Transactional vs. Reactive systems is not a good way to think about it IMHO. A "Reactive system" is basically a "Transactional system" that in addition takes a

Transactional vs. Reactive systems is not a good way to think about it IMHO. A "Reactive system" is basically a "Transactional system" that in addition takes a system state as input and returns a (updated) system state as output: reactive_system : (State * Input) -> (State * Output) Which makes it identical (from a formal point of view) to a "Transactional system".