Prototyping

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             The purpose of prototyping based development process is to fight the first limitation of the waterfall model. The basic idea here is that instead of freezing the requirements before a design or coding can proceed, a disposable prototype is built to help you understand the requirements. Prototype development experience designing, coding, and testing, but each of these phases is not done very formally or thoroughly. By using this prototype, the client can get the actual feel of the system, which can enable clients to better understand the requirements of the desired system.    
Figure. The prototyping model.



           Prototyping is an attractive idea for complicated and large systems for which there is no manual process or existing system to help determine the requirements. Prototype development usually begins when the initial version of the specification requirements document has been developed. Once the prototype has been developed, end-users and clients are given the opportunity to use and explore a prototype. Based on their experience, they provide feedback to the developers about the prototype. benefits from more change and obtain feedback system is comparable to the cost and time involved in making changes and get feedback. Based on the feedback, the initial requirements were modified to produce the final requirements specification, which is then used to develop a system of production quality.

           In prototyping, a prototype is to be disposed of, there is no point in implementing parts of the requirements are well understood. Therefore, the focus of development is to include features that are not understood correctly. Overall, prototyping is suitable for projects where it is difficult to determine the requirements and low confidence in the stated requirements. in such projects where the requirements are not understood at first, using the model of the prototyping process can be the most effective method for developing software. It is also an excellent technique for reducing some types of risk associated with the project. Because testing consumes a major portion of development expenditure during the regular software development, it has a considerable impact in reducing costs. by using a type of cost-cutting methods, it is possible to keep the cost of the prototype for less than a few percent of the total development costs. 
            And the back of this huge additional costs. First, the experience of developing the prototype will reduce the cost of the actual software development. Second, the requirements will be more stable now because of the feedback from the prototype, there will be little change in the requirements. therefore the costs incurred due to changes in the requirements will be much reduced. Third, the quality of the final software will probably be far superior, because engineers have the experience gained while developing the prototype will allow them to create better design, write better code, and do a better test. And finally, develop a prototype alleviate many risks involved in a project where requirements are not known

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