The Command Event Fallacy In The Process Level EventStorming Sessions

During the analysis of a certain process, you might end up with just one command that leads only to one event. It has happened to me during our first Process Level sessions. We did find commands to the events that we’ve spotted in the Big Picture session and it felt just right.

Is It Really That Simple?

There’s a catch though. You might end up with a model of the system that looks just like a CRUD. Is the whole system just a CRUD? Hmm… In most cases probably not. In my case, it was the same. We just didn’t analyze well enough. We didn’t dig too much into the consequences of the commands.

The Aha Moment

For me, it clicked when I saw an experienced facilitator driving the session. It was a pivotal experience. I immediately noticed that what we did is not good enough. We revisited it.
So if you notice such a model, either play the silly person in the room and read it aloud or ask a question about other consequences of that command. What I really like to do when reading aloud is to stress that the event is the only reaction from the business. Even though sometimes it might sound stupid, it works.

But is it always wrong? Not necessarily. Sometimes it’s just CRUD. And that’s completely fine. Not the entire domain has to be complex, right? Sometimes we just save something, and in the effect, it’s saved. There are no other consequences.

Summary

In short, watch out for Command – Event (anti)pattern. Ask every question “Is the [event] only consequence of [command]”? Speaking it out loud might provoke a discussion of what else is happening or should happen. However, there might be nothing. Then don’t force it. It might be just CRUD. And that is absolutely fine.

There’s a short Order example in the EventStorming cheat sheet that I’ve prepared. You can find it here.