- The "event occurrence time" - the time that the event happened in the reality
- The "event detection time" - the time that the event was emitted / signalled / detected by the event processing system (typically a single time-point).
- The "event valid time" - the time-interval in which the event may effect the event processing system - typically starts at the time it starts to effecting the processing, and ends at the time it stops effecting the processing. This is less obvious then the other two, but important for some types of processing.
In some cases the order of events do not matter, however, when it matters - e.g. a pattern is depends on the fact that event e2 occurs after event e1 (such as: the order of the events "printer is offline" and "printer is online" of course matters, since it indicates whether the problem has been resolved or is still there. The order in this case is of course according to the "event occurrence time" (note that if the event occurrence time is an interval, there may not be a total order, but interval relations).
This is only a start of the temporal saga in event processing, there are many more questions that I'll try to include in future blogs:
- What happens if events are getting out of order ? (short and long delays) ?
- What is the "occurrence time" and "detection time" of derived events ?
- What is retrospective event processing, and how it fits in ?
- What is temporal context and how it relates to time window ?
More on all of these - later.