Formalization and Detection of Events Using Interval-Based Semantics

Active databases utilize Event-Condition-Action rules to provide active capability to the underlying system. An event was initially defined to be an instantaneous, atomic occurrence of interest and the time of occurrence of the last event in an event expression was used as the time of occurrence for an entire event expression (detection-based semantics), rather than the interval over which an event expression occurs (interval-based semantics). This introduces semantic discrepancy for some operators when they are composed more than once. Currently, all active databases detect events using the detection-based semantics rather than the interval-based semantics. SnoopIB is an interval-based event specification language developed for expressing primitive and composite events that are part of active rules. Algorithms for event detection using interval-based semantics pose some challenges, as not all events are known (especially their starting points). In this paper, we address the following: 1) briefly explain the need for interval-based semantics, 2) formalization of events accumulated over a semantic window and 3) how diversified events (e.g., sliding window, accumulated) are detected using interval-based semantics in the context of Sentinel – an active object oriented database.