Systems Analysis,
Prototyping and Iteration
Systems Analysis
This
is a process used in the design
of new systems. Systems analysis
follows stages of investigation, design
and implementation.
Each stage should involve close
consultation with potential users, in
the various functional areas of the
organisation, to ensure that their
information and operational
requirements are met.
The
design stage should produce a
system specification, which should
detail all necessary materials and
procedures needed to fulfill the
specification.
The specification should detail all
the necessary clerical procedures,
hardware requirements and the
inputs, processing and outputs
required of the computer software.
After
implementation of a system, it
will require continual monitoring and
probably, occasional modification,
when the operational or information
requirements of users change. This
maintenance task is the responsibility
of the systems analyst.
SDM Waterfall Model
Feasibility

The feasibility study determines whether a
particular development project should go ahead. If the
project is to proceed then a project plan and budget
estimate for the other stages of development will be
produced.
Requirements analysis

The requirements for the new or modified system
are gathered at this stage. They should be recorded so
that at the end of the project the software can be
tested to ensure it fulfills the requirements.
Design specification
Design focuses on:




high level design, e.g. what programs are needed, what are their inputs and
outputs, what are their interactions with other software or the operating
system.
low level design, e.g. how will the program work, what models or algorithms
will be used, what libraries are required.
data design, e.g. for input and output, data structures in the software.
The level of detail in the design may be a matter of personal choice or may
be specified by particular development procedures. Having a detailed design
will make generating the code easier but will make changing things difficult
whereas a more broad brush design will leave more work in the
implementation phase but allows room for the details to come out as the
development progresses. Above all the design should be documented
including reasons for making particular choices if a number of options were
available. This makes it much easier for new developers to join a project and
helps when new features are required.
Coding

In this phase the designs are translated into code.
Programming tools such as compilers and quality assurance
tools are used to generate good quality source code and the
software application. Testing of small self-contained parts
(modules) of the overall application may take place depending
on the modularity of the code.
Testing

The overall system is tested to ensure that it works on
the intended platform(s), giving correct results or showing
the required behaviour defined in the requirements
document. The use of debuggers and profiling tools will be
useful at this stage to identify errors in the code and get
the best possible performance from the code. Optimum
performance is especially important in scientific computing
applications.
Maintenance

Once the system is delivered to users it will
inevitably need maintenance. There may be bugs
caused by unexpected input values (add them to a
test suite) or by unexpected (inappropriate) use of
the software (tighten up the documentation). In
addition users will want more or different
functionality and will definitely want it to run
faster or address bigger problems! The software
development process should be able to
accommodate changes at this stage through a well
thought out design and any changes should have
their own requirements, design, coding and testing
stages.
In
the waterfall model, it is possible to rework
earlier stages in the light of experience
gained at a later stage. Each stage is signed
off and the next stage is proceeded with.
However the end user is rarely involved in the
development stage, even though they may
well be involved in signing off. It is therefore
critical that the analysts and the programmers
understand the end-users’ requirements.
This can be quite difficult with the waterfall
model.
The
waterfall model has disadvantages,
which can be overcome using Prototyping, in
which a model of the system is developed in
partnership with the end-user. The features
are worked out with the end user using a
prototype, and the end user can have a
considerable input into the development of a
project.
Benefits are:
Misunderstandings
are detected at early
stages
The user will notice any missing functions,
incomplete or inconsistent requirements.
Can be built quickly to demonstrate systems
It can be used for training before the system
is finished
Drawbacks are:
Project management can be
uncoordinated or even sloppy.
Meetings with end users can become
time consuming.
The final result could be completely
different to what was requested in the
first place.
Different Methods of Prototypes
– Test the feasibility of the design
proposal
Modelling – building to develop an
understanding of the user’s requirements
Throw-away prototyping – Pilot and modelling
are throw away types – once they achieve their
purpose the real system is built.
Evolutionary prototyping – each prototype built is
a step closer to solution.
Piloting