Two entity types have an aggregating relationship when:
The existence of the target entity type depends on the source entity
type, i.e. the lifespan of an instance of the target entity type is
less than or equal to the lifespan of the instance of the source entity type.
The target entity type is created by the source entity type, i.e. the source entity type can directly influence the attributes.
At least one other different source entity type is involved in the creation of the target entity type.