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Waterfall Model: Methodology & Phases

Instructor: Laury Hales

Laury has taught in professional adult education settings for over 10 years and is currently working on a PhD in Organizational Psychology.

The waterfall model is a sequentially based project management process that has six standard phases. In this lesson, we'll learn specifics about the waterfall model and each of the phases.

The Waterfall Model

The waterfall model is a linear, sequential project management process. Published in 1970 by Dr. Winston W. Royce, the model was originally developed for use in software development. It has distinct phases that define how the project will proceed. Today, the waterfall model is used in a wide variety of project types and the phases are tailored as needed.

Waterfall Model Methodology

The waterfall model has defined methods, principles, and best practices that project managers adhere to when using it. These can be thought of as the 'rules' of the waterfall model. The major principles of the waterfall method are:

  • Each phase must complete before another begins
  • Once a phase is completed, it isn't revisited
  • Each phase produces comprehensive documentation

Each Phase Must Complete Before Another Begins

The defining methodology of the waterfall model is that each phase must finish before another phase starts. In fact, if you think of a waterfall tumbling off a cliff and filling staggered pools, you will be able to visualize the waterfall model process. The waterfall can't run down the whole cliff until each pool is completely filled, allowing the water to continue.

Once a Phase Is Completed, It Isn't Revisited

Like the waterfall rushing down the cliff that can't go back up the river, the waterfall model can't go backwards to a previous phase. The phases don't overlap and the project can't move backwards. Strictly speaking, if a waterfall model project must move back to a previous phase, all the work must be done from the point where the project went back. For example, if a project is nearly done and a must have requirement is identified, the project must go back to the phase in which the requirements are identified and move through each succeeding phase again.

Each Phase Produces Comprehensive Documentation

The waterfall model firmly believes in the old adage 'Measure twice, cut once.' Two of the principles of the waterfall method is to have a product with as few flaws as possible and to reduce the risks to the project as much as possible. In order to achieve those principles, each phase has comprehensive documentation that fully describes the work to be done and what was actually done during the phase. The documentation is thoroughly reviewed and approved at the end of each phase.

Waterfall Method Phases

There aren't hard and fast phases in the waterfall model, but there are some generally accepted standards. Usually, the waterfall model will have 6 phases:

  • Requirements
  • Design
  • Implementation
  • Verification
  • Deployment
  • Maintenance

Requirements Phase

During the requirements phase, the project team is looking for requirements that relate to the project, such as the business need that will be addressed by the project, the user requirements for the product being developed by the project, the constraints, and the risks will be gathered.

For example, any check ordering website you've ever used came about because check printing companies wanted to increase revenue and customer satisfaction by offering faster and easier ways to order checks. The business need was to get check ordering in the hands of customers through the Internet; the user requirements would have been to make web-based check ordering fast and easy.

Design Phase

During the design phase, the project team creates the design for the product that addresses all the requirements, constraints, and design objectives. If the product is information technology related, the design is broken into 2 major components, the logical design and the physical design.

The logical design is an abstract concept of the software showing the high level data resources and processes. The logical design addresses the actual business need, such as a check ordering website that is fast, user friendly, and cheap. A logical design generally shows diagrams without reference to specific hardware. Be careful that the project team doesn't get ahead of itself and jump into the physical design before the logical design is complete. That will lead to design flaws in the final software product.

The physical design is the nuts and bolts of how the logical design will work in the environment. It details things like data input and output, data validation, user interfaces, and data storage. The physical design is where we figure out what hardware to use to make the software design work.

In projects that aren't IT related, the design is broken out according to the best practices of the industry. For the construction industry, for example, the design would be the architectural blueprints that include building elevations, floorplans, and electrical plans.

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