Which of the following best describes the role of a check constraint in database design?

The role of a check constraint in database design is fundamentally to enforce business rules regarding data validity. When a check constraint is applied to a database column, it defines conditions that the data must meet for it to be considered valid. For instance, if a column is designated to hold age values, a check constraint could ensure that the entries are non-negative integers. This capability means that the constraint prevents invalid data from being inserted into the database, thereby helping maintain data integrity and ensuring that the business rules that govern the data's appropriateness are adhered to.

While other options touch on relevant aspects of data management, they do not accurately capture the primary function of check constraints. Ensuring data entry matches a specific format is typically handled by other types of constraints, such as format or validation constraints. Improving query performance relates more to indexing or optimization techniques rather than data integrity rules enforced by constraints. Elimination of duplicate entries is managed through unique constraints, which serve a different purpose than check constraints. Thus, option B best encapsulates the intended function of a check constraint in ensuring that only valid data enters the database according to established business rules.