That’s a very good question, because sequencing tends to be the place where implementations vary the most. Usually there will be some way to sort systems into

That’s a very good question, because sequencing tends to be the place where implementations vary the most. Usually there will be some way to sort systems into steps and define the order of those steps. Some require you to hardcode the order, others define constraints like “after input” or “before physics” and attempt to solve those constraints, and some let you define groups that can run together and you define the order of the groups. Explicit signaling is not typically built in, but you may be able to implement it yourself if desired. In environments with an expressive type system, most tend to favor the constraints model. Otherwise ordering tends toward the hardcoded approach, typically implicitly in registration order. As to managing what systems are responsible for updating a given component’s state, that tends to be left to the game developer. Sometimes there is a concept of events and if it’s not obvious who should mutate something then systems that want to mutate will send events that later systems can consume. For instance an input system and an AI system might both send a Move(entity, direction) event that a later system validates and applies. And because it’s cute to do so, often times those events will be implemented as components themselves, with convenience wrappers to make it feel more natural to end user developers. This can come in handy for networked games and debugging in editor. You could also use it in game, such as displaying a unit’s next planned move in a turn-based game.