(1) Re-examine one-to-one (1:1) relationships In the identification of entities, we may have identified two entities that represent the same object in the enterprise. For example, we may have identified the two entities Client and Renter that are actually the same; in other words, Client is a synonym for Renter. In this case, the two entities should be merged together. If the primary keys are different, choose one of them to be the primary key and leave the other as an alternate key.