System engineering is the art and science of creating effective systems, using whole system, whole life principles. - Derek Hitchins

Architecture is defined as the art and science of creating buildings. Systems engineering may be similarly defined as the art and science of creating systems.

For continued system cohesion, the mean rate of system adaptation must equal or exceed the mean rate of change of environment.

A system is an open set of complementary, interacting parts, with properties, capabilities and behaviours of the set emerging both from the parts and from their interactions to synthesize a unified whole.