# Waterfall Model for Software Engineering

> **Category**: Predictive & Gate-Driven | **Badge**: Sequential Classical

## Overview
The classic Waterfall model enforces rigid stage gates where each phase (Requirements, Architecture Design, Coding, System Testing, Deployment) must be formally approved before the next begins.

### Best Suited For
Banking & Financial core engines, Aerospace / Defense software, Medical devices, and strict fixed-bid government tenders.

### Not Recommended For
Early-stage startups, exploratory AI/ML experiments, or projects where user feedback alters the roadmap weekly.

## Key Roles & Responsibilities
- **Business Analyst / Solutions Architect**: Drafts comprehensive 100+ page Software Requirement Specifications (SRS).
- **Project / Program Manager**: Monitors Critical Path Method (CPM), phase sign-offs, and Gantt milestones.
- **Independent Verification & Validation (IV&V)**: Formal QA audits executing traceability matrices against the baseline SRS.

## Core Ceremonies & Rhythms
### Phase Gate Review (Half-Day formal meeting)
Formal sign-off audit before unlocking budget for the subsequent phase.

### Change Control Board (CCB) (Bi-weekly / As needed)
Evaluate and approve/reject any proposed scope or contract modifications.

### Milestone Acceptance Verification (Full Day)
Customer witness test and contractual compliance sign-off.

## Phases & Execution Stepper
1. **Requirement Analysis & Specification** (Phase 1): Zero code written. All business expectations, compliance, and user requirements frozen in SRS.
1. **High-Level & Low-Level Design** (Phase 2): System architecture, ER diagrams, data flow schemas, and API contracts documented.
1. **Implementation & Module Coding** (Phase 3): Developers code modules according to frozen technical specifications.
1. **Integration & System Testing** (Phase 4): Full regression, stress, penetration testing, and User Acceptance Testing (UAT).
1. **Deployment & Maintenance** (Phase 5): Production rollout followed by long-term operational maintenance and defect patch cycles.

## Default Board Workflow Blueprint
Columns: Phase 1: Requirements ➔ Phase 2: System Design ➔ Phase 3: Development ➔ Phase 4: UAT & Verification ➔ Phase 5: Release & Ops