General Formal Ontology (GFO)
Starting with a role , there are two directly related notions,
namely player and context.26 Each role
requires a player and a context . More precisely, is one-sidedly
existentially dependent on , and mutually existentially dependent
with . Two basic relations connect entities of these types:
plays, denoted as , connecting a player with a
role ,27 and role-of (),
which ties a role to its context . In terms of the ``standard''
role example of student, John
plays the role of the student in the context of his
relationship to his university. Other examples refer to John as an
employee in the context of some company, or as a mover of some
pen, in the context of that movement.
Moreover, apart from roles, players, and contexts, roles are often
contrasted with natural universals28, cf. (27). While ``student'' is a role, ``human'' is
not a role, but a natural universal that provides players for roles.
Intuitively, roles can be distinguished from natural universals by their
dependence on a context, whereas for natural universals, the context of
the considered role is irrelevant.
Each of these categories discussed thus far are self-contained, in the sense
that they do not provide insights on how they are related to other GFO
categories in this work. To establish these links, we first note that
there are individuals as well as categories of roles (and all other
notions). For more specific relations, different types of roles need to
be distinguished. This classification is based on the contexts of roles,
because the coupling of roles and contexts is more tight than between
players and roles, cf. (37).