What is Waterfall model?

Understanding Waterfall model

A software-development methodology in which progress flows downward through phases of requirements analysis design implementation integration testing installation and maintenance. The waterfall model is a sequential linear software development approach where each phase must be completed before the next begins making it highly structured and document-driven. This contrasts with iterative approaches like Agile. In security contexts waterfall often emphasizes comprehensive security requirements and design before implementation begins. The waterfall methodology is described in standards like ISO/IEC/IEEE 12207 and various system development frameworks. Organizations implement security in waterfall through security requirements definition security architecture threat modeling security design reviews and formal security testing phases. For example a government defense contractor might use a waterfall development model for a classified system with distinct security activities in each phase including comprehensive security requirements documentation formal threat modeling during design security architecture reviews before implementation code reviews during development and extensive security testing before acceptance ensuring all security controls are properly designed and implemented before the system goes operational. Related terms Systems development lifecycle SDLC Software development methodology Secure SDLC Security requirements Requirements engineering V-model Sequential development Agile development DevSecOps.