Esper is an open-source Java-based software product for Complex event processing (CEP) and Event stream processing (ESP), that analyzes series of events for deriving conclusions from them.

This article includes a list of general references, but it lacks sufficient corresponding inline citations. (March 2015)

Esper extends the SQL-92 standard for its engine and enterprise framework, providing Aggregate function, Pattern matching, event windowing and joining. Esper implements Event-driven programming and event-driven architecture.

Esper was created in 2006 by EsperTech Inc. It offers a Domain-specific language for processing events called Event Processing Language (EPL). EPL is a Declarative programming language for analyzing time-based event data and detecting situations as they occur.

Esper is a Java-based application but has been ported to the C# programming language and is available for the .NET Framework under the name NEsper.

EsperTech Inc. provides Esper Enterprise Edition^[1] with enterprise-ability features.

This example^[2] illustrates a simple EPL query that outputs a row immediately when within a sliding window of 3 minutes the number of order events reaches 5 or more events.

select count(*) from OrderEvent#time(3 min) having count(*) >= 5

• Rapide (Stanford)
• StreamSQL: StreamSQL is a query language that extends SQL with the ability to process real-time data streams.

• Complex event processing (CEP) - A related technology for building and managing event-driven information systems.
• Data Stream Management System (DSMS) - A type of software system for managing and querying data streams
• Event correlation
• Event-driven architecture — (EDA) is a software architecture pattern promoting the production, detection, consumption of, and reaction to events.
• Event stream processing — (ESP) is a related technology that focuses on processing streams of related data.
• Operational intelligence — Both CEP and ESP are technologies that underpin operational intelligence.
• Pattern matching
• Real-time business intelligence — Business Intelligence is the application of knowledge derived from CEP systems
• Real-time computing — CEP systems are typically real-time systems
• Real time enterprise