What is a V-Model?

The V-Model is a model that is utilised for different development processes, such as software development. It was developed in its original form in the 1990s, refined again and again over time, and adapted to current development methods. The basic idea, however, originated in the early 1970s and was conceived as an advanced development of the waterfall model.

In addition to the particular development phases of a project, the V-Model defines the accompanying procedure for quality assurance and describes how these specific phases can be integrated. The procedure model owes its name to its V-shaped structure.

The specific V-Model phases

First of all, the V-Model defines a project course in specific phases that progressively gets more detailed:

  • At the beginning of the project, the model provides an analysis of the planned system’s general requirements.
  • After this, the project should be augmented with the functional and non-functional requirements of the system architecture.
  • This is followed by the system design, during which the system components and interfaces are designed.
  • When these phases are completed, the software architecture can be designed in detail.

Now the actual software development occurs according to these plans, followed by the quality assurance phases, which always refer to the development steps. The model includes the following tasks:

  • Unit tests
  • Integration tests
  • System integration
  • Acceptance

Interplay between concept and quality assurance

The “V” symbolizes two branches of the model. Here, the development phase is situated across from the corresponding quality assurance phases. The left arm of the letter V contains the tasks for designing and developing the system. The right arm encompasses related quality assurance measures. Located in the middle of both these arms, embedded between the development phases and quality assurance phases, is the implementation of the product. In the case of a software project, this would be software programming.

Whether the designed software architecture has been correctly implemented is checked via unit tests. During these tests, the software’s individual modules are scrutinized in-detail to assess whether they perform the required functions and actually deliver the expected results. In order to avoid errors, these module tests are usually run in parallel to development where possible.

Situated across from the system design are the integration tests, which are in place to check if the separate components work together as planned, and whether, for example, all processes yield the expected results. Erroneous results at this point can indicate problems with the interfaces, among others.

The system test checks whether the system’s general requirements – which were defined when the system architecture was designed – have been met. These tests normally take place in a test environment, which readjusts the actual conditions for users as accurately as possible.

At the end of the project, the requirements analysis of the overall system is performed. In the model, this is placed across from the acceptance of the finished product. During the final acceptance, the customer checks whether the software meets the requirements of routine operation. Here, the software behavior is normally tested on the surface, i.e. to the extent that a customer would use it on a day-to-day basis. One also refers to this as an acceptance test.

V-Model XT: the most recent advancement of the V-Model

In 2006, the V-Model was finally overhauled in order to be able to reflect principles such as agile development. The result was the V-Model XT. The XT here stands for Extreme Tailoring and refers to the added option of being able to tailor the model to a project’s specific requirements.

A fundamental idea behind the latest advancement was to provide a model that can be flexibly adapted to different project sizes. Even for smaller projects, the older method was often disproportionately time-consuming, and therefore inefficient. With the V-Model XT, in contrast, it is possible to eliminate certain phases for small projects that would require too much additional time.

Furthermore, XT includes task blocks that explicitly refer to the customer. The old model only deals with the management of the project by the contractor before it’s finally accepted. In the new model, the customer is more deeply-involved.

The model continues to be updated regularly due to ongoing innovation in the software development process and improved practicality. The latest version of the V-Model XT is Version 2.3.

The V-Model’s areas of application

The V-Model XT is a popular procedure model in the industry and is considered the official standard for IT projects by federal agencies. The V-Model is mandatory for most tenders for public-sector software projects. As such, it’s an important tool for companies that develop software for agencies and ministries. It can be used for software projects of any size, whether in commerce, the military or the public sector. The model serves as a tool to facilitate the organisation and execution of development, maintenance, and advancement of diverse IT systems.

Furthermore, the V-Model can be applied to other development areas such as electronic or mechanical systems in research and science. For these areas of application, there are lightly adapted versions that reflect the typical procedure steps of the respective sectors.

Advantages and disadvantages of the V-Model

The main reason why this development model is so popular is that it ensures high transparency and cleanly-defined, comprehensible processes. Below you’ll find an overview of the most important advantages and points of criticism.

Advantages of the V-Model

  • Optimisation of communication between participants through firmly-defined terms and responsibilities
  • Minimisation of risks and better plannability through firmly-prescribed roles, structures, and results
  • Improvement of product quality through integrated quality assurance measures
  • Cost savings through transparent reappraisal of the entire product life cycle

All things considered, the model helps to avoid misunderstandings and unnecessary work. Furthermore, it ensures that all tasks are completed at the right time and in an appropriate sequence, and that, if possible, no idle time arises.

Disadvantages of the V-model

The model is, in part, too simple to completely illustrate the development process from the developer’s point of view. The process focus is primarily on project management. Furthermore, the relatively rigid structure hardly allows one to react flexibly to changes during development, and thus encourages a comparatively linear project progression. Nevertheless, with the V-Model it is possible to practice agile development, provided that the model is properly understood and utilised.

Alternatives to the V-Model

There are various procedure models in software development that – depending on the project and team structure – are worth considering as a software development process. The selection of procedure models is relatively large, although models such as the waterfall model or spiral model are widely used. The waterfall model is to some degree best-suited for small, linear on-going projects, while the spiral model can be well-utilised in iteratively-structured projects.


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