The concept of a function is central both to biology and to technology. But there is an intricate debate how functions as well as related entities like dispositions and roles are to be represented in top level ontologies and how they are to be related. We review important philosophical accounts and ontological models for functions and roles and discuss three models for the relation of functions and dispositions. We conclude that mainly because of the need to account for malfunctioning, functions (...) should not be treated as a subtype of dispositions, but as their sibling category. (shrink)