What is the difference between Agile And V-model

Let’s say you’re a race car driver, do you want the fastest car or the most maneuverable car? It may sound like an odd question for a software development team, but finding the right balance between flexibility and efficiency is actually a foundational challenge. It’s no wonder two of the most popular software development models […]

by Dilyan Dimitrov

May 14, 2024

8 min read

difference between Agile And V-model

Let’s say you’re a race car driver, do you want the fastest car or the most maneuverable car?

It may sound like an odd question for a software development team, but finding the right balance between flexibility and efficiency is actually a foundational challenge. It’s no wonder two of the most popular software development models each focus on maximizing one of these elements.

So this all begs the question, should you invest in the V-model for software development, the Agile method for software development, or stick with the traditional versions of the old waterfall method?

There’s no single right answer for everyone, so answering this question for yourself begins with understanding each model and how its advantages and disadvantages relate to your needs,

What is the V-Model of software development?

The V in V-model ironically stands for two things at once: Verification and Validation. Derived from the more traditional waterfall model of software development, the V-model is built around associating each testing phase with a corresponding development stage and vice versa.

In other words, each time a testing phase is complete, this triggers the start of a development phase. Each time a development phase is complete, this triggers the start of a testing phase. These phases continue sequentially, avoiding the need to pause development to await the results of testing.

The result is a model for development that is exceptionally efficient at delivering software which meets a specific set of requirements.

V-model origin and history

There are actually three variations of the V-model software development process developed by the German government, the US government, and a version developed by software testers. It seems that these three versions emerged independently around the 1960s.

The goal of the model was to improve upon the waterfall model, which saw a very linear approach to development with each stage following the next. However, the need to conduct each step only after the previous one was complete resulted in costly delays, developers waiting around for work to be available, and general inefficiencies.

The V-model, by contrast, enabled verification and validation to happen at the same time, resulting in faster development processes.

V model software development examples

Let’s say your team is designing software to manage a factory that produces a type of cookie. This cookie is a classic and the way it has been produced has not changed in decades. As a result, the requirements for this software: what machines it needs to manage and coordinate, what processes it must oversee, etc. are relatively fixed.

Here, the V-model’s advantages are significant, as it can enable your team to build that software very quickly and efficiently.

On the other hand, let’s say your team has been tasked with building a piece of logistics software for a global manufacturing firm. In this case, the complexity of all the elements the software needs to account for: from weather to maintenance schedules, means that it’s far more likely that requirements may change and evolve during the development process.

In such an example, the V-model may struggle because the stakeholders will not be able to test the software and see how it meets their needs until it’s complete. By that point, they may appreciate the need to add additional features, or realize an existing feature is not as important as it initially seemed.

The difference between Agile and V-Model

The key difference between these two models is flexibility. Agile software development is built around gathering feedback from stakeholders like customers throughout the development process. That feedback is then incorporated and more feedback is gathered. 

This iterative process makes Agile very flexible. If an issue arises or the customer requirements change, the model is excellent at adapting to those changes.

The V-model, by contrast, is built around streamlining the process of delivering a specific piece of software without changing its specifications mid-way. So to get back to the racecar example from the beginning, Agile is excellent at handling difficult turns and terrain, while the V-model is built for raw speed.

So if you know precisely what you want to build from the beginning and are confident those requirements aren’t going to change, the V-model makes a lot of sense. If, on the other hand, you know those requirements are likely to change during the development process, you will want to consider using Agile instead. Essentially, are you preparing for a drag race or a track with lots of curves?

V-model Validation phase

Really understanding the V-model on a deeper level requires understanding its two key phases: validation and testing. Validation is fundamentally about confirming whether or not what has been built meets the needs of your stakeholders. This usually involves working with those stakeholders to directly confirm that the product is suitable for their needs.

This is different from verification, where you may be confirming whether or not what you’ve built complies with a specific condition, requirement, or regulation.

V-model Testing Phases

There are several types of testing within the V-model, each with its own purpose.

Module Testing

This phase involves testing each module to ensure it functions as intended. Crucially, each module is tested individually or even by dividing a single module into smaller components to determine whether any issues arise.

Integration Testing

Once individual modules have been tested, it’s necessary to combine them and test them as a group. This type of testing is designed to identify issues around how modules interact with each other.

System Testing

After integration testing is complete, the V-model progresses to system testing. Here, all of the various modules are combined to form a complete system. That system is then tested to ensure it meets the original requirements.

Acceptance Testing

The final testing phase is paired with requirement analysis so the development team can conduct a final series of full system tests and confirm the requirements are met. Once this phase is complete, the software is ready to be delivered to the final customer.

Advantages of V-model in software development

Now that you understand the fundamentals, it’s time to look more closely at the most important advantages of the V-model.

Straightforward and Efficient

While the V-model may not sound straightforward to those outside of the software development work, by clearly laying out a series of sequential steps, it’s very easy to follow. Teams always know precisely where they are, what’s coming next, and can therefore more easily get a feel for how much time and effort may be required to complete the project.

This predictability helps create efficiency because teams know exactly what steps they should optimize around. Each interaction is another opportunity to refine processes and find areas for improvement.

Decreased Risk of Rework

Finding a major issue at a late stage of development is a software developer’s nightmare. This usually results in the entire team having to go back and conduct an in-depth review of previous modules and code to identify the problem.

This rework is generally very time-consuming and expensive. But because the V-model tests and validates as the work progresses, the possibility that a problem arises late in the process is lessened dramatically. Less rework means software is created faster and with fewer resources. 

That’s not to mention the developers themselves avoiding frustrating and demoralizing work that no one really enjoys. While that may not sound as important as the cost savings, it can help translate into higher retention and happier developers, improvements that also reduce costs in their own right.

Decreased Cost of Fixing Mistakes

While this advantage is closely tied with the decreased cost of rework, it’s worth highlighting as well. By ensuring mistakes are caught as early in the process as possible, the cost of fixing those mistakes decreases significantly. This again translated into lower costs and faster development times overall.

Streamlined Testing

Prior to implementing the V-model, software developers faced a difficult challenge: when should they test? Test too often and you waste time. Don’t test often enough and you delay the vital process of catching and addressing problems. 

The V-model for software development tackles this challenge by ensuring testing happens regularly enough to find issues quickly. But because testing happens simultaneously with development, time isn’t wasted waiting for tests to occur. The result is a streamlined testing process that brings the best of both worlds, testing that is frequent and efficient.

Disadvantages of V-Model in Software Development

While the advantages of the V-model are significant, there are some important disadvantages you need to understand as well.

It’s Not Very Flexible

Many of the advantages of the V-model are built around its ability to quickly identify and address mistakes in code. However, this applies only to these kinds of bugs and errors. What this means is that the model is excellent at building software to meet a specific set of requirements.

However, major problems can arise when those requirements change. The V-model is simply not designed to adapt to shifting requirements from stakeholders. If those requirements shift, the model essentially has to restart because all of the validation that’s been done so far is no longer relevant.

In other words, the V-model avoids rework when it comes to fulfilling an unchanging set of requirements, but increases the risk of rework when requirements change. Once again this ties back to the car analogy, with speed prioritized over the ability to maneuver.

It Doesn’t Create Prototypes

A hallmark of Agile software development is the creation of Minimum Viable Products (MVPs). Here, the idea is to spend the smallest possible amount of resources to create a version of the end-product that can still perform its most foundational functions. In other words, MVPs are a kind of prototype. This MVP can then be tested with stakeholders to confirm their requirements.

The value of this step comes from the reality that the requirements stakeholders think they want are not always the requirements they actually want. Only by testing can you reliably confirm whether the software those stakeholders imagined will actually deliver the value they need at the end of the day.

While the V-model for software development has a lot of testing and validation, none of those steps are designed to function as actual MVPs. So while you are regularly confirming that the software being built meets the stakeholder’s requirements, you aren’t actually putting a version of that software into the hands of those stakeholders to confirm the validity of the requirements themselves.

As with the flexibility issue, this can mean software is delivered that technically meets the original requirements, but ultimately fails to deliver the actual value those stakeholders need. The result can be costly rework.

Which Model Is Right for You?

Ultimately, choosing the right software development model comes down to a simple question: how confident are you in your software requirements? If you’re absolutely certain that the requirements your stakeholders have for your software aren’t going to change, then the V-model makes sense. The efficiency with which it can deliver on such requirements is simply unmatched.

However, if you think there’s a chance your stakeholders’ requirements may change during the software development process, Agile is the way to go. It may not be as efficient at delivering software that meets a set of requirements, but the moment those requirements change it’s going to deliver significant time and cost savings owing to its great flexibility.

Either way, it’s important for software development to occur with experienced partners capable of handling the entire process end-to-end.

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A reader who loves writing, a marketer who loves tech, a nerd who loves sports. Dilyan, our resident writer, half-jokes that his days are filled with everything you can think of - except free time. He joined our team several years into his copywriting career - and he seems to feel at home here. Because, as he puts it, “there’s always cake at the office”.  If he doesn’t have his nose buried in a book, you can typically find Dilyan writing his latest piece, tinkering with his PC, or off swimming/cycling somewhere.