Waterfall Model: Definition & Example

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  • 0:01 A Phased Approach
  • 1:24 Requirements
  • 2:09 Design & Implementation
  • 3:41 Verification,…
  • 4:58 Advantages & Disadvantages
  • 5:33 Lesson Summary
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Lesson Transcript
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 approach to project management is one of several different methodologies. In this lesson, we'll learn the phases of the waterfall model and the advantages and disadvantages to using it.

A Phased Approach

As the new project manager at a software company, your first assignment is a simple software development project. The requirements are clearly laid out, the customer base is small, and the customer is unlikely to change the initial requirements. Knowing several different project management models will serve the purpose, how do you choose which one to use?

Of the many project management models in use today, the waterfall model is one of the most easily understandable and manageable models. The waterfall model is a project management methodology based on a sequential design process. Much like a waterfall filling lower level pools, phases in the waterfall model flow from one to another. Also like the pools filling completely before water spills into the next pool, the waterfall model finishes one phase before another phase can begin.

Developed as a software development life cycle model, waterfall methodology lends itself to projects that are small in size and whose requirements can be definitively determined up front. A simple waterfall model has 6 phases: requirements, design, implementation, verification, deployment, and maintenance. Let's go through each, starting with requirements.

Requirements

Because the waterfall model mandates that requirements be well documented before any other project work can begin, this phase is emphasized and the project manager is likely to spend more time during this phase than the others. Gathering requirements starts with the concept, or the idea of what the customer wants to do. The project manager will discuss the concept with the customer, with subject matter experts, and with other stakeholders to define very specific business needs the software will address, problems the software will resolve, and functionalities the customer desires. These requirements are captured in the requirements document, and the document is approved, closing the requirements phase before the project team moves to the next phase.

Design & Implementation

With the requirements in mind, the project team designs the software to meet the stated business needs and solve identified problems. The design phase includes the logical design and the physical design.

The logical design is an abstract representation of how the software data flows, the inputs, and the outputs. It is often shown graphically as a diagram showing data flow. The physical design determines the hardware, such as storage and network hardware, which will make the logical design a reality.

Once the design is fully complete, the project team will review and approve the design. Implementation cannot begin until the design phase is formally closed with the approval of the design document.

Once the design is approved, the implementation phase begins. Contrary to its name, the implementation phase is not when the software is implemented into the user environment. Rather, the implementation phase is building the design into actual software. During this phase, the software programmers do the actual coding to build the software according to the design document.

As with all phases in the waterfall model, the implementation phase must be complete before the next phase, verification, can begin. Often, software is built in units and integrated into a whole at a later point. This allows for ongoing implementation and verification. As one software unit implementation is complete, it is sent to verification and another software unit implementation begins.

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