Final answer:
The statement asserting that an entity identifier can be either unique or nonunique is true. Entity identifiers are vital in database design, with primary keys being unique and secondary keys potentially being nonunique.
Step-by-step explanation:
The statement that an entity identifier can be either unique or nonunique is true. In database design and data modeling, an entity identifier is a way to uniquely identify each instance of an entity. Being unique is a critical feature of a primary key, which serves as the main entity identifier for a table within a database. However, there are also nonunique identifiers, known as secondary keys or alternate keys, which may identify more than one instance of an entity. These keys are used for purposes other than the primary identification, such as sorting or searching based on nonunique attributes.
For example, a Social Security Number (SSN) is unique to every individual and can serve as a primary key in a database holding personal records. On the other hand, a person's surname might be used as a secondary key; it helps to organize or find records but is not unique, as multiple individuals can share the same surname.