The role is a function fulfilled by an existing entity during a particular situation. This function ceases to exist at the same time as the entity. A role is optional and does not allow the entity to be uniquely defined. The same entity can change roles during its life cycle, or have several distinct roles in the same situation.

a realizable entity that exists because the bearer is in some special physical, social, or institutional set of circumstances in which the bearer does not have to be, and is not such that, if this realizable entity ceases to exist, then the physical make-up of the bearer is thereby changed. A role is thus laways optional. source Building Ontologies with Basic Formal Ontology.

The role is a function fulfilled by an existing entity during a particular situation. This function ceases to exist at the same time as the entity. A role is optional and does not allow the entity to be uniquely defined. The same entity can change roles during its life cycle, or have several distinct roles in the same situation.