The waterfall model is the process of performing the typical software development life cycle (SDLC) phases in sequential order. Each phase is completed before the next is started, and the result of each phase drives subsequent phases. Compared to alternative SDLC methodologies such as Agile, it is among the least iterative and flexible, as progress flows largely in one direction (like a waterfall) through the phases of conception, requirements analysis, design, construction, testing, deployment, and maintenance.The waterfall model is the earliest SDLC methodology.When first adopted, there were no recognized alternatives for knowledge-based creative work.
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Waterfall model in the context of Spiral model
The spiral model is a risk-driven software development process model. Based on the unique risk patterns of a given project, the spiral model guides a team to adopt elements of one or more process models, such as incremental, waterfall, or evolutionary prototyping.
View the full Wikipedia page for Spiral modelWaterfall model in the context of Requirements engineering
In the waterfall model, requirements engineering is presented as the first phase of the software development process. Later development methods, including the Rational Unified Process (RUP) for software, assume that requirements engineering continues through a system's lifetime.
Requirements management, which is a sub-function of Systems Engineering practices, is also indexed in the International Council on Systems Engineering (INCOSE) manuals.
View the full Wikipedia page for Requirements engineering