Model element: Define the Thing's Function
A type of thing must have some function that it performs within a particular operating environment.
That is, it must use some inputs and produce some outputs.
Some outputs we can identify as useful (in some sense), while others may be categorized as waste, and others may be damaging or destructive.
Often, amounts of these inputs and outputs can be quantified.
In order to improve something, we generally want to minimize the inputs required, minimize the waste and damaging output, and maximize the useful output.