This example shows the importance of the existence unique object identifiers (OID's) in a object database. Unique tuple identifiers do not exist in a relational database. In the family tree below, all the relatives show were still alive after the end of World War II. Any relatives in this family tree deceased prior to the end of World War II and the introduction of National Insurance numbers in the United Kingdom would not be accessible directly in a relational database. In an object database these deceased persons would be directly accessible in an object database by using their respective OID's.