At 05:41:07 on a winter morning, a message is published to a topic at a large hub airport. It is small, a few hundred bytes. It says that an inbound flight has been assigned a hold because a band of freezing fog has dropped visibility below minimums. The message does not know who will read it. That is the whole point of it.
By 05:41:08 it has reached fourteen subscribers. The flight information displays. The stand-planning system, which now has a conflict on the horizon. The baggage reconciliation system. A crew-management system that has just acquired a duty-time problem. A ground handler’s dispatch console. A catering scheduler. A passenger-notification engine. Some of these systems are twenty years old. Some were deployed last quarter. Not one of them was written with the others in mind. They subscribed to a topic, and the event found them.
This is how the best-run enterprises have worked for two decades. Exchanges, airports, banks, ports and factories moved from point-to-point integrations to events precisely so that adding a fifteenth subscriber would not require touching the other fourteen. We at Iesoft have spent most of our working lives inside that shift.
So here is the question that has been sitting with us for the last two years. What happens when some of those subscribers can reason?
The full piece walks four composite estates, at an airport, an exchange, a bank and a plant, and ends with when not to use an agent mesh at all.