LESSON 21
Spiral Model
SPIRAL is an iterative approach to system development. The spiral lifecycle model is a combination of the
classic waterfall model and aspects of risk analysis. This model is very appropriate for large and complex
Information Systems. The spiral model emphasizes the need to go back and reiterate earlier steps a number
of times as the project progresses. It's actually a series of short waterfall cycles, each producing an early
prototype representing a part of the entire project. It is a circular view of the software lifecycle as opposed
to the linear view of the waterfall approach. It can incorporate other models in its various developmental
phases.
There are usually four distinct phases of the spiral model software development approach.
21.1 Determine objectives, alternatives, constraints.
•The new system requirements are defined, after a comprehensive system study of the various
business processes, in as much detail as possible. This may and usually does involve interviewing
internal and external users, preparation of detailed flow diagrams showing the process or processes
for which the IS is to be developed, the inputs and outputs in terms of how the data is to be
recorded/ entered and the form in which the results are to be presented. Controls and checks
desired to be implemented in the transactional processing procedures are also examined as they are
to become an integral part of the development. Alternative strategies, in terms of IS development
issues, to meet the determined need requirements are examined as well as constraints observed
when defining the system and need requirements are also reviewed and appropriately addressed.
•Evaluate alternatives, identify and resolve risks – This involves.
1. Risk analysis – it includes addressing any factors which may risk the successful completion of
the entire project of IS development including alternative strategies and constraints. Issues
pertaining to the possibility of the IS development not meeting, for example, user
requirements, reporting requirements or the capability of the IS development team or the
compatibility and functionality of the hardware with software. The Risk analysis and suggested
solutions to mitigate and eliminate the Risks would thus become a part of the finalized strategy
to undertake IS development.
2. Prototyping – Based upon the finalized strategy and the preliminary design, the first prototype
of the new system is then developed. This is usually a scaled-down version of the system, and
represents an approximation of the characteristics of the final product.
•Develop, verify next-level product
The prototype prepared is tested against benchmarks based on customer expectations and evaluated
risks to verify the various aspects of the development. Refinements and rectifications of the
prototype are undertaken until customer satisfaction is achieved before development of the next-
level of the product.
•Plan next phase
The preceding steps are iterated until the customer is satisfied that the refined prototype represents
the final product desired. The final system is constructed based on the refined prototype. The final
system is thoroughly evaluated and tested. Routine maintenance is carried out on a continuing basis
to prevent large-scale failures and to minimize downtime.
The various stages discussed above are shown pictorially below:
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