On the Expressiveness of Parameterized Finite-state Runtime Monitors On the Expressiveness of Parameterized Finite-state Runtime Monitors?

Many contemporary runtime-verification tools instrument a program under test with finite-state runtime monitors that can be parameterized through variable-to-object bindings. Often, such tools provide a specification formalism that is some form of syntactic extension to an aspect-oriented programming language. The tools then transform monitor specifications into aspects that bind the monitors’ parameters through pointcuts. In this work we show that the availability of certain, well-selected pointcuts and the variable bindings that these pointcuts expose can greatly enhance the expressive power of finite-state monitoring formalisms, often going clearly beyond the expressiveness of regular languages. Formally, this e↵ect can be explained by a correspondence between finite-state machines and Weak Monadic Second-Order Logic (MSO). For this logic it is known that it can exactly express the regular languages when combined with a successor relation over string positions—adding other relations may increase its expressiveness. In the conceptual framework of this logic, such adjunct relations correspond directly to primitive pointcuts in the underlying aspect language.