Verification, Validation, and Testing of Engineered Systems

6.1 PURPOSE AND BASIC CONCEPTS

The purpose of this chapter is to examine difficult questions that concern anyone involved with verification, validation and testing, namely, what to test, when to test, how to test and how much to test and when to stop testing. In other words, how one should select a VVT strategy and how one should optimize it.

In this chapter, we address the above questions by presenting a VVT cost and risk model as well as a VVT time and risk model. Once such models are established, it is possible to optimize the VVT strategy to minimize quality cost, time and risk. Three VVT model variants are presented utilizing probabilistic, simulation (Monte Carlo–based) and fuzzy logic paradigms for estimating and optimizing system VVT cost, time and risk. Chapter 7 describes ways to acquire quality data and optimize the VVT strategy in the face of funding, time and other resource limitations and in accordance with different business objectives. Finally, Chapter 8 describes the methodology used to validate the quality model along with examples describing a system’s quality improvements.⁷³

6.1.1 Historical Models for Cost of Quality

Generally, there is a direct correlation between VVT investment and system quality. Early in the 1950s, two quality luminaries proposed two different qualitative models, defining “quality cost” as the sum of VVT costs plus failure costs. Joseph Juran suggested that there is an optimal VVT strategy which will yield minimum quality cost, whereas ...