Plan Driven Development
Plan-driven development, commonly known as waterfall methodology, is a software engineering approach that emphasizes comprehensive upfront planning and sequential execution. The methodology divides development into distinct phases—typically requirements gathering, design, implementation, and testing—where each phase must be largely completed before the next begins. This linear progression prioritizes predictability, control, and thorough documentation throughout the development lifecycle.
Core Characteristics
The approach requires detailed specifications and planning documents to be completed early in the project. Requirements are formally captured, analyzed, and approved before design work commences. Similarly, design must be substantially finalized before developers begin implementation. This sequential dependency means that discovered issues or requirement changes in later phases can be costly and time-consuming to address, as they may necessitate revisiting earlier work.
Applicability and Constraints
Plan-driven development works best for projects with well-understood requirements, stable scope, and clear success criteria. It has proven effective in domains such as aerospace, defense, and safety-critical systems where regulatory compliance and extensive documentation are mandatory. However, the approach struggles with projects requiring frequent iteration, rapid adaptation, or where requirements are expected to evolve—contexts increasingly common in modern software development and AI agent systems where requirements and capabilities may be discovered iteratively.