simply called System Development.


It involves a number of stages representing a standard strategy for taking a problem from start to finish.

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Two approaches:
1. Conservative-working systematically through the steps.


2. Radical-Cycling through the cycle several times until the final result is achieved.


The Steps
The above diagram shows that the system development cycle is represented by 5 broad stages:
-Requirements Definition.


-Analysis.


-Design.


-Implementation.
-Operation and Evaluation.


Requirements Definition
Also known as:
Requirements analysis or.Feasibility study.


-Duration is relatively short compared to the rest of the development cycle.


-It is important to get it right the first time else mistakes could be costly. In the worst case a large oversight
would require starting over from step one.


Aim
The aim of this stage is to see how the present system functions and to identify the nature of the problem
(problem definition). once the problem has been identified a report is compiled called a feasibility report.
that report contains – (1) Objectives of the initial study (e.g. why a mail order firm takes longer than a week
to dispatch orders). (2) depth of the initial study (e.g. Were interviews conducted with staff involved). (3)
recommendations including an outline of the proposed development (e.g. redesign current computer
system).


After studying the report management have three options – (a) geta second opinion
(b) do nothing
(c) follow recommendations.


If the investigation confirms that there is a problem further work and study may be needed.


Analysis
Aim
The aim of the analysis stage is to answer the questions who, what, when, why. The three main processes in
system analysis are (1) Data gathering, (2) Detailed analysis, (3) Report on the above findings.


Data gathering
What tasks are occurring, who is performing them, when are the tasks being performed. A range if methods
can be used to gather data including (1) Study current documentation. (2) Interview (3) Questionnaires (4)
Observation.
Questionnaires usually involve closed or open style questions.


Questionnaires
Closed questions limit responses e.g. tick a box, yes/no, multiple choice. Open questions allow free written
response. Observations
This involves a system analyst visiting the organization to view current procedures, channels of
communication and the flow of data through the organization.


Detailed analysis
at this stage data is collated , organized and analyzed. At this stage the system analyst may have an idea as
to the solution of the problem. A range of tools may be used to assist in the analyst process :- (1)
organizational charts
(2) Statistical graphs or charts
(3) data flow diagrams
(4) Flowcharts
(5) Data dictionaries
(6) decision trees
(7) Gantt chart
Organization Charts
– Illustrates the structure of the organization pictorially and shows how responsibilities are allocated within
the organization.


Exercise: Create an organization chart for either – (1) The school
(2) Some other organization you know.


Statistical graphs
Graphs such as a pie or bar chart are particularly useful in reporting the results of closed questions. A Pie
chart is much easier to interpret than a set of numbers.
Data Flow Diagrams
-Illustrates the movement of data through a system e.g.


Flowcharts
-Similar to algorithms
-It is an accepted convention that flowcharts should fit on a single page. If it doesn’t it is divided into
smaller modules (Stepwise Refinement.)
Data Dictionaries
A data dictionary is a catalogue or listening of data items used within the information system. It is used to
manage information resources and is particularly useful when working with databases e.g.



Decision tree
table
Grannt charts
A grannt chart is used to illustrate the time line for the actual system developement process. Dates for
specific stages are set and these are used to control the development process.


Analysis
Analysis examines the areas of input processing and output
Input
Method used to gather input: (1) frequency
(2) quantity
(3) accuracy
(4) cost
(5) who is involved?
Processing
(1) how data is processed
(2) processing speed
(3) frequency
(4) quantity
(5) accuracy
(6) cost
(7) who is involved
Output
Availability of output
Analysis report
This report should include: (1) statement of the problem.


(2) summary of current procedures used by the firm.


(3) summary of current problems.


(4) problems solution including feasibility, requirements, cost and the effect
on people involved.


(5) a general specification and preliminary suggestion for a problem solution.


Once again management may choose to get a second opinion or follow the recommendation and go to the
design stage.


Design
The design stage can be split into 2 broad areas:
(1) initial design.
(2) Detailed design.


For most systems the following areas should be covered:
(1) output requirements-How is output to be presented? e.g. monitor or paper,
(2) input requirements-What is the best way to obtain data e.g. keyboard ,scanner.


(3) storage requirements e.g. do we need 500meg HD or a 9mb HD, should we use a flat file or a relational
database?
(4) processing specifications-If there are large amounts of complex data you will be needed for hardware
(5) hardware/software: Final decisions are now made and equipment is purchased. The analyst seeks to
purchase software that is already available or create their own custom software and have a programmer
write one for them.


(6)Procedures and control: Procedures involve how a task is performed.control should be built into the
system to make sure data is safe and correct (is an issue of data integrity).


(7) Human factors: Ergonomics change with job descriptions and employment must be considered. All of
these factors should be reported in a design report in the final stage