Complex Event Processing and Event Stream Processing

In the most general sense, the term event refers to anything that happens in a system. For example:

• A password change

• A stock purchase

• A transfer of funds

You use IEP to process computerized representations of these events.

These events are generated and sent out by applications. The applications can be located within the enterprise service bus, or they can come from an external system that is connected to the enterprise service bus.

The term event stream refers to a continuous set of events. For example, an event stream could contain the password changes made by the users of a web-based application.

Processing an event stream can involve many types of activities. For example:

• You can examine a bounded portion of an event stream, such as all of the events that occurred in the last two minutes. This bounded portion is called a window.

• You can apply a function to a set of events. For example, you can determine the average price of a stock during the last three hours, with the calculation updated every five minutes.

• You can change the order of the events.

When you combine multiple events to create a higher level event, the result is called a complex event.

An architectural style in which software modules operate in response to the arrival of events is called event driven architecture.