What principle does entity integrity enforce in a database?

Entity integrity is a fundamental principle in relational database management that guarantees that each row, or tuple, in a table is uniquely identifiable. This is accomplished by ensuring that every table has a primary key which must be unique and cannot contain null values. A primary key serves as a unique identifier for a record, allowing for distinct identification of each entry in the table.

By enforcing that each tuple possesses a unique primary key that is not null, entity integrity helps prevent duplicate entries and enables proper referencing among tables. This is crucial for maintaining the accuracy and consistency of the data housed within the database, allowing relationships to be established correctly through foreign keys linked back to unique primary keys.

In contrast, the other options do not accurately represent the concept of entity integrity. Foreign keys, attributes needing to be unique, or the requirement of multiple primary keys do not align with what entity integrity mandates. The focus is solely on the uniqueness and non-null nature of primary keys for each tuple, solidifying the integrity of the data structure.