Also known as Verification and Validation model, the V Model is an extension of the waterfall model and is based on the association of a testing phase for each corresponding development stage. This means that the V Model demonstrates the relationships between each phase of the development life cycle and its associated phase of testing. There are Verification phases on one side of the ‘V’ and Validation phases on the other side. The Coding Phase joins the two sides of the V-Model. The horizontal and vertical axes represents time or project completeness (left-to-right) and level of abstraction, respectively. This is a highly-disciplined model and the next phase starts only after completion of the previous phase.