Comments on: In the names of CEP and BPM http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/ systems that know and understand and think and learn Fri, 21 Nov 2008 10:38:15 +0000 http://wordpress.org/?v=2.3.1 By: paul@haleyAI.com http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-53 paul@haleyAI.com Mon, 17 Mar 2008 16:18:34 +0000 http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-53 You are more than welcome. My appeal is to avoid deep philosophy and focus on common sense and consensus. If the common person does not agree with our definition of event, we are stuck. We need a definition of event that is simple, not exact. A generality. But true. If we cannot say "yes" to "do events happen?", we are lost. You are more than welcome. My appeal is to avoid deep philosophy and focus on common sense and consensus. If the common person does not agree with our definition of event, we are stuck. We need a definition of event that is simple, not exact. A generality. But true. If we cannot say “yes” to “do events happen?”, we are lost.

]]> By: snshor http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-52 snshor Mon, 17 Mar 2008 15:52:20 +0000 http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-52 Paul, Thanks for your reply, To clarify, my "atomic(and constant)" rather meant "immutable". "Instantaneous" is probably a logical consequence of immutability. That's the problem with semantics - if even so called "experts" can not agree on the meaning of the word - then there is a trouble. For example, I do not see the need of having "event with a duration" instead of "activity", is it just a matter of taste? I understand, that we need to tolerate ambiguity on business vocabulary level, but on underlying semantic level there should be a clear separation. And coming from Shlaer-Mellor perspective (at least from my understanding of it) events ARE notifications, I would also add that Events are the major source of process state change. I don't know is it implementation specific or not, but the best way to settle this is to analyze several use cases and see if there is other semantic to Event, if Activity is made disjoint from Event. Too broad definition can be confusing, we can say that "key pressed" is an Event and Business Rules Forum 2007 was an Yearly Event - but do they really have a lot in common? I understand your assertion that few events "actually have zero duration", but this is only true if we accept the broader definition of Event, otherwise we do not have to associate duration with Event at all. Point in time is a slippery concept, for example you receive two notifications about two events 8-)) that were generated on two different computers and the first one has a timestamp that is 2 sec earlier than the second one. Can you reliably state that the first event occured earlier? I'd say - no, and this is an intrinsic property of any Event pair form different sources in a real-world application. Will the fact that you received the former after the latter affect the conclusion? I say - no, there could be network(delivery) delay, etc. To keep the interaction consistent, we have to rely only on the "right" order of events from the single source (which is also takes an effort to guarantee). For example, if we had this discussion over email, and the system would not deliver emails from me in the order they were written, it would have much less sense, then it (hopefully) does now Paul,

Thanks for your reply,

To clarify, my “atomic(and constant)” rather meant “immutable”. “Instantaneous” is probably a logical consequence of immutability.

That’s the problem with semantics - if even so called “experts” can not agree on the meaning of the word - then there is a trouble. For example, I do not see the need of having “event with a duration” instead of “activity”, is it just a matter of taste?
I understand, that we need to tolerate ambiguity on business vocabulary level, but on underlying semantic level there should be a clear separation. And coming from Shlaer-Mellor perspective (at least from my understanding of it) events ARE notifications,
I would also add that Events are the major source of process state change.

I don’t know is it implementation specific or not, but the best way to settle this is to analyze several use cases and see if there is other semantic to Event, if Activity is made disjoint from Event.
Too broad definition can be confusing, we can say that “key pressed” is an Event and Business Rules Forum 2007 was an Yearly Event - but do they really have a lot in common?

I understand your assertion that few events “actually have zero duration”, but this is only true if we accept the broader definition of Event, otherwise we do not have to associate duration with Event at all.

Point in time is a slippery concept, for example you receive two notifications about two events 8-)) that were generated on two different computers and the first one has a timestamp that is 2 sec earlier than the second one.
Can you reliably state that the first event occured earlier? I’d say - no, and this is an intrinsic property of any Event pair form different sources in a real-world application.

Will the fact that you received the former after the latter affect the conclusion? I say - no, there could be network(delivery) delay, etc. To keep the interaction consistent,
we have to rely only on the “right” order of events from the single source (which is also takes an effort to guarantee).
For example, if we had this discussion over email, and the system would not deliver emails from me in the order they were written, it would have much less sense, then it (hopefully) does now

]]> By: paul@haleyAI.com http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-51 paul@haleyAI.com Mon, 17 Mar 2008 12:45:59 +0000 http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-51 Interesting "system of coordinates" comment, but it seems stronger with respect to your point in time comments. That we can understand each other implies that we share some ontology which defines an event and a point in time. We may have different word senses or refinements, but it is the commonalities that are critical. Perhaps your "atomic" is my "instantaneous" and your "activity" is an event with a duration (i.e., another way of refering to a process). Last 4th of July's picnic cannot be interrupted, but few events actually have zero duration and there are processes that cannot (reasonably) be interrupted. Isn't thinking about events as notifications an implementation rather than a semantic perspective? On the points in time, you are more consistent and complete with respect to relativity, but natural man would not care. BTW, I did not say that the GMT for a point it time was necessarily specified, only that it existed. Adding something beyond timezones, such as frames of reference, has merit in physics or the distant future, perhaps. I hope others feel motivated to comment on this. It is clearly a critical need in multiple areas spanning the semantic web, CEP, BPM, ... But we have to be careful to tolerate ambiguity and, therefore, focus on generality, without introducing jargon. If we make "event" an overly precise concept, we will never reach concensus and non-scientists will remain alienated and unengaged with our work. Rather than narrow the definition of an event, why not use adjectives (or other words) to be more precise when needed? Interesting “system of coordinates” comment, but it seems stronger with respect to your point in time comments. That we can understand each other implies that we share some ontology which defines an event and a point in time. We may have different word senses or refinements, but it is the commonalities that are critical.

Perhaps your “atomic” is my “instantaneous” and your “activity” is an event with a duration (i.e., another way of refering to a process). Last 4th of July’s picnic cannot be interrupted, but few events actually have zero duration and there are processes that cannot (reasonably) be interrupted. Isn’t thinking about events as notifications an implementation rather than a semantic perspective?

On the points in time, you are more consistent and complete with respect to relativity, but natural man would not care. BTW, I did not say that the GMT for a point it time was necessarily specified, only that it existed. Adding something beyond timezones, such as frames of reference, has merit in physics or the distant future, perhaps.

I hope others feel motivated to comment on this. It is clearly a critical need in multiple areas spanning the semantic web, CEP, BPM, … But we have to be careful to tolerate ambiguity and, therefore, focus on generality, without introducing jargon. If we make “event” an overly precise concept, we will never reach concensus and non-scientists will remain alienated and unengaged with our work. Rather than narrow the definition of an event, why not use adjectives (or other words) to be more precise when needed?

]]> By: snshor http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-50 snshor Mon, 17 Mar 2008 06:21:50 +0000 http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-50 IMHO, the best definition of Events and States had been done in the beautiful book by Sally Shlaer and Stephen Mellor "Object Life Cycles: Modeling the World In States". (I still don't understand why CEP vendors do not use their methodology - at least I could not find direct references to it). I do not agree with your statement that processes can be viewed as events - not in the same "system of coordinates" at least. Events are atomic (and constant) by nature and processes are stateful. You can not have both in the same model. So, 4th of July picnic is not an Event(I feel that English semantic of "school event" got mixed up;), but invitation to the picnic could be. I would rather categorize Picnic as an Activity (i.e something that has start and finish, can be interrupted, postponed or even canceled, may have observers etc.). So, in "my ontology", events do not occur - they are notifications about something that occurred - more or less like in Paul Vincent's post. And, on a side note, "a point in time" only makes sense if we use the same timer for all events, otherwise relying on this attribute may cause problems. Shlaer-Mellor methodology requires only that events from the same source were delivered in the order they were created, but makes no assumptions about events from different sources. IMHO, the best definition of Events and States had been done in the beautiful book by Sally Shlaer and Stephen Mellor “Object Life Cycles: Modeling the World In States”. (I still don’t understand why CEP vendors do not use their methodology - at least I could not find direct references to it). I do not agree with your statement that processes can be viewed as events - not in the same “system of coordinates” at least. Events are atomic (and constant) by nature and processes are stateful. You can not have both in the same model. So, 4th of July picnic is not an Event(I feel that English semantic of “school event” got mixed up;), but invitation to the picnic could be. I would rather categorize Picnic as an Activity (i.e something that has start and finish, can be interrupted, postponed or even canceled, may have observers etc.). So, in “my ontology”, events do not occur - they are notifications about something that occurred - more or less like in Paul Vincent’s post. And, on a side note, “a point in time” only makes sense if we use the same timer for all events, otherwise relying on this attribute may cause problems. Shlaer-Mellor methodology requires only that events from the same source were delivered in the order they were created, but makes no assumptions about events from different sources.

]]> By: Paul Vincent http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-48 Paul Vincent Sat, 15 Mar 2008 16:49:10 +0000 http://haleyai.com/wordpress/2008/03/14/in-the-names-of-cep-and-bpm/#comment-48 Thanks Paul, interesting question. A similar topic was discussed in the Business Architecture working group at OMG last week. One of the speakers presented: Business Entity = data entity + data model + lifecycle state model Business Process Model = set of communicating business entities Business Service = state transition in business entity in its lifecycle Normally, of course, Event = observation of state or state change So Event and Process are certainly related... Thanks Paul, interesting question.

A similar topic was discussed in the Business Architecture working group at OMG last week. One of the speakers presented:
Business Entity = data entity + data model + lifecycle state model
Business Process Model = set of communicating business entities
Business Service = state transition in business entity in its lifecycle

Normally, of course,
Event = observation of state or state change

So Event and Process are certainly related…

]]>