Events and Messages

In general, we mean by any concept nothing more than a set of operations; the concept is synonymous with a corresponding set of operations.

-- Percy Bridgman, The Logic of Modern Physics, paper

The conversation started to become a little confusing when the guy at the end of the table mentioned that as soon as I have sent the event and when the guy next to me countered with that the event contains the message I need to process.

It's not uncommon to use a mix of terminologies that makes little or no sense when taking a deeper look at them. Events and messages are two of the prime candidates for confusion and misunderstandings in IT discussions. More than often messages and events are talked about in an interchangeable way with consequences – usually bad ones - reaching all the way from design meetings to the bits and bytes stored on the disk platters.

Let's take a look at a reasonable view of what events and messages could and should mean. But, before looking at it lets lay down the usual ground rule for what to expect when looking at concepts within IT: everything is relative – nothing is absolute!

The idea of what the meaning of the word event is could be pretty simple. An event is simply a happening which has a before and an after but not a during. It sounds kind of abstract but it makes a lot of sense. And by the way, what else could it really mean? So, since the idea makes sense and is simple enough I'll stick to it.

Now, what about the historical event when the Visigoths sacked Rome in 410 AD? Clearly there was a before, an after and a during the sacking of the city. Now one might say that something is definitely wrong here - an event having something happening during the event goes against what I mentioned previously. It's exactly the one property an event should not have.

Intuitively it's obvious that sacking of Rome didn't happen instantaneously. It must have taken some time to plunder and demolish a large city even though the Visigoths were probably pretty good fighters. This is where the idea of a relative notion comes into play. That is, to make sense of a concept the meaning of the concept must be relative to something else. In this case it seems to be sensible to relate the meaning of the word event to time ticks. Or more precisely, to classify something as an event I must relate the event to the length of the time ticks through which I view the world.

If I was a historian I might view the history of the world using a clock ticking a year at a time. Doing so, there is a before a year and an after a year but not a during a year. Now I can surely say that the sacking of Rome in 410AD was an historical event.

The obvious question now is: How should I choose the length of my clock ticks? The best answer I have come up with is to choose it in such a way that it helps me focus on what is important in the problems that I'm trying to solve. After all, at the end that's all that matters.

Now, is a message an event? By the definition above it is not. A message would only make sense in a context where I have time to read the message so I would have to set my clock ticks in such a way that there is a time period during which the message exists. A message is therefore by its very nature not an event. In the same way, an event is neither a message.

Am I not nit-picking and dissecting something obvious here? Event or message, does it really matter what I call something? Sometimes it may not matter much but at other times it turns out to be crucial to use consistent terminology when more than a few people are involved in a project. Myself, I believe that using the right terminology is always preferable.

By the way, the sacking of Rome in 407 AD could be classified in a number of ways. Right of the bat, depending on the purpose and the time ticks I use, I could say it was an event, a process or an entity.