SnoopIB: Interval-Based Event Specification and Detection for Active Databases

Snoop is an event specification language developed for expressing primitive and composite events that are part of Event-Condition-Action (or ECA) rules. In Snoop, an event was defined to be an instantaneous, atomic (happens completely or not at all) occurrence of interest and the time of occurrence of the last event in an event expression was used as the time of occurrence for the entire event expression. The above detection-based semantics does not recognize multiple compositions of some operators – especially Sequence – in the intended way. In order to recognize all event operators, in all contexts, in the intended way, operator semantics need to include start time as well as end time for an event expression (i.e., interval-based semantics). In this paper, we formalize Snoop Interval-Based (SnoopIB), the occurrence of Snoop event operators and expressions using interval-based semantics. The algorithms for the detection of events using interval-based semantics introduce some challenges, as not all the events are known (especially their starting points).