[pphysch]

May be referring to the common 3 layer architectures (see Fowler's PoEAA) which map closely to ECS:

Top layer is for "frontend", whatever that means for the product (UI, sound, simulation, etc.), the stuff with side effects. "Systems".

Middle layer is purely functional, for business/domain logic AKA utility functions. The most liquid layer, but should not be confused as trivial.

Bottom layer is where state (or a way to access & modify it) lives. Data access layer, component layer, etc.

[tompazourek]

I don't think they really map that closely... But you might be right. Thanks.