The activities performed in our software development project are requirements analysis, project planning, system design, detailed design, coding and unit testing, system integration and testing. Linear ordering of activities has some important consequences. First, to clearly identify the end of a phase and beginning of the others. Some certification mechanism has to be employed at the end of each phase. This is usually done by some verification and validation. Validation means confirming the output of a phase is consistent with its input (which is the output of the previous phase) and that the output of the phase is consistent with overall requirements of the system.
The consequences of the need of certification is that each phase must have some defined output that can be evaluated and certified. Therefore, when the activities of a phase are completed, there should be an output product of that phase and the goal of a phase is to produce this product. The outputs of the earlier phases are often called intermediate products or design document. For the coding phase, the output is the code. From this point of view, the output of a software project is to justify the final program along with the use of documentation with the requirements document, design document, project plan, test plan and test results.
Another implication of the linear ordering of phases is that after each phase is completed and its outputs are certified, these outputs become the inputs to the next phase and should not be changed or modified. However, changing requirements cannot be avoided and must be faced. Since changes performed in the output of one phase affect the later phases, that might have been performed. These changes have to made in a controlled manner after evaluating the effect of each change on the project. This brings us to the need for configuration control or configuration management
The certified output of a phase that is released for the best phase is called baseline. The configuration management ensures that any changes to a baseline are made after careful review, keeping in mind the interests of all parties that are affected by it. There are two basic assumptions for justifying the linear ordering of phase in the manner proposed by the waterfall model.
For a successful project resulting in a successful product, all phases listed in this SDLC model must be performed anyway.
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