General Formal Ontology (GFO)
We understand a function to be an intentional entity, defined in
purely teleological terms by the specification of a goal, requirements
and a functional item. Functions are commonly ascribed by means of the
has-function relation to entities that, in some context, are the
realizations of the
goal, execute such realizations or are intended by a reliable agent to
do so. Functions are considered to be intentional entities and, hence,
they are not objective entities of the world, but agent-dependent
entities that primarily belong to the mental and social strata.
The pattern of the specification of a function , called a function
structure, is defined as a quadruple
, , where:
- denotes a set of labels of function ;
- denotes the requirements of function ;
Except for the label, these are called the function determinants, and
they determine a function. Labels are natural language expressions
naming the function. Most commonly, they are phrases in the form ``to do
something'', e.g. ``to transport goods''. The requirements of the function
set forth all the necessary preconditions that must be met whenever the
function will be realized. For example, in the case of the function
``to transport goods from to '', goods must be present at
Functions are goal oriented entities – specifying a function requires
providing the goal it serves. However, goals are not identified with
functions, as in (17).
The goal of the function is an arbitrary entity of GFO –- referred to
also as a chunk of the reality –- that is intended to be achieved by
each realization of the function. In the case of transporting goods,
the location of the goods at is the goal. The goal specifies
only the part of the world directly affected (or intended to be
affected) by the function realization. In our case, it is the relator of
goods being located at . Often a goal is embedded in a wider context,
being a complex whole, e.g. a fact, configuration, or situation, called
final state. A final state of a function includes the goal plus an
environment of the goal, therefore making the goal more comprehensible.
Here, it is the relator together with its relata, i.e., goods located in
- denotes a goal of ;
- denotes a functional item of .
Functions are dependent entities, in the sense that a function is
always the function of some other entity, executing it. The functional
item of the function indicates the role of entities executing a
realization of , such that all restrictions on realizations imposed by
the functional item are also stipulated by some goal of . In the
case of ``to transport goods'', the functional item would be the role
universal ``goods transporter''.
Entities are often evaluated against functions. This is reflected in
GFO by the relations of realization and realizer. Intuitively, an
individual realization of a function is an individual entity, in
which (and by means of which) the goal of is achieved in
circumstances satisfying the requirements of . Take the example of
function ``to transport goods from Leipzig to Berlin'', and the
individual process of transportation of goods by plane from Leipzig
to Berlin. In brief, we can say that the process starts when the
requirements of are satisfied, and ends by achieving the goal of ,
which, therefore, is the realization of function .
It is important to understand the difference between a function and a
realization, in particular with regard to their specification. To
specify a function and its structure one must state what will be
achieved; representing a realization usually means specifying how
something is achieved. Note that not all functions must be realized by
a process, as in the above example. In fact, in GFO we do not interpret
functions in terms of processes or behaviors as described in (50).
Apart from functions that are typically realized by processes or
behaviors, we also consider functions realized by presentials.
Consider, for instance, a pepper moth with
a dark covering sitting on a dark bark. This situation is the
realization of the function of camouflaging a moth.
In every realization we find entities that execute this realization.
They may be identified by references to functional items. For
example, for the function ``to transport oxygen'', the role ``oxygen
transporter'' is the functional item. Now consider an individual
transport process, i.e., a realization, involving a single red blood
cell. That cell has the role ``oxygen transporter'' within this
realization. This fact gives rise to a new entity that mediates between
the realization and the cell itself, namely the cell as an ``oxygen
transporter'' (cell-qua-oxygen transporter). Such an entity is called
the realizer of the function and is considered to be a qua-individual,
i.e., an instance of a role universal.
Functions are often ascribed to entities, e.g. the function of oxygen
transport is assigned to a process of blood circulation. We assign
functions to entities by the has-function relation, whose second
argument is a function, and the first is one of the following:
- an entity that is a realization of the function, e.g., for the
function of transporting oxygen, the process of blood circulation;
- an entity that plays the role of the realizer in a realization
of a function, e.g. the red blood cell in the process of blood
- an entity intended to be a realization or a realizer of a function.
The third case especially refers to artifacts that often inherit their
functions from the designer, who intends for them to realize particular
functions. The function ascription of that kind is called
intended-has-functions. Note that artifacts are not only understood to
be entities playing the role of realizers, as, e.g., a hammer that
plays a realizer of the function ``to hammer nails''. Additionally,
artifacts may play the role of realizations, e.g. the process of
transporting goods, which is a realization of the transport function, may
be an artifact as well. This holds true especially with regard to
The intended-has-functions have a normative character, which allows for
assigning such functions to entities that possess them as malfunctions.
In short, the entity that has an intended function , but is neither a
realization nor a realizer of , is said to be malfunctioning. The
flavors and more detailed specification of malfunctions and of other
notions outlined above can be found in (13).