Tuesday, January 22, 2008

On The WHEN question - in event processing

In one of the previous postings I have talked about various notions of real-time, from the example of the human event processing that I have given yesterday, it seems that there is importance in some cases to react in "hard real-time", e.g. if we'll assume that instead of human drivers the cars will be driven by a computerized system, then this system will have a lot of hard real-time constraints, especially when related to safety, based on events that received from sensors about the environment. An inheritance from active databases is the distinction between "immidate action" and "deferred action", however these are inaccurate terms-

Immediate typically means:

  • As soon as possible based on best effort,

However sometimes it means :

  • Hard or soft real time constraints on the latency.

Deferred may mean:

  • As soon as possible after the end of some context (e.g. at the end of a time window)

But it may also means:

  • Exactly in 5:00PM, Anytime between 7:00 - 9:00 PM etc..

Indeed - not all events are processed immediately, the best example is an absent pattern based on time-out, in which the fact that the event did not happen is processed at the end of the time-out .

In some cases we also want to apply event patterns to historical event - which is known as "retrospective processing"; this will be discussed in another opportunity.

No comments: