Waterfall Model

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The simplest model of the process is the waterfall model, which states that the phase arranged in a linear sequence. This model was originally proposed by Royce. In this model, a project started with a feasibility analysis. Having successfully demonstrated the feasibility of the project, requirements analysis and project planning begins. design starts after the requirements analysis is complete, and coding begins after the design is complete.
         Once programming is complete, the code is integrated and testing is done. Upon successful completion of testing, the system is installed. After this, the regular operation and maintenance of the system takes place. The basic idea behind the phase separation of concerns is one phase deals with a set of distinct and separate from worries. By doing this, a large and complex task of building software is divided into smaller tasks (which, by itself, is quite complex) of the specific requirements, doing design, etc. Separating concerns and focusing on a select few in phase providing better handling.Requirements analysis phase referred to as "analysis and planning." Planning is an important activity in software development. A good plan is based on the system requirements and should be done before the next stage begins. multiple certifications mechanisms to be employed at the end of each stage. This is usually done by some verification and validation means that will ensure that the output of the phase is consistent with the input (which is the output of the previous stage), and that the output of the phase is consistent with the overall system requirements.

Figure. The waterfall model


            The consequences of the need for certification is that each stage must have some defined output that can be evaluated and certified. That is, when the activities of the phase is complete, there should be a product produced by that phase. The output of the previous phase is often called the work product and are usually in the form of a document such as a requirements document or design document. For the coding phase, the output code. the following documents are generally reasonable set of the form should be produced in each project:
document requirements
- Project Plan
- Design documents (architecture, systems, detailed)
- Test plan and test report
- End of Code
- Software Manual (for example, user, installation, etc.)

         One of the main advantages of the waterfall model is its simplicity. It is conceptually simple and split a big task to build a software system is divided into a series of stages clean, each dealing with a separate phase logical concern. It is also easy to administer in-setting contracts for each phase is completed and the work products that are produced, some amount of money given by the customer to the organization evolve. Limitations on Water fall are:
1. It assumes that the system requirements can be frozen (ie, baselined) before design begins.
2. Freezing conditions usually requires choosing the hardware (because it is part of the requirements specification).
3. It follows the "big bang" approach-the whole software is delivered in one shot at the end.
4. encourages users and other stakeholders to increase even features that they think may be required (which ultimately might not get used).
5. This is a document-driven process that requires an official document at the end of each stage.

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