Assessing the Usefulness of Assurance Cases: An Experience with the CERN Large Hadron Collider
Abstract
Assurance cases are structured arguments designed to show that a system functions properly in its operational environment. They are mandated by safety standards and are largely used in industry; however, they are typically proprietary and not publicly available. Therefore, the benefits of assurance case development are usually not rigorously documented, measured, or assessed. In this paper, we present an assurance case for the CERN Large Hadron Collider (LHC) Machine Protection System (MPS). We used open-source documentation for its creation and used the eliminative argumentation, methodology for assurance case development. The development involved four authors with considerable experience in assurance case development, three of whom work for Critical System Labs, a small enterprise specializing in assurance cases. Our experience shows that (a) the cost and time required to develop our assurance case is negligible compared to the effort needed to develop the system, and (b) eliminative argumentation helped identify 10 defeaters not detailed in the documentation used for creation of the assurance case. In this paper, we describe our experience and findings, and also discuss how the LHC assurance case helped accurately identify Key Performance Indicators for the MPS.