Physical artifacts and biological systems have been studied from a variety of perspectives in different disciplines. These entities show many common characteristics and are investigated using similar notions except for one important aspect: functionality. Notwithstanding many attempts, the search for a unified notion of functionality that could encompass both the functions attributed to natural objects, like biological organisms, as well as those attributed to designed objects, like artifacts, to date has remained an open challenge. Deepening an earlier characterization of engineering functions, this paper starts with an introduction to the notions of behavior and context, which become the basic blocks for the construction of a general framework for a unified definition of function. The approach distinguishes three types of functional contexts (systemic, user and design) and clarifies the role of goals in defining biological and artifact functions. Finally, it shows that the notion of systemic function, as detailed in the paper, succeeds in comprising both biological and artifact functions. The proposal is evaluated against a collection of desiderata and examples taken from the literature.
