Modern control systems in the maritime domain are increasingly controlled by software systems and become subject to updates and configuration changes during operation. Moreover, with the shift to autonomous vessels and cars, these software-based systems are taking on more and more safety-critical tasks, so the risks associated with system failures are increasing. Unlike before, it becomes necessary to verify the continuously adapting modules of a vehicle not only before deployment, but to establish continuous verification capabilities during all phases of the product lifecycle, from the design to the system in operation. Hence, in case of an update, deviations from the expected behavior can be automatically detected and relevant measures can be initiated. In this work, a contract-based verification framework is presented that includes automatable and formally analyzable behavioral descriptors in form of assumption-guarantee contracts for all phases of the software lifecycle to provide static and dynamic verification capabilities alongside a dynamically changing system composition. By utilizing contractually defined behavior descriptions, classic test procedures, such as simulations, are supplemented by a formally testable level that is applied to all phases of the update process. A conceptual-deductive methodology was chosen, building on the identified requirements to develop an overarching update framework that adds contractual descriptions to the traditional development case. Based on the presented framework, the verifiable modification of a safety-critical software system is demonstrated. The approach is evaluated using a maritime collision-avoidance system and the verification steps are evaluated along the update process. The framework offers a novel approach to complement existing test procedures by enabling formal impact analysis and incremental verification of updates.
July / 2021
Step-Up!CPS Software-Methoden und Technologien für Modulare Updates von Cyber-Physischen Systemen