Abstract. A dramatic increase of event monitoring capabilities by wireless sensors requires new, more sophisticated, event correlation over time and space. This new paradigm implies composition of events in ubiquitous computing environments and event Correlation will be a multi-step operation from event sources to final subscribers, combining information collected by wireless devices into higher level information or knowledge. We define generic composite event semantics, which extend traditional event composition with data aggregation in wireless sensor networks (WSNs). This work bridges data aggregation in WSNs with event correlation services over distributed systems. We use interval-based semantics for event detection, defining precisely complex timing constraints.