A unified approach for specifying timing constraints and composite events in active real-time database systems

Abstract

In active database systems, events are used in ECA rules to specify the time to check the conditions of the rules. Composite events can be constructed in an intuitive way by applying event operators, such as and, or, sequence, etc., to primitive events. Where timing is important, these event operators may introduce ambiguity if there is no formal semantics defining the occurrence of the composite events. The authors propose a formalism to specify a wider range of composite events with formal semantics in the logic RTL which is especially amenable for specifying timing constraints in real-time systems. The use of RTL to define the formal semantics also allows us to exploit compilation methods which can be used to translate the enabling conditions of ECA rules into timing constraints. Thus the detection of composite events can be handled by monitoring the corresponding timing constraints, a subject which has been explored in their previous work. A prototype implementation of this approach, a Java package for composite event specification, compilation and detection, is discussed in the paper.