EVA: An event algebra supporting complex event specification
In applications such as digital libraries, stock tickers, traffic control, or supply chain management, composite events have been introduced to enable the capturing of rich situations. Composite events seem to follow common semantics. However, on closer inspection we observed that the evaluation semantics of events differs substantially from system to system. In this paper, we propose a parameterized event algebra that defines the detailed semantics of composite event operators. We introduce composite event operators that support explicit parameters for event selection and event consumption. These parameters define how to handle duplicates in both primitive and composite events. The event algebra EVA forms the foundation for a unifying reference language that allows for translation between arbitrary event composition languages using transformation rules. This translation, in turn, enables a mediator service that can federate heterogeneous event-based systems. Our approach supports the seamless integration of event-based applications and changing event sources without the need to redefine user profiles. The event algebra is exemplified in the domain of transportation logistics.