spiral model combines the idea of iterative development with the systematic,
controlled aspects of the waterfall model. The spiral model has four phases. A
software project repeatedly passes through these phases in iterations called
Spirals. This means that the product is released incrementally.
Identification phase starts with gathering the business requirements in the
base spiral. In the subsequent spirals as the product matures, identification
of system requirements, subsystem requirements and unit requirements are all
done in this phase. The proof of concept includes identifying, estimating and
monitoring the technical feasibility and management risks, such as schedule
slippage and cost overrun. After testing the build, at the end of first
iteration, the customer evaluates the software and provides feedback. This
phase also includes understanding the system requirements by continuous
communication between the customer and the system analyst.
Design phase starts with the conceptual design in the baseline spiral and
involves architectural design, logical design of modules, physical product
design and the final design in the subsequent spirals. The architecture of the
application is designed in this stage, which means the structure of the
application for example UI features, such as colours, text, tabs, buttons and
links. After that each module in the application is designed and finally the
whole system is designed in the last build. The customer gives feedback on this
design in the evaluation stage at the end of the iteration.
phase refers to production of the actual software product at every spiral. In
the base spiral, the product is implemented by software developers, which code
the application so that it functions properly. The developers have to follow
the design supplied by the designers. Another build is created later on in the
development, so that new implementations could be provided, which could be more
efficient. The first build is used as a back up if the second build fails. The
build is tested in the evaluation stage.
evaluation phase consists of managing risks in the application used to to
contain and mitigate threats in the product and also testing how the
application works, which is done to make the code more efficient and reduce
errors found in the build of the product. The customer gives feedback to the
design and the build of the system, to see how the product development is being
The spiral model is applied
When the budget is low
and risks need to be evaluated
Project is medium to
Customer is not sure of
Requirements are complex
and need evaluation to get clarity.
Significant changes are
expected in the product during the development cycle.
Advantages of spiral model:
Requirements can be
Promotes the use of
Requirements can be
defined more accurately.
Users can see the system
in early stages of development.
Development can be divided
into modules and the difficult modules can be developed earlier.
Disadvantages of the model:
End of the project may
not be known early .
Management is more
Spiral may go on
Not suitable for small
or low risk projects
the many project management models in use today, the waterfall model is one of
the most easily understandable and manageable models. The waterfall model is a project
management methodology based on a sequential design process. Much like a
waterfall filling lower level pools, phases in the waterfall model flow from
one to another. Also like the pools filling completely before water spills into
the next pool, the waterfall model finishes one phase before another phase can
as a software development life cycle model, waterfall methodology lends itself
to projects that are small in size and whose requirements can be definitively
determined up front. A simple waterfall model has 6 phases: requirements
analysis, design, implementation, testing, deployment, and maintenance.
The first phase of the
waterfall model is requirement analysis and in this phase, in which the
stakeholders analyse the requirements that will be needed to create the