the waterfall model was the first process model to be introduced. in a waterfall model, each phase must be completed before the next phase can begin and there is no overlapping in the phases. this means that any phase in the development process begins only if the previous phase is complete. in this waterfall model, the phases do not overlap. in “the waterfall” approach, the whole process of software development is divided into separate phases. system design − the requirement specifications from first phase are studied in this phase and the system design is prepared. implementation − with inputs from the system design, the system is first developed in small programs called units, which are integrated in the next phase. integration and testing − all the units developed in the implementation phase are integrated into a system after testing of each unit. deployment of system − once the functional and non-functional testing is done; the product is deployed in the customer environment or released into the market.
maintenance − there are some issues which come up in the client environment. maintenance is done to deliver these changes in the customer environment. all these phases are cascaded to each other in which progress is seen as flowing steadily downwards (like a waterfall) through the phases. every software developed is different and requires a suitable sdlc approach to be followed based on the internal and external factors. some situations where the use of waterfall model is most appropriate are − the advantages of waterfall development are that it allows for departmentalization and control. each phase of development proceeds in strict order. the disadvantage of waterfall development is that it does not allow much reflection or revision. not suitable for the projects where requirements are at a moderate to high risk of changing. integration is done as a “big-bang.
the waterfall model is a breakdown of project activities into linear sequential phases, where each phase depends on the deliverables of the previous one and corresponds to a specialization of tasks.  thus the waterfall model maintains that one should move to a phase only when its preceding phase is reviewed and verified.
it is perhaps for this reason that the waterfall model is used as a beginning example of a development model in many software engineering texts and courses.  designers may not be aware of future difficulties when designing a new software product or feature, in which case it is better to revise the design than persist in a design that does not account for any newly discovered constraints, requirements, or problems.  while advocates of agile software development argue the waterfall model is an ineffective process for developing software, some sceptics suggest that the waterfall model is a false argument used purely to market alternative development methodologies.
the waterfall model illustrates the software development process in a linear sequential flow. this means that any phase waterfall model is a sequential model that divides software development into pre-defined the waterfall model is a breakdown of project activities into linear in software development, it tends to be among the less iterative and flexible approaches, as progress flows in largely one direction, . definition: the waterfall model is a classical model used in system development life cycle to create a system with a linear and sequential approach. it is termed as waterfall because the model develops systematically from one phase to another in a downward fashion.
in “the waterfall” approach, the whole process of software development is divided into separate process, actions and results are very well documented. reinforces good habits: define-before- design, waterfall model is an example of a sequential model. in this model, the software development activity,
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