A Scala DSL for Rete-based Runtime Verification

Abstract. Runtime verification (RV) consists in part of checking execution traces against formalized specifications. Several systems have emerged, most of which support specification notations based on state machines, regular expressions, temporal logic, or grammars. The field of Artificial Intelligence (AI) has for an even longer period of time studied rule-based production systems, which at a closer look appear to be relevant for RV, although seemingly focused on slightly different application domains, such as for example business processes and expert systems. The core algorithm in many of these systems is the Rete algorithm. We have implemented a Rete-based runtime verification system, named LogFire (originally intended for offline log analysis but also applicable to online analysis), as an internal DSL in the Scala programming language, using Scala’s support for defining DSLs. This combination appears attractive from a practical point of view. Our contribution is in part conceptual in arguing that such rule-based frameworks originating from AI may be suited for RV.

ITL Monitor: Compositional Runtime Analysis with Interval Temporal Logic

Runtime verification has gained significant interest in recent years. It is a process in which the execution trace of a program is analysed while it is running. A popular language for specifying temporal requirements for runtime verification is Linear Temporal Logic (LTL), which is excellent for expressing properties such as safety and liveness. Another formalism that is used is Interval Temporal Logic (ITL). This logic has constructs for specifying the behaviour of programs that can be decomposed into subintervals of activity. Traditionally, only a restricted subset of ITL has been used for runtime verification due to the limitations imposed by making the subset executable. In this thesis an alternative restriction of ITL was considered as the basis for constructing a library of runtime verification monitors (ITL-Monitor). The thesis introduces a new first-occurrence operator (|>) into ITL and explores its properties. This operator is the basis of the translation from runtime monitors to their corresponding ITL formulae. ITL-Monitor is then introduced formally, and the algebraic properties of its operators are analysed. An implementation of ITL-Monitor is given, based upon the construction of a Domain Specific Language using Scala. The architecture of the underlying system comprises a network of concurrent actors built on top of Akka - an industrial strength distributed actor framework. A number of example systems are constructed to evaluate ITL-Monitor's performance against alternative verification tools. ITL-Monitor is also subjected to a simulation that generates a very large quantity of state data. The monitors were observed to deliver consistent performance across execution traces of up to a million states, and to verify subintervals of up to 300 states against ITL formulae with evaluation complexity of O(n^3)