Resource-Predictable and Efficient Monitoring of Events

Abstract: We present a formally specified event specification language (Solicitor). Solicitor is suitable for real-time systems, since it results in resource-predictable and efficient event monitors. In event monitoring, event expressions defined in an event specification language control the monitoring by matching incoming streams of event occurrences against the event expressions. When an event expression has a complete set of matching event occurrences, the event type that this expression defines has occurred. Each event expression is specified by combining contributing event types with event operators such as sequence, conjunction, disjunction; contributing event types may be primitive, representing happenings of interest in a system, or composite, specified by event expressions.The formal specification of Solicitor is based on a formal schema that separates two important aspects of an event expression; these aspects are event operators and event contexts. The event operators aspect addresses the relative constraints between contributing event occurrences, whereas the event contexts aspect addresses the selection of event occurrences from an event stream with respect to event occurrences that are used or invalidated during event monitoring. The formal schema also contains an abstract model of event monitoring. Given this formal specification, we present realization issues of, a time complexity study of, as well as a proof of limited resource requirements of event monitoring.We propose an architecture for resource-predictable and efficient event monitoring. In particular, this architecture meets the requirements of realtime systems by defining how event monitoring and tasks are associated. A declarative way of specifying this association is proposed within our architecture. Moreover, an efficient memory management scheme for event composition is presented. This scheme meets the requirements of event monitoring in distributed systems. This architecture has been validated by implementing an executable component prototype that is part of the DeeDS prototype.The results of the time complexity study are validated by experiments. Our experiments corroborate the theory in terms of complexity classes of event composition in different event contexts. However, the experimental platform is not representative of operational real-time systems and, thus, the constants derived from our experiments cannot be used for such systems.