Enforcement of Critical Observability in Modular Discrete-Event Systems

In safety-critical applications, the ability to distinguish between critical and noncritical states based on observations, known as critical observability (CO), is essential for ensuring reliability and security. We address the enforcement of CO in discrete-event systems (DES) through supervisory control. While a supremal CO sublanguage does not exist, we overcome this challenge by leveraging the concept of normality, proposing an algorithm to compute the least restrictive closed-loop system that is CO. We extend this approach to modular DES, showing how CO can be enforced locally to achieve global enforcement, thereby addressing scalability challenges. Finally, we integrate our framework with safety specifications, enabling the synthesis of supervisors that concurrently ensure both safety and CO.