Function (glossary)

(1) A system outcomes which contribute to goals or objectives. To have a function, a system must be able to provide the outcome through two or more different combinations of elemental behavior .

(2) An action, a task, or an activity performed to achieve a desired outcome.

(3) A broad work area encompassing multiple related disciplines (e.g., Engineering, Finance, Human Resources, etc.).

(4) A function is defined by the transformation of input flows to output flows, with defined performance.

Source

(1) Ackoff, R.L. 1971. Towards a System of Systems Concepts, Management Science, Vol.17 No. 11, USA.

(2) Hitchins, D. (2007) Systems Engineering: A 21st Century Systems Methodology: Wiley

Discussion

(1) is the system science definition. All systems have behavior, but to be able to function in a certain way they must have a certain richness of behavior. For example, fight, flight or hide are behaviors; while response to external threats is a function.

(2) is the more traditional Systems Engineering definition, in which functions are identified top down based on needs and then decomposed and allocated to lower level system.

(3) is a HW/SW or human system component definition, describing a function which can be performed by a single part of the system with identified performance.

(4) is a management definiton, describing how similar functions are collected in organizational units.