Software Engineering V Model

Software Engineering

V Model

The V‑model (Verification and Validation model) is an extension of the Waterfall model that emphasises testing at every development stage.
Each development phase on the left side of the V has a corresponding testing activity on the right side — hence the V shape.
The model shows clear relationships between development deliverables and test plans (e.g., system design ↔ system testing).
Testing activities begin early (test planning starts during requirements and design) rather than waiting until the end.
The V‑model works well for projects with well-defined requirements and where heavy testing and traceability are required.
It improves quality by enforcing verification at each development level and validation during corresponding test phases.

Verification and Validation

Verification

Verification checks whether the product is being built correctly — i.e., whether each phase of development meets its specified requirements. Verification activities focus on reviews, inspections and static analysis and do not require executing code.

Validation

Validation checks whether the right product has been built — i.e., whether the final system meets customer needs and expectations. Validation activities involve executing the code (unit, integration, system and acceptance testing).

Phases of the Verification Stage

Requirement Analysis: Gather and document customer requirements. Create requirement specifications that guide design and testing.
System Design: Define system architecture, hardware, communication interfaces and overall high-level design (HLD).
Module Design (Low-Level Design): Break the system into modules and specify detailed designs (LLD) for each module.
Implementation / Coding: Translate module designs into source code following coding standards and best practices.

Phases of the Validation Stage

Unit Testing: Developers execute white-box tests on individual modules. Unit tests are derived from module design.
Integration Testing: Combine modules and test interactions. Integration tests validate interfaces and behavior between components and are derived from HLD.
System Testing: Test the complete integrated system against the system design and functional/non-functional requirements.
Acceptance Testing: Final validation performed with stakeholders to confirm the system meets business needs (includes user acceptance, load and stress testing where applicable).

Advantages of the V Model

Clear structure and discipline; each phase has well-defined deliverables and corresponding test activities.
Early test planning reduces defects and improves quality.
Works well for projects with stable requirements and regulatory or traceability needs.
Improves defect detection due to early and continuous testing activities.
Easy to manage because of its rigidity and emphasis on documentation and verification.

Disadvantages of the V Model

Not ideal for large or complex projects where requirements are likely to change frequently.
Less flexible — difficult to accommodate changes once a phase is completed.
May lack early prototypes and stakeholder involvement compared to Agile approaches.
Can be costly and time-consuming for projects that require frequent changes.
Requires clear and complete requirements up front to be effective.

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