[dagss]

At the boundaries are events. "User wanted to change time of meeting".

Once you have recorded events, figuring out what side-effects (often causing new events in other systems) should be triggered from the set of all events input into the system can be coded using whatever flavor of functional/relational/reactive programming.

I think the combination of event sourcing and functional programming, and databases that support this way of working better than today and doesn't have OOP as their main target audience, is the future. (And I absolutely don't mean Kafka. SQL comes at least closer; to efficiently work with events and implement functional business logic on top of events relations and structure is important.)