SoftwareDevelopment

SoftwareDevelopment - I. Waterfall model From Wikipedia,...

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I. Waterfall model From Wikipedia, the free encyclopedia The waterfall model is a sequential development process, in which development is seen as flowing steadily downwards (like a waterfall) through the phases of Conception, Initiation, Analysis, Design (validation), Construction, Testing and maintenance. The unmodified "waterfall model". Progress flows from the top to the bottom, like a waterfall. The first formal description of the waterfall model is often cited to be an article published in 1970 by Winston W. Royce (1929–1995), [1] although Royce did not use the term "waterfall" in this article. Ironically, Royce was presenting this model as an example of a flawed, non-working model (Royce 1970). This is in fact the way the term has generally been used in writing about software development—as a way to criticize a commonly used software practice. [2] Model In Royce's original waterfall model, the following phases are followed in order: 1. Requirements specification 2. Design 3. Construction (AKA implementation or coding) 4. Integration 5. Testing and debugging (AKA Validation) 6. Installation 7. Maintenance To follow the waterfall model, one proceeds from one phase to the next in a purely sequential manner. For example, one first completes requirements specification, which are set in stone. When the requirements are fully completed, one proceeds to design. The software in question is designed
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and a blueprint is drawn for implementers (coders) to follow — this design should be a plan for implementing the requirements given. When the design is fully completed, an implementation of that design is made by coders. Towards the later stages of this implementation phase, disparate software components produced are combined to introduce new functionality and remove errors. Thus the waterfall model maintains that one should move to a phase only when its preceding phase is completed and perfected. However, there are various modified waterfall models (including Royce's final model) that may include slight or major variations upon this process. Usage The waterfall model is widely used by such large software development houses as those employed by the U.S. Department of Defense and NASA, and for many large government projects (see "the standard waterfall model" on the Internet Archive). Those who use such methods do not always formally distinguish between the pure waterfall model and the various modified waterfall models, so it can be difficult to discern exactly which models are being used and to what extent. Supporting arguments Time spent early on in software production can lead to greater economy later on in the software lifecycle; that is, it has been shown many times that a bug found in the early stages of the production lifecycle (such as requirements specification or design) is cheaper, in terms of money, effort and time, to fix than the same bug found later on in the process. ([McConnell 1996], p. 72, estimates that "a requirements defect that is left undetected until construction or maintenance will
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SoftwareDevelopment - I. Waterfall model From Wikipedia,...

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