What is a participation role?

Participation role signifies role that a participating entity from the entity type plays in each relationship instance, and helps to explain that relationship means. Using Role name is not necessary in the description of relationship types where all participating entities are distinct because in such case name of entity types generally specify the role played by each entity type. But when one entity type participate in a relation in more than one role; recursive relationship; it becomes necessary to use role names in the description of relationship type.