The difference between the Waterfall and V-model lies in their structure, approach, and features. The main distinctions between them are as follows:

Waterfall:

Linear structure: Waterfall has a strict linear structure where each project phase follows one after another without looping back to previous stages. This means that one project stage begins only after the previous one is completed.

Lack of iterations: Waterfall does not involve iterations or continuous improvement processes. The project moves from stage to stage without the possibility of going back for modifications or adjustments.

Segregated responsibilities: In Waterfall, different functional groups (e.g., analysts, developers, testers) usually work separately and are responsible for different project stages.

Higher formalization: Waterfall requires more formalization and documentation since the project must sequentially go through all stages before being considered complete.

V-model:

V-shaped structure: The V-model has a structure resembling the letter “V,” where each development stage corresponds to a respective testing stage. This creates a feedback loop between development and testing.

Parallel testing and development: In the V-model, testing and development occur in parallel, allowing teams to plan and prepare for testing at each development stage immediately. This helps improve product quality and ensure compliance with requirements.

Focus on verification and validation: The V-model emphasizes product verification and validation at each stage. Verification checks whether the product meets established requirements, while validation ensures that the product meets user needs.

Early testing: In the V-model, testing starts at the early stages of development, which allows for identifying and resolving issues earlier before they become critical. This contributes to improved quality and reduced risks.

Despite the differences between Waterfall and the V-model, both methodologies are sequential and involve a clear order of stages that the project must go through. Both methodologies are better suited for projects with relatively stable requirements and a limited level of necessary changes during development. However, the V-model is more adaptable to early problem detection and ensuring product quality due to the parallelism of testing and development.