Waterfall approach

Life-cycle models can be used to manage the elaboration of complex projects [1]. A simple but efficient model can be built up on the basis of a waterfall approach. This indicates that the project sequencing should be organized so as to avoid excessive feedback between phases, and in particular to upset the architectural design. More sophisticated approaches, such as V-cycle or spiral models, could be used to handle projects requiring more flexibility and uncertainty, as in the case of software technology. 

The development methodology establishes detailed discrete work products, by phases and events, and by associated activities. The computer systems development approach must be consistent with the selected SLC the most common development methodologies are the Waterfall Model, the Incremental Development Model, the Evolutionary Model, the Object Oriented approach, and the Spiral Model. Sample SLC activities and work products are detailed in Appendix E. 

The validation activities presented in this book can be implemented in accordance with a number of life-cycle methodologies. The waterfall model hfe cycle is the most rudimentary approach and basically cascades the activities presented in Chapter 6 through Chapter 12 inclusive. The ordered sequence of the waterfall life cycle works well with tightly defined and understood requirements. Unfortunately, in the real world, although we might like to think otherwise, most projects are not tightly defined and understood. 

The above description of a waterfall model seems simplistic, but in fact expresses deliberately the key features of a systemic approach of a complex problem. The phases must be clearly defined such as the output of one falls cleanly into the input of the next. 

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. 

Design integrity is the first step to usable systems. It is not known if a design is a good one until its implementation has failed or succeeded. Spiral development (an evolutionary approach) as opposed to waterfall development (where each phase of development is completed before the next phase is begun) helps address some of this issue. Usually, a system design is based on short-term considerations because knowledge is not reused from previous lessons learned. Development, ultimately, is driven toward failure. 

Given the constraints mentioned above, the last approach was undertaken. Compared with well known software development paradigms, we considered the first three approaches to be somewhat too waterfalling whereas the last to be more agile . In the first case, according to our past experience, we felt that spending too much time working alone with the CB is not worth the effort because this isolation away from the BUs has the risk to bias the results towards aspects that have little relevance or... 

The project execution layer is typically controlled by some product development lifecycle model (PDLM). Some PDLMs widely used for software development are the Waterfall model, Spiral model, Agile model and the Unified Process. Due to the large variety of businesses and products within the ABB Group one cannot find one single development life cycle model which is actually being used company-wide. Through the years, each business unit adopted its own approach based not only on the type of product but also on several other factors like market type, country, early company know-how, past experiences, development team culture, etc. 

General process models often fail to answer the questions, how to enter the V-, the spiral- or the waterfall-process model. Which aspects need to be considered so that activities within a V-cycle can be planned and intermediate targets defined or maturity of quality factors could be considered The aim is to show a general approach or procedures that can be considered in each phase of the product development or represent the foundation for development activities in general. 

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