In fact, it is possible to realize the same function using different physical processes, and one process can be the carrier of multiple functions (Adam Maria Gadomski, 1987). For example, the main function of a clock, the presentation of time, can be realized by different physical processes, including atomic, electronic, and mechanical processes.
In many cases, this concept is also used in a metaphoric sense, for example, by attributing a goal to the natural selection processes.
If we change the use of an object, it may change dramatically functions without changing any of its own physical properties.
In the lifecycle of engineering projects, there are usually distinguished subsequently: Requirements and Functional specification documents. The Requirements usually specifies the goal attributes of the requested system, and "The Functional Specification defines what the functionality will be, but not how that functionality will be implemented. "(Functional Specification from the EPRI Institute Portal), and the next Design Specification document describes physical or software processes and systems which realize (are carriers of) the requested functions.
There are distinguished internal and external system functions. From an external observer perspective, the services offered by an engineering system to its users are the system external functions. The functions which are necessary for their realization are called system internal functions.
From the systemic perspective, functions are divided according to the main goals of engineering systems (Morten Lind), they are:
This taxonomy was applied in Multilevel Flow Modeling (MFM) for the graphical representation of goals and functions of complex nuclear plants.