GFO Part I Basic Principles
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12.2 Classification of Roles

Based on the literature, the following categories serve as contexts in various role approaches: relations, processes, and (social) objects. Accordingly, we distinguish three role types with the following informal definitions:

  • A relational role corresponds to the way in which an argument participates in some relation;
  • A processual role corresponds to the manner in which a single participant behaves in some process;
  • A social role corresponds to the involvement of a social object within some society.

Note that relational and processual roles have been discussed earlier, in the sections on their corresponding context categories (see sect. 8 and 10, respectively). Here, we focus on the relationships to the general role notions identified above. Moreover, the given classification is not meant to be complete, i.e., other categories may be contexts, thus yielding further role types.

12.2.1 Relational Roles

Relators are the contexts of relational roles, i.e., a relator can be decomposed into at least two relational roles which complement each other. Intuitively, the role-of relation seems like a part-of relation in this case. Because relational roles refer to exactly one player, the plays relation corresponds to has-property. Accordingly, relational roles are subsumed by the category of properties.

Consider that the number two is a factor of four. This refers to a relator with two role individuals, one instantiating the role universal ``factor'', the other instantiating ``multiple''. The first of these role individuals is played by two, while four plays the second role individual.

The generality of relations regarding the entities they connect is reflected in the fact that players of relational roles cannot be restricted by any specific category; hence, the natural universal for relational roles in general is the category ``entity''.

12.2.2 Processual Roles

Processual roles have processes as their contexts. As such they are processes themselves, and sect. 8.1 identifies them as special layers of a process, because role-of is understood as a part-of relationship (as in the case of relational roles). The plays relation is different from plays for relational roles, because here plays corresponds to participation in a process.

When John moves a pen, for example, the movement is a process in which John and the pen are involved, in different ways. Accordingly, the process can be broken into two roles, ``the mover'' and ``the moved''. John plays the first role, the pen the second. Imagining John as a mime who pretends to move a pen should provide a natural illustration of the notion of processual roles.

The case of the mime further exemplifies an uncommon case of roles: a single processual role may itself form a context. Almost all role notions are relational in nature, in the sense that their contexts are composed of several roles. In contrast, processes that comprise only a single participant are understood as a processual role, and likewise, as a context. Considering the plays relation, the potential players of processual roles are restricted to persistants, because a persisting entity is required to carve out roles from processes.

Note that the similarities of relational and processual roles leads to a category of abstract roles. The latter is functionally defined as providing ``a mechanism of viewing some entity –- namely the player -– in a defined context'' (37). Given this abstraction, we can now introduce a final type.

12.2.3 Social Roles

Social roles differ from abstract roles in that their understanding depends much less on their context. Instead, social roles come with their own properties and behavior, which is a common requirement in many role approaches in computer science, cf. (55). For example, if John is a student, he is issued a registration number and gains new rights and responsibilities. From a philosophical perspective, this view is further inspired by Searle (51) and the ontological levels of Poli (45), see sect. 4.

Social roles are considered to be social structures in GFO, which is an analogous category to material structures, but in the social stratum. However, social roles also need a foundation on the material level, which in general role terms corresponds to the plays relation. For instance, the human John plays a social role that is characterized by specific rights and responsibilites. Note that so far we do not exclude that social roles themselves may play other social roles; hence, there may be chains of the plays relationship that must ultimately terminate by a role played by a material structure.

The contexts of social roles are also social structures, which may be called societies or institutions, cf. (51). Accordingly, a rough similarity between role-of and part-of is present for social roles as well. However, there are complex interrelations among entities of the social stratum, and the ontology of this stratum requires much more work.

Robert Hoehndorf 2006-10-18


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