From BOWiki
Functional Item
In OF, functional items are special roles which appear in the realizatio nof functions. Note that usually there are more roles involved in the realization of a function than a single role given by the functional item. In a transport process, for example, in addition to the role "transporter" there is a "cargo" role, referring to that which is transported. Hence, the functional item singles out a particular role whose player is the entity having the function.
Goal
Functions are goal-oriented entities - specifying a function requires providing the goal it serves. The goal of the function is a state or part of the world - temporally extended or not - which is intended to be achieved by any realization of the function. In the case of transporting oxygen, the location of the oxygen at B is the goal. The goal specifies only the part of the world directly affected by the function. Often a goal is embedded in a wider context, called final state. A final state of a function contains the goal plus an environment for the goal, therefore making the goal more comprehensible.
Requirements
The requirements of the function contain all the necessary preconditions which must be met whenever the function is to be realized. For example, in case of the function "to transport oxygen from A to B", oxygen must exist at location A.
Function description according to OF:
