Conjunction, sequence, and interval relations in event stream processing

The conjunction operator can be augmented with temporal constraints to define an arbitrary pattern of events in event stream processing (ESP). However, using temporal constraints to specify patterns can be complex. This research has defined an operator hierarchy, where the top of the hierarchy defines the conjunction operator and the leaves of the hierarchy define more specific semantics associated with a sequence of events. The use of the specialized operators simplifies pattern expression and make the sequence semantics clear. Furthermore, in an experimental study, patterns using operators from the hierarchy outperform patterns expressed using the conjunction operator with temporal constraints in run time performance, further validating the usefulness of the operator hierarchy.