Thursday, December 18, 2008

"complex event" and "derived event" - are they synonyms ?

Israel is a small country, and its commercial TV stations just recently discovered the "reality" programs, this week was the final episode of a reality program called "big brother" in which a bunch of people are closed in a house (the one seen in the picture) for 3.5 months (those who survive until the end) doing nothing, without any connection to the outside world, and with cameras everywhere, there was a dedicated TV channel watching them 24 hours, and twice a week - TV show in prime time. This reality program drove the entire country crazy -- got unprecedented rating, and became the main discussion issue among people, today I went to the coffee room to take some coffee and have seen around 10 people there spending their time in a heated discussion around this TV program. Interestingly, in the night of the final, a group of people from the culture and artist community made a big demonstration against the TV channels that spend their production money on realities, and drop drama series -- I personally agree with them.
BTW -- event processing can be used to serve as a "big brother" and trace people's activities, but I'll blog about it another time.

I would like to answer the question of Hans Glide about my previous posting -- the question has been -- in the illustration (below) it is seen that "complex events" is not a subset of "derived events" meaning that there are complex events that are not "derived events" - is it true?

The answer is: indeed - "complex events" intersects "derived event" but there are derived events which are not complex events and complex events which are not derived events.

The first case is easy: enriched event is a derived event but it is not a complex event.
What about the other direction ? - well, getting back to what "derived event" is -- this is an event that is created by some "event processing agent" as a result of some event processing function. If an event is a raw event it is not derived event. However, there are in the universe
"raw complex events", not all complex events are derived by software artifacts. For example: Since David Luckham is the copywriter of the term "complex event", I'll use two of his favorite examples:


Economic Crisis

(David referred to the one started in 1929, but our generation also won one of these)

The "economic crisis" is a complex event -- it is certainly an event, and it is aggregation of other events, but this aggregation is not created by software, the raw event is already complex; likewise the "tsunami".

More - later.


Hans said...

I sometimes forget that these concepts apply to the real world as well as its representation in computers. I wonder if, in the computer world, we will see complex events that are not derived events.

I also wonder, what are the fields in an "economic crisis" event? :-)

Now if a bunch of events, some of which are derived and some not, together indicate a complex event, but without any derivation needed to form the complex event. Is that a derived complex event or not? Or maybe this is too much thought put into the topic.

Opher Etzion said...

Hi Hans - I will buy your last sentence -- "too much though put into the topic", since I believe that the concepts of derived events vs. raw event, and composite event vs. atomic event are in practice more useful than the concept of complex event; "economic crisis" is in fact an event that consists of collection of other events, so each of these events has its own attributes, I guess.

stay well,


henkdevries said...

Hi Opher,

I agree that "real-world" events can be complex by nature. In fact, I suspect that the real problem is finding a natural event that is truly simple (ie., atomic). I cannot think of any such event, because events can always be seen as being caused by several other events.

Take the examples from the EPTS glossary:

* A financial trade
The trade consists of two parts: stocks changing hands, and a certain amount of money changing hands. Both are events. In addition, a fee is going to the broker, etc. We group the events in our mind under the convenient term "trade".

* An airplane lands
What is a landing really? When the plane touches the ground? What if it bumps back into the air? Has it landed already when only one of its wheels have touched the ground, and the other is still in the air? Or does the plane need to stop? Because if it touches the ground and then crashes, we tend to say that the landing has failed..

These discussions about events v. derived events v. complex events suggest that there is something to gain by making distinctions between them (otherwise the discussion would be pointless). But I fear that any distinction will remain debatable.

Opher Etzion said...

Hi Henk -- the question if event is "raw" or "derived" is always relative-- it can be derived in one system and raw to another system. It does not necessarily impact the actual processing.