The spiral model is an iterative software development process that is used to manage risks on large, complex projects. It consists of loops called phases where the software is further developed. Each phase involves planning, risk analysis, engineering, and evaluation. This allows for new requirements to be continuously incorporated into the design and for risks to be identified and addressed throughout the project.

1. Spiral Model

2.  The exact number of loops of the spiral is not fixed
and can vary from project to project.
 Each loop of the spiral is called a phase of the
software process.
 The exact number of phases through which the
product is developed can be varied by the project
manager depending upon the project risks.
 A prominent feature of the spiral model is handling
unforeseen risks that can show up much after the
project has started.

3. Risk handling in spiral model
 A risk is essentially any adverse circumstance that
might hamper the successful completion of a software
project.
 As an example, consider a project for which a risk can
be that data access from a remote database might be
too slow to be acceptable by the customer.
 Caching scheme / Faster communication scheme.

4. 1 Phases of the Spiral Model
 Each phase in this model is split into four sectors (or
quadrants) as shown in Figure 2.12.
 Quadrant 1: The objectives are investigated,
elaborated, and analysed.
 Quadrant 2: The alternative solutions are
evaluated to select the best possible solution.
 To be able to do this, the solutions are evaluated by
developing an appropriate prototype.

5.  Quadrant 3: Developing and verifying the next level
of the software.
 Quadrant 4: Reviewing the results of the stages
traversed so far.

6. Advantages/pros and disadvantages/cons
of the spiral model
 Disadvantages:
 1. For developers – complex model to follow
 2. Counterproductive to use.
 3. Not very suitable for use in the development of
outsourced projects.
 Advantages:
 1. Much more powerful than the prototyping model.

8. Spiral model as a meta model
 The spiral model incorporates the systematic step-wise
approach of the waterfall model.
 The spiral model uses the approach of the prototyping
model.


9. A COMPARISON OF DIFFERENT LIFE CYCLE
MODELS
 The classical waterfall model can be considered as the
basic model and all other life cycle models as
embellishments of this model.
 Iterative waterfall – feedback paths. / widely used /
only for well-understood problems. not suitable for
development of very large projects.
 The prototyping model user requirements or the
underlying technical aspects are not well understood.
 All the risks can be identified before the project starts.
 User interface part of projects.

10.  The evolutionary large problems which can be
decomposed into a set of modules for incremental
development and delivery.
 object-oriented development projects
 The spiral model is considered a meta model and
encompasses all other life cycle models.

11. Selecting an Appropriate Life Cycle
Model for a Project
 1. Characteristics of the software to be developed:
 For small services projects, the agile model is favoured.
 For product and embedded software development,
the iterative waterfall model can be preferred.
 An evolutionary model is a suitable model for object-
oriented development projects.
 2. Characteristics of the development team:
 3. Characteristics of the customer: