Tim Bass
07-14-2008 11:17 PM
Often you will read or hear people talking about CEP and they will define a “complex event” as an event composed of other event-objects. Caution is advised, because a complex event is more than just a simple composite or aggregation of other events.
For example, in my earlier post
Modelling Situations for Event Processing, we illustrated modelling in CEP by looking at an example situation, “airplane collision”. This complex event is composed of many objects than are not event-objects. In fact, depending on how you define “event” most of the components of the complex event, “airplane collision” are not events at all, but other situations or sub-states of the objects under observation, in this case an aircraft.
For example, the direction an airplane is flying is not necessarily an “event” per se. Also, the amount of fuel on the aircraft at any given moment in time is not necessarily an “event” either. The same holds true for other components that comprise the object we are modelling. In fact, again depending on how you define “event”, most of the states of the components that are critical to processing a complex event are not events at all, they are simply object-states.
Complex events are generally composed of objects and the state of the complex event is defined by the objects in the complex event determined by the states of the components of the objects in the model.
Another way to view this key point is that CEP is characterised as predicting outcomes (states) based on the relationship between the objects in the model which are, in turn, composed of the states of various components of each of the objects.
So, in a nutshell, what is important to complex event processing is not just processing events, but processing the relative state of objects that comprise model of the complex event.
Furthermore, if you are someone who defines “event” as a simple a change of state, stay tuned in for another discussion in a future post; because the vast amount of state changes are not events per se; they are simply changes in states which may or may not have context and meaning in complex event processing.
Having said that, a complex event can be comprised of other events, including other complex events, that is why the notion of OO modelling and programming is very important in CEP.
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