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A one-to-many unary relationship allows an occurrence of the entity type on the "one side" of the relationship to be associated with 1) a single occurrence of the same entity type 2) multiple occurrences of the same entity type 3) a single occurrence of the different entity type on the "many side" of the relationship 4) multiple occurrences of the different entity type on the "many side" of the relationship 5) multiple occurrences of the different entity type on the "one side" of the relationship