The following are based on the waterfall model:
Classical waterfall modelIterative waterfall modelV model.Prototype model
What are the major difficulties of the waterfall based models?
Difficulty in accommodating change requests during development. In reality, 40% of the requirements change during development.High cost incurred in developing custom applications.Heavyweight processes:Lots of documentations are produced at each phase and it has been reviewed.It has been noticed that 50% of the time, people involved in documentations.Requirements for the system are determined and documented at the start are assumed to be fixed from that point on. And entire long term planning is made based on the initial frozen requirements.
Fred Brooks: The assumption that one can specify a satisfactory system in advance, get bids for its construction, have it built, and install it. This assumption is fundamentally wrong and many software acquisition problems spring from this.
In response to the shortcoming of the waterfall model, these models were proposed:
Incremental modelRapid Application Development modelEvolutionary model
Detail description and discussion (Optional)
There are some severe shortcomings of the waterfall model because of which they are not as popular as they were about 30-40 years back. The main problem that is being faced is that the type of project that is being handled are different from those that were handled 30-40 years back. Now, the projects are short and the code is not written from scratch because a lot of code is being reused and only small modifications and tailoring is done which we called as service-oriented software.
The major difficulties of the waterfall-based models:
The first problem is that there is no way change requests can be handled. The requirements are gathered up front and documented, it is assumed that this will not change, and then the plan is made based on these documented requirements, the design is done on these requirements and then coding and testing is done with respective these requirements. But then, in reality, the present projects the requirements keep on changing as development proceeds. Typically about 40 to 50 percent of the requirements change after the initial requirement specification.
The second problem is that many of the projects now are for customizing applications as already mentioned about the service-oriented software where the organization has some software and would tailor it for the specific needs of another customer. If we use the waterfall model for these custom applications there will be a huge cost because the entire thing has to be documented, specification laid out, design, and so on.
The third problem is that the waterfall model is called a heavyweight process because a lot of documentation is produced as part of the process. These are starting from requirement specification, the reviews, review results, the design various types of plans everything is to be documented and that is the reason these are called heavyweight processes. And it is estimated the typically 50 percent of the effort by a development team goes towards creating documents and naturally the project costs increase and project delays.
Reference:
Fundamentals of Software Engineering Book by Rajib Mall.Wikipedia
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