Monitoring hierarchical agent-based simulation traces

Due to their internal complexity, agent-based simulations are rarely amenable to conventional formal verification. With its focus on individual traces, runtime verification represents an interesting alternative for correctness assessment. Here, execution traces produced by the running system are observed by a monitor and checked for correctness on-the-fly. If the truth or falsity of a given property cannot be determined at time t, then the monitor creates an obligation that the current trace needs to satisfy at time t + 1 in order for the whole property to become true. With different observational levels, traces produced by agent-based simulations have an inherently hierarchical nature which complicates the structure and manipulation of obligations significantly. However, it turns out that this problem is general enough to be dealt with in an abstract, language-independent way. In this paper, we provide a general framework for the monitoring of hierarchical traces. It introduces different types of obligations and appropriate manipulation procedures along with minimal requirements that a property specification language needs to satisfy in order to be monitorable. We provide a full formalisation of the framework and an example implementation of a subset in Haskell.