Waterfall Model: Explaining the Basics of Development Methods for the IT Passport Exam

What is the Waterfall Model?

The waterfall model is a traditional development method that proceeds through each phase of system development in order. As the name suggests, the process flows from upstream to downstream like a waterfall. This concept was proposed by Royce in 1970 and was originally described as a critique, but it ultimately became widely adopted.

Development Flow

It proceeds in order from requirements definition to basic design, detailed design, implementation, testing, and then operations and maintenance. Detailed content on each phase is explained in The Flow of System Development Phases.

Advantages

The waterfall model has several advantages. Since all phases are predetermined, planning and progress management are easy. Another major benefit is that the completion criteria for each phase are clearly defined as deliverables. It is also suitable for large-scale development, making role division among many people clear. Additionally, because documentation is thorough, maintenance and handovers are easier.

Disadvantages

On the other hand, the disadvantages cannot be ignored. If requirement changes occur in downstream phases, redesign becomes necessary, and the cost of backtracking is high. Since working software cannot be verified until the testing phase, problem discovery tends to be delayed. It is also difficult to notice discrepancies in understanding with the client, and changes become challenging once specifications are finalized.

Suitability

Suitable Cases

The waterfall model is suitable for projects with clear requirements and few changes. It fits public-sector or large-scale SI projects where phases and deliverables are predetermined by regulations or contracts. It is also effective for large teams with many members.

Unsuitable Cases

Conversely, it is not suitable for projects where requirements change frequently. For startups that prioritize speed or cases where specifications need to be refined through ongoing client dialogue, agile development is more appropriate.

V-Model

The V-model is an extension of the waterfall model, characterized by symmetrically aligning design and testing. Requirements definition corresponds to acceptance testing, basic design to system testing, detailed design to integration testing, and implementation to unit testing.

Differences from Agile Development

Details on the differences from agile development are explained in Agile Development and Scrum.

Key Points for the IT Passport Exam

In the IT Passport exam, the order of waterfall phases is frequently tested. Questions matching advantages and disadvantages, as well as problems asking about the appropriate use of waterfall versus agile, are also common.

Typical Past Exam Question Patterns

• "Which of the following correctly describes a characteristic of waterfall development?"
• "Which development method is suitable when frequent requirement changes are expected?" → Agile

Related Terms

• System Development Phases (The Flow of System Development Phases)
• Agile Development (Agile Development and Scrum)
• DevOps (What is DevOps)

Study Tips

As a study tip, first memorize the order of phases reliably. The flow is requirements definition, basic design, detailed design, implementation, testing, and operations and maintenance. Understanding requirement stability as a criterion for judging suitable and unsuitable cases is important. Also study the correspondence relationships in the V-model.

Summary

By mastering the three points—phase order, advantages and disadvantages, and suitability—you can reliably score points on waterfall-related questions. For comprehensive practice on the Management domain, see Management Summary. For practice in an exam-like format, we recommend Mock Exams.