Saturday morning at home, after busy week and one resting day (our weekend is Friday and Saturday, tomorrow - Sunday, is again long and busy working day...) I am back in the Blogland.
Today I am in reactive mood, so will join a discussion thread that started by James Taylor who seems to have discovered that "event rules" and "decision rules" are not the same. Since this has been a reaction to a previous posting by Marco Siero, Marco actually agrees with him, saying that event rules and decision rules are not the same - saying that the "event rules" are in fact activation rules - saying WHEN a decision is needed. If they both agree then the thread of discussion can end.. -- nevertheless, I have some comments to this discussion:
1. The word "rules" is overloaded - there are many types of rules. Some rules deal with obtaining more facts (if the rules are based on logic it is called inference, and if the rules are based on data models it is called derivation), some with activating actions. Moreover, there are rules which are assertions about what is allowed and what is not (constraints) which are none of the above.
2. People have used the term "rules" to denote -- detect a pattern in events --- due to several reasons, one of them seems that rule has been the most closely known term that they could anchor at.
3. Today, when "event processing" is known by its own right, the use of term rules, when it is not needed is just confusing, and it is better to use the correct terms for event processing types.
4. I personally used the term "rules" for several years, but in the last three years have avoided doing it. It is difficult to get people change terminology, but sometimes it is required.
This, however, was just a comment on the term "rule", but let's get to the more interesting part -- as the title of the posting hints -- relationships between decisions and event processing.
The active database people have coined the term "active rule" which is also known as ECA rule, following its parts (event-condition-action). One can look at event processing network as an extension of ECA, in the sense that there is an entire processing done to get to the event that we actually want to react to, a raw event can be filtered, translated, aggregated, enriched, and
combined with other events that satisfy a certain pattern -- at then the event at the edge of the network (AKA situation) is the one that triggers the action.
The question whether an event processing application is doing decision or just notification that decision is needed, is not dependent on the event processing part - but on the type of action, if the action is notification -- notify somebody that the situation has been detected, I guess that it is what Marco meant in "activation rules", however, if the action is an automatic action (or several possible automatic actions based on conditions), then the result of the event processing is certainly a decision. There are cases in which the event processing ends in notification, e.g. most cases of BAM, and there are cases in which event processing ends in automated actions, e.g. send order to renew inventory, block a certain financial transaction and many other examples.
It also should be noted that the process of "event processing" may include decisions about the detection process itself -- examples: diagnosis, fraud detection - require application of decision components in order to determine what is the situation that occurred, which is also manifests itself in the decision.
James Taylor makes more interesting assertion: Event rules are not the same as the rules behind business decisions, even if the same language can be used to express both. One is tied to the events and the event handling system, one is not. I am not sure what is "tied" to the events, as said, the "action" takes part outside the event processing network, and it certainly can be a case of hybrid system, in which an event processing network detects what happened and the action attached to it is a "business rule" that decides what the reaction should be based on the situation. More- Later.