Sequencing in the Run-Time Event Calculus

Periklis Mantenoglou, Alexander Artikis

Abstract: Composite event recognition (CER) systems detect instances of composite activities over streams of timestamped events. A fundamental operator for CER is ‘sequencing’, expressing that two activities take place one after the other. There is no consensus on a universal definition for sequencing. We provide a set of required properties for a sequencing operator for CER, i.e., an interval-based semantics, required for durative activities, and associativity, required to express activity hierarchies. We propose a sequencing operator that satisfies all requirements, as opposed to the ones in the literature, and we implement our operator in the CER engine RTEC. We compare our operator both theoretically and empirically with state-of-the-art approaches, demonstrating its benefits and limitations.