Description¶

The V-Model (also known as the Verification and Validation model) is an extension of the Waterfall model, but with a focus on testing at every stage. Instead of going straight down like a waterfall, the process forms a "V" shape, the left side is development (verification), the right side is testing (validation), and they’re connected phase-by-phase.

V-Model Phases:¶

The V¶

graph LR
    R[Requirements] --> S[System design]
    S --> A[Architecture design]
    A --> M[Module design]
    M --> C[Coding]
    C --> UT[Unit testing]
    UT --> IT[Integration testing]
    IT --> ST[System testing]
    ST --> UAT[Acceptance testing]
    R -. verified by .- UAT
    S -. verified by .- ST
    A -. verified by .- IT
    M -. verified by .- UT

The dotted lines are the point of the model. Every design document on the way down has a named test level on the way up that proves it was satisfied, which is the traceable evidence regulated domains require.

Left Side: Verification (Planning & Design):¶

Requirements Analysis
System Design
Architecture Design
Module Design

Right Side: Validation (Testing):¶

Each development phase has a matching test phase:

Development Phase	Corresponding Test Phase
Requirements Analysis	Acceptance Testing
System Design	System Testing
Architecture Design	Integration Testing
Module Design	Unit Testing

Advantages:¶

Early testing planning improves quality.
Clear links between development and testing.
Errors can be caught early.
Better suited for high-reliability systems (like aerospace, medical software, etc.)

Disadvantages:¶

Still rigid, not great for changing requirements.
No early working prototypes.
More complex than Waterfall.

Diagrams¶

v model 1

v-model 2