What aspect would be most important for the IS auditor to focus on when reviewing the integrity of a database?

Focusing on foreign key relationships is crucial when reviewing the integrity of a database because these relationships establish the connections between tables that ensure data consistency and accuracy. Foreign keys act as a constraint that enforces referential integrity in relational databases; they ensure that a value in one table corresponds to a value in another, preventing orphaned records or data anomalies.

When foreign key relationships are correctly defined and maintained, they help to enforce the logic and structure of the data model, ensuring that the data across related tables remains consistent. This is essential for maintaining the integrity of data, as it prevents unauthorized or erroneous data entries that could lead to flawed reporting or analysis.

While other aspects, like field definitions, master table structures, and denormalization, are important in their own right, they do not directly relate to the immediate enforcement of data integrity across the database. Field definitions focus on the format and constraints of individual columns, the master table structure relates to the overall design, and denormalization generally involves altering the database structure for performance efficiency, which may compromise integrity if not managed properly. Thus, the examination of foreign key relationships provides a more direct measure of how well the database maintains its integrity.