in the relationship that involves the entities PURCHASE_ORDER and SALES_CENTER, a purchase order must come from one, and only one, of the sales centers. thus, the minimum-maximum cardinality is (1, 1) for the entity SALES_CENTER. on the other hand, a sales center must have at least one purchase order and there is an unspecified upper bound. therefore, the minimum-maximum cardinality is (1, N) for PURCHASE_ORDER