Function propagation through nested systems

Concepts of function are central to design but statements about a device's functions can be interpreted in different ways. This raises problems for researchers trying to clarify the foundations of design theory and for those developing design support-tools that can represent and reason about function. By showing how functions relate systems to their sub-systems and super-systems, this article illustrates some limitations of existing function terminology and some problems with existing function statements. To address these issues, a system-relative function terminology is introduced. This is used to demonstrate that systems function not only with respect to their most local super-system, but also with respect to their more global super-systems.

► Functioning objects are conceptualised as operating in multiple layers of sub-systems and super-systems (nested systems).
► Systems are shown to perform functions with respect to multiple super-systems (function propagation).
► An apparent conflict between competing perspectives on function propagation is resolved.