Verification and Validation

These two parts of systems engineering may be defined as follows [7.1].

Verification. The confirmation that products and processes of each development phase fulfill the requirements for that phase, and interoperate with the results of an earlier phase.

Validation. The confirmation that requirements are correct and that all products and processes, when taken in combination, satisfy all system-level mission needs.

It will be recalled, from the beginning of this chapter (i.e., Figure 7.1), that the four key elements that make up the systems engineering process, according to the Military Standard 499B as well as other approaches, are:

1. Requirements analysis

2. Functional analysis/allocation

3. Synthesis

4. System analysis and control

From the perspective of the Institute of Electrical and Electronics Engineers' (IEEE) systems engineering standard [7.23], a fifth element needs to be added to the above four elements, namely, verification and validation (V&V). This is an important step, coming as it does from this well-respected and influential source. The IEEE definitions of verification and validation, which may be compared with the above definitions, are these:

Verification. The ''process of determining whether or not the products of a given phase of development fulfill the requirements established during the previous phase.''

Validation. The ''process of evaluating a configuration item, subsystem, or system to ensure compliance with system requirements.''

Although the concepts of verification and validation (V&V) may well have been established during the early days of missiles and space technology, they have become part and parcel of today's world of systems engineering. They can be carried out as an integral part of a given contractor's systems engineering activities, or they may be executed by a third party, in which case they would likely be called independent verification and validation (IV&V).

V&V are to be a part of each and every phase of an overall development effort, focusing on the special needs and requirements of each phase. For example, within an agency such as NASA, V&V would be scheduled to deal with each of the key phases [7.24], as below:

• Phases A/B. Preliminary analysis and definition

• Phase D. Development

Further, some of the important methods that could be used to perform V&V include [7.24]:

1.

Testing

2.

Analysis

3.

Demonstration

4.

Similarity

5.

Inspection

6.

Simulation and modeling

7.

Validation of records

V&V has also been specialized to the development of software whenever this aspect of a program has been considered to be of especially high risk, since the main purpose of V&V is to try to reduce the risk in a program. In such a case, the life cycle of interest may be narrowed, typically dealing with the software phases cited below:

• Requirements

• Development and coding

• Integration and test

A more complete set of software phases, including variations that depend upon the software development model that is selected, is cited in Chapter 10, which deals with various aspects of software engineering. Further, an excellent discussion of V&V in the context of software development is provided in John Wiley's Encyclopedia of Software Engineering [7.25].

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