Iterated waterfall model

Iterated Waterfall and Spiral Model. The iterated waterfall model is, as its name indicates, a modification of the waterfall model that allows programmers to redo a step of the waterfall model. When personal computers became a mainstay in the business world, programmers often had to return to earher steps in the waterfall model and could not finish each step completely. 

This development model is based on the idea that when risks are prominent, the prudent way to proceed is by a series of iterations where each cycle involves carrying out activities that explore the problem domain and or develop potential solutions in more detail. Each iteration is completed by a control process where the desirability of the next iteration is considered. Each iteration is more detailed and involves a bigger commitment of resources, but should have an increased probability of a successful overall outcome. This model is compatible with a waterfall model if provision is made at the end of each step in the waterfall for the consideration of the advisability of either continuing the project or abandoning it. 

The spiral model of software development, introduced by Barry Boehm in 1987, yms the next modification of the waterfall model. Boehm observed that rather than iterating the steps of the waterfidl model, it made more sense to view the process of software development as a spiral of steps, many of which were the steps of the waterfall model. By placing the steps in a spiral, Boehm was able to select subsets of the waterfall model to repeat that more closely followed the actual software development process. 

Ella now turns to the first slideshow that she sent out. The starting point is a description of the interaction design process. She also shows the more formal backend process, displaying the many gates with which Volvo typically operates. But there are differences in the way the different departments work. Ella explains that in her experience, the Design department works more iteratively, whereas the Software department works more according to the waterfall model. ... 

The spiral life cycle model is a repeating waterfall form at successive levels of detail. In addition, it may accommodate unforeseen events by a risk-driven approach. Similar tasks but with different objectives are performed during each cycle iteration. The inner cycles carry out more evaluation and prototyping tasks, while the outer cycles deal with final design. The cumulative cost versus time is measured at each level. These characteristics make this life cycle a generic design frame, both in feasibility studies and technical proposals, as well as in contractor engineering projects. 

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