TOPAAS: An Alternative Approach to Software Reliability Quantification

Abstract

dIn the realm of safety related systems, a growing number of functions are realized by software, ranging from 'firmware' to autonomous decision-taking software.To support (political) real-world decision makers, quantitative risk assessment methodology quantifies the reliability of systems. The optimal choice of safety measures with respect to the available budget, for example, the UK (as low as reasonably practicable approach), requires quantification. If a system contains software, some accepted methods on quantification of software reliability exist, but none of them is generally applicable, as we will show.We propose a model bringing software into the quantitative risk assessment domain by introducing failure of software modules (with their probabilities) as basic events in a fault tree. The method is known as 'TOPAAS' (Task-Oriented Probability of Abnormalities Analysis for Software). TOPAAS is a factor model allowing the quantification of the basic 'software' events in fault tree analyses. In this paper, we argue that this is the best approach currently available to industry.Task-Oriented Probability of Abnormalities Analysis for Software is a practical model by design and is currently put to field testing in risk assessments of programmable electronic safety-related systems in tunnels and control systems of movable storm surge barriers in the Netherlands.The TOPAAS model is constructed to incorporate detailed fields of knowledge and to provide focus toward reliability quantification in the form of a probability measure of mission failure. Our development also provides context for further in-depth research.

Economic optimization of coastal flood defence systems including storm surge barrier closure reliability

“…Other unavailability of electro-mechanical equipment is related to the hydraulic conditions at the closure, which are not necessarily related to those at the peak of the storm. Software reliability is related to the complexity of the software, the production process, quality of software engineers and quality of testing (Van Manen et al, 2015). Reliability of human operation depends on staff and training quality F I G U R E 2 Schematic overview of a storm surge barrier flood protection system with one polder considered for the economic optimization model.…”