V-model

thumb|420px|The V-model of the systems engineering process.

The V-model is a graphical representation of a systems development lifecycle. It is used to produce rigorous development lifecycle models and project management models. The V-model falls into three broad categories, the German V-Modell, a general testing model, and the US government standard.

The V-model summarizes the main steps to be taken in conjunction with the corresponding deliverables within computerized system validation framework, or project life cycle development. It describes the activities to be performed and the results that have to be produced during product development.

The left side of the "V" represents the decomposition of requirements, and the creation of system specifications. The right side of the "V" represents an integration of parts and their validation. However, requirements need to be validated first against the higher level requirements or user needs. Furthermore, there is also something as validation of system models. This can partially be done on the left side also. To claim that validation only occurs on the right side may not be correct. The easiest way is to say that verification is always against the requirements (technical terms) and validation is always against the real world or the user's needs. The aerospace standard RTCA DO-178B states that requirements are validated—confirmed to be true—and the end product is verified to ensure it satisfies those requirements.

Validation can be expressed with the query "Are you building the right thing?" and verification with "Are you building it right?"

Types

There are three general types of V-model.

V-Modell

"V-Modell" is the official project management method of the German government. It is roughly equivalent to PRINCE2, but more directly relevant to software development. The key attribute of using a "V" representation was to require proof that the products from the left-side of the V were acceptable by the appropriate test and integration organization implementing the right-side of the V.

General testing

Throughout the testing community worldwide, the V-model is widely seen as a vaguer illustrative depiction of the software development process as described in the International Software Testing Qualifications Board Foundation Syllabus for software testers. There is no single definition of this model, which is more directly covered in the alternative article on the V-Model (software development).

US government standard

The US also has a government standard V-model. Its scope is a narrower systems development lifecycle model, but far more detailed and more rigorous than most UK practitioners and testers would understand by the V-model.

Validation vs. verification

It is sometimes said that validation can be expressed by the query "Are you building the right thing?" and verification by "Are you building it right?" In practice, the usage of these terms varies.

The PMBOK guide, also adopted by the IEEE as a standard (jointly maintained by INCOSE, the Systems engineering Research Council SERC, and IEEE Computer Society) defines them as follows in its 4th edition:

"Validation. The assurance that a product, service, or system meets the needs of the customer and other identified stakeholders. It often involves acceptance and suitability with external customers. Contrast with verification."
"Verification. The evaluation of whether or not a product, service, or system complies with a regulation, requirement, specification, or imposed condition. It is often an internal process. Contrast with validation."

Objectives

The V-model provides guidance for the planning and realization of projects. The following objectives are intended to be achieved by a project execution:

Minimization of project risks: The V-model improves project transparency and project control by specifying standardized approaches and describing the corresponding results and responsible roles. It permits an early recognition of planning deviations and risks and improves process management, thus reducing the project risk.
Improvement and guarantee of quality: As a standardized process model, the V-model ensures that the results to be provided are complete and have the desired quality. Defined interim results can be checked at an early stage. Uniform product contents will improve readability, understandability and verifiability.
Reduction of total cost over the entire project and system life cycle: The effort for the development, production, operation and maintenance of a system can be calculated, estimated and controlled in a transparent manner by applying a standardized process model. The results obtained are uniform and easily retraced. This reduces the acquirer's dependency on the supplier and the effort for subsequent activities and projects.
Improvement of communication between all stakeholders: The standardized and uniform description of all relevant elements and terms is the basis for the mutual understanding between all stakeholders. Thus, the frictional loss between user, acquirer, supplier and developer is reduced.

V-model topics

thumb|320px|Systems engineering and verification.

Systems engineering and verification

The systems engineering process (SEP) provides a path for improving the cost-effectiveness of complex systems as experienced by the system owner over the entire life of the system, from conception to retirement.

The US V-model, as documented in the 1991 proceedings for the National Council on Systems Engineering (NCOSE; now INCOSE as of 1995), created by Hughes in 1963 and used until Hughes was divested by the Howard Hughes Medical Institute in 1985.
The US Department of Defense puts the systems engineering process interactions into a V-model relationship.

It has now found widespread application in commercial as well as defense programs. Its primary use is in project management

The V-model provides concrete assistance on how to implement an activity and its work steps, defining explicitly the events needed to complete a work step: each activity schema contains instructions, recommendations and detailed explanations of the activity.

Limitations

The following aspects are not covered by the V-model, they must be regulated in addition, or the V-model must be adapted accordingly:

The placing of contracts for services is not regulated.
The organization and execution of operation, maintenance, repair and disposal of the system are not covered by the V-model. However, planning and preparation of a concept for these tasks are regulated in the V-model.
The V-model addresses software development within a project rather than a whole organization.