What Is the V-Model in Software Development? A UK Guide

In the V-model in software development, the team is supposed to come up with its requirements and test plans beforehand. Early review can reveal missing/inclear requirements, while later changes may require updates to approved specifications and related tests.

This guide explains the V-model in the software development life cycle, its phases, and how it compares with Waterfall and Agile. It will also help you understand when the testing approach that comes with this method is worth the extra planning efforts.

The table summarises the V-model’s structure, main benefits and limitations to help businesses assess its suitability before examining each phase in detail.

Proficient software development teams can help businesses implement the V-model without unnecessary documentation or approval processes. When searching for the leading software development companies in the UK, look for suppliers with background in managing changes in projects with strict quality needs.

The V-model is a sequential method of software development where the requirement and design processes are associated with testing phases. It helps structure the software development life cycle and supports planning verification for each requirement before implementation.

“What is the V-model in the software development life cycle?” and how does it differ from a simple sequence of development stages? The distinction lies in how needs and design activities are linked to corresponding tests, as illustrated by the V-shaped diagram:

• Left side – specification and design. The teams identify the business needs, define the system architecture, and decompose the software into smaller pieces.
• Bottom – implementation. The developers implement the software according to the approved designs and specifications.
• Right side – testing. The teams conduct unit testing, integration testing, acceptance testing, and system testing for the implemented software in relation to its design and specifications.

Where the V-model comes from

The V-model evolved from some similar engineering models in Germany and in the USA in the 1980s. The German V-Modell has its roots in defence software projects and was accepted by the Federal Ministry of the Interior for civilian federal administration in summer 1992.

As opposed to the linear methodology, Agile software development involves iterations whereby one can review the product and refine requirements during development.

V-model links the process of verification and validation in the software development life cycle.

Verification phases: Deciding what to build

The left part of the V-model flows from business requirements to more technical specifications, all the way down to coding:

• Business requirements. The team determines the business issues that must be solved by the software and develops criteria for acceptance.
• System design. Software developers determine the general functions, behaviour, and interactions of the software system.
• Software architecture design. The group will define the way major components will interact with one another.
• Component/module design. Coders will define the way the components will behave and operate.
• Coding. Experts implement the designed components to create the software modules that will be tested.

The difference between verification and validation in software development becomes more apparent in situations where the system adheres to all the technical specifications but does not meet a basic need of the users.

Validation phases: Testing what was built

The right side of the V model moves from testing components individually to software testing strategies for the complete product.

In V-model testing, test cases may be developed even before the creation of the software components. This enables team members sufficient time to understand the expected output, develop test data, and determine the environment for executing the tests.

The V-model in software testing helps experts examine failures at various levels before deciding whether to accept the product. The component can pass the unit test but fail during data exchange with other components.

When you choose a software development company, ask about the developer team’s approach to planning tests, requirements traceability, and recording acceptance tests. This is a way of determining whether the company is capable of providing the required documentation for your project qualifications.

The primary challenge for business owners is the balancing act between the work that goes into planning and the expenses involved in changing plans at a later stage. The specification of approval stages will limit project scope; however, changes to the specifications also mean more approvals.

Advantages you can expect to receive from adopting this model

• Early identification of gaps in requirements. Going through the specifications and designing tests prior to implementation will help identify any missing acceptance criteria or conflicting needs that are still relatively easy to fix.
• Set approval points. Clients can review challenges, designs, and tests at predetermined milestones, minimising conflicts about a deliverable’s readiness for acceptance.
• Predictable estimates. As long as specifications and technical dependencies are known, predefined phases allow suppliers to make more predictable estimates of the necessary work on design, implementation, testing, and approval.
• Requirements traceability. A matrix identifies the test cases associated with certain demands, the passing status of those test cases, and coverage gaps.

Main disadvantages and risks include:

• Expensive changes in requirements. Modifications in an approved requirement might need changes in the specification of that criterion as well as the design elements associated with it.
• Feedback after integration of the system. Each component could be tested individually when it is being developed; however, issues with complete processes or with the interaction between the components might become evident later on.
• User feedback is limited. The fact that certain behaviours pass predefined tests means they work in the tested situation, but it does not confirm whether customers need these functionalities.

There are two factors that should be considered before deciding whether to apply the V-model: the probability of changing requirements and the costs involved in case of failure of software development. The V-model may prove efficient in cases where the duties are fixed, and testing is obligatory.

Projects where the V-model works best

The V-model in SDLC is worth considering when your project has:

• Well-defined and unambiguous requirements. The project team can clearly determine what the software should do before development begins, without changing the agreed-upon requirements specifications.
• Agreed acceptance criteria. Each requirement is defined by measurable criteria that will be used to verify the quality of developed software.
• A mature technology stack. Developers know the technologies being used, reducing the chances of an architectural overhaul.
• High failure cost. Lack of documentation in safety-critical software applications, such as those used in medical and railway controls, can have significant financial, regulatory, or safety ramifications.

Projects where another approach fits better

You may consider an iterative approach, like Agile, when:

• Requirements will definitely change. User feedback or market research could result in modifications to the requirements or priority changes.
• Releases should be frequent. The organisation requires making changes on an ongoing basis instead of waiting for the completion of the product.
• Major uncertainties exist. Complicated integrations, unproven technology, or undefined user requirements can make the detailed specification difficult to determine.

Take, for instance, the case of a startup developing its MVP, which realises that its first customers are not using some of its features at all but requesting other new ones. Agile lets the team reallocate the backlog and test this feature in the next iteration.

Comparing the V-model and the Waterfall model can help you decide when to define test cases and acceptance criteria.

V-model vs. Agile comparison is more relevant for deciding the frequency of changing requirements. For founders, the main things to consider are testing requirements, decision points, and costs of changing approved specifications.

In industries such as healthcare and railway transportation, software providers may be required to prove they implemented and tested safety requirements. These documents allow auditors and safety evaluators to determine compliance with certain requirements, review testing documentation, and investigate any outstanding issues.

Healthcare and medical device software

IEC 62304 describes lifecycle processes for the development of medical device software, maintenance, and risk management activities. This standard does not mandate the use of the V-model nor prohibit the use of the Agile process.

Nevertheless, it can help ensure the manufacturer documents V-model verification and validation test results.

Rail and transport software

EN 50128 deals with software for railways’ control and protective systems. It suggested a V-shaped lifecycle model without enforcing it. EN 50128 is replaced in the United Kingdom by BS EN 50716:2023. For railways, the V-model in software engineering is used to link safety requirements to test evidence.

It is worthwhile to use the V-model in the software development process if requirements are agreed upon before development starts and software failure may lead to financial loss, safety risks, or other serious repercussions.

In the case of constructing an MVP, testing a novel business concept or if your features will change once you have the feedback of your users, Agile methodology might be a better fit for you. There is no need to constantly rewrite your specifications and test plans.