Monitorability underpins the technique of runtime verification because it delineates what properties can be verified at runtime. Although many monitorability definitions exist, few are defined explicitly in terms of the operational guarantees provided by monitors, i.e. the computational entities carrying out the verification. We view monitorability as a spectrum, where the fewer guarantees that are required of monitors, the more properties become monitorable. Accordingly, we present a monitorability hierarchy based on this trade-off. For regular specifications, we give syntactic characterisations in Hennessy–Milner logic with recursion for its levels. Finally, we map existing monitorability definitions into our hierarchy. Hence, our work gives a unified framework that makes the operational assumptions and guarantees of each definition explicit. This provides a rigorous foundation that can inform design choices and correctness claims for runtime verification tools.

可监视性是运行时验证技术的基础，因为它描述了可以在运行时验证哪些属性。尽管存在许多可监视性定义，但很少明确定义根据监控器（即执行验证的计算实体）提供的操作保证。我们将可监视性视为一个频谱，其中监视器所需的担保越少，可监视的属性就越多。因此，我们提出了基于此权衡的可监视性层次结构。对于常规规范，我们使用Hennessy-Milner逻辑对其级别进行递归来给出语法表征。最后，我们将现有的可监视性定义映射到我们的层次结构中。因此，我们的工作提供了一个统一的框架，使每个定义的操作假设和保证都明确。这提供了一个严格的基础，可以为运行时验证工具提供设计选择和正确性声明。