Nowadays events are omnipresent and exchanged as messages over networks. Characteristic for applications involving advanced (or complex) event processing is the need to (1) utilize data contained in the events, (2) detect patterns made up of multiple events (so-called composite events), (3) reason about temporal and causal relationships of events, (4) accumulate events for negation and data aggregation.

This article describes a high-level language approach for expressing queries to events. Its foundations are: embedding of a query language for XML and other Web data formats, support for rule-based reasoning, and a complete coverage of the four dimensions mentioned above.