TOPAAS model

The Dutch Directorate of Infrastructure and Watermanagement performs probabilistic maintenance on all main surge barriers, locking systems and similar objects. Risk analysis plays a key role in modelling software failure, controlling test intervals, time to repair and deployment of improvements.

In cooperation with several companies and universities (DNV, Movares, TU Eindhoven, CGI en Intermedion) Refis developed a method to model software failure in a failure tree as well as a way to determine failure probability of software.

This method is called TOPAAS: Task Oriented Probability of Abnormalities Analysis for Software. It has become the default method for reliability analysis for several departments within the directorate.

Main principle of TOPAAS is that software will fail unless measures are taken to prevent that. Options to reduce failure probability for instance are application of IEC 61508, use of a  certified compiler and traceability of requirements down to test scripts. TOPAAS is an expert model in which 15 aspects of failure probability reduction are described and quantified. Read more on TOPAAS under papers and presentations or download the manual.