Some form of Verification and Validation has to be used during software development under any regime but these processes should be more explicit when an organisation is working to a software quality standard. These is frequently confusion between these processes so they are defined here.
In pure versions of sequential software development models such as Waterfall and V the next development phase should not start until verification of the previous stage has been completed. In any model a stage is not completed until a satisfactory verification has been achieved. Verification at each stage involves some form of testing or review of test plans and results. For coding and integration phases dynamic testing (running the code in a test harness and with test code) should usually undertaken. This can be supplemented by static test methods such as software metrics, code inspection and static analysis tools. Requirement and design stages usually have to use static methods such as documents and diagram review. For the evolutionary and spiral development models verification of requirements and designs may also take into account dynamic testing of the prototypes.
Validation takes an overall view of the software development process and concentrates on a demonstrating that the customer requirements have been met. Validation may usefully consider the traceability of the user requirements throughout the development process.
Where feasible verification and validation should not be the responsibility of staff directly involved in the production of the software, but should be undertaken by a technically competent person not in the development team. For systems with a safety element there may be requirements that the validator and/or verifier should be independent of the suppliers organisation. The details may change according to the safety rating of the software. A typical matrix is shown below:
| Safety rating | Verifier | Validator |
|---|---|---|
| No safety aspects | supplier | supplier |
| Safety related | supplier | independent |
| Safety critical | independent | independent (not verifier) |
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