It is a linear sequential flow model.
Which flows steadily downward like waterfall. The next phase begins when the
previous phase is completed.

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Generally we cannot go back to
previous phase once it is in the next phase

It is widely known and was used in
software development

When to select this model

When projects does not change
requirements and when the requirements are well defined.


Advantages and Disadvantages



to explain to users

begin no change in requirements

Stages and
activities are well defined

Difficult to go back to previous stage

Helps to plan and schedule project

Not very cost effective

Each phase have specific deliverables

a little change can cause spending a lot
of budget and is expensive

Verification at each stage ensure
detection of errors

May require more time than actually

Structured approach

very costly



V shaped Model

It is just a
revised version of the waterfall model or you can also call it as extension of
waterfall model and instead of moving down traditionally the process steps are
bent upward after implementation and coding phase which in turn forms a V
shaped like structure but this model has early test planning.




When to select this model

When the requirements are clearly
defined and known and also you must be well aware of the software development
technologies and tools


Advantages and Disadvantages




It is simple
and easy to use

Cannot modify
inbetween phases same as waterfall model

Each phase has
specific deliverables

Changing scope
is difficult and expensive

Since test
planning is integrated which is lagged in waterfall this has higher chance of

Only developed
during the implementation phase so no prototype

Works good
when requirements are understood

Model doesn’t describe
clear path for problem found during testing phases

Verification and
validation of product at early stage

Require high
cost and time than estimated