A sequential development model describes the software development process as a linear, sequential flow of activities. This means that any phase in the development process should begin when the previous phase is complete. In theory, there is no overlap of phases, but in practice, it is beneficial to have early
feedback from the following phase.
In the Waterfall model, the development activities (e.g., requirements analysis, design, coding, testing) are completed one after another. In this model, test activities only occur after all other development activities have been completed.
Unlike the Waterfall model, the V-model integrates the test process throughout the development process, implementing the principle of early testing. Further, the V-model includes test levels associated with each corresponding development phase, which further supports early testing In this model, the execution of tests associated with each test level proceeds sequentially, but in some cases overlapping occurs.
Sequential development models deliver software that contains the complete set of features but typically require months or years for delivery to stakeholders and users. Incremental development involves establishing requirements, designing, building, and testing a system in pieces, which means that the software’s features grow incrementally. The size of these feature increments varies, with some methods having larger pieces and some smaller pieces. The feature increments can be as small as a single change to a user interface screen or a new query option.