Differences in scope of issues: Figure 4 shows that the stage of
project objectives provides information for the establishment of
requirements. The same happens in the Figure 5 in the Spiral
Model. However it is realized that the project objectives
contributes to the phase of establishing interfaces that shows the
importance of analyzing the relationship between different parts of
the system or the relationship between different systems.
Comparison between Requirements Phase
Differences in the inter-component dependency: For the
requirements phase the Waterfall Model has two types: Establish
Requirements and Requirements Gathering while the Spiral
Model has just one: Requirements Gathering. The Waterfall
Model presents a specific type to establish requirements before
collecting it while the Spiral omits the information, it could be
interpreted that the establishment of requirements depends on the
level of the analyst's knowledge. The Waterfall Model also
specifically treats the revision of requirements, while and the
Spiral does not.
Differences in the need for human involvement: both models
need the same level of human involvement in the requirements
phase.
Differences in the development procedure: In the Waterfall
Model a stage of establishment of requirements is performed
before the actual collection, which does not happen in the Spiral
Model. It also has a procedure for definition of interfaces for the
requirements gathering. Thus, the Waterfall Model presents a
definition of requirements with more procedures than the Spiral
Model.
Differences in scope of issues: Figure 2 of the Spiral Model
presented in the Section 2 shows in the third quadrant a stage for
validation of the requirements; however, it does not specify a
revision stage. In Figure 1 of the Waterfall Model there is an input
indication for the requirements phase indicating the validation and
revision of the requirements.
Comparison between Analysis Phase
Differences in the inter-component dependency: The Waterfall
Model just presents dependences of the requirements for the