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the level of reworking of the product is minimal and the products remain unchanged after the
completion of that stage [2]. There is no room for major changes to requirements/design etc.
as these changes may be necessary, when carrying out the further development or improving
the solution and it is clear the rigid structure of this model will not be suitable for this project.
Figure 1
The Waterfall Model [3]
2.2.2
The Spiral Model
The Spiral model differs from the waterfall model in that it introduces an iterative approach to
system development [2]. The spiral model (see figure 2) is a lot less rigid in its approach, it
allows for constant movement between levels of the development process and the life cycle of
the system. It allows you to change the requirements, re-design and re-implement with each
rotation of the spiral, this is because the models stages are cycled and reversible. However
one drawback of this model is when implemented it may lead to endless work as it is difficult
to get the system perfect and, as explained in [5], there is no clear cut stopping point when
using the spiral model.
5