Which of the following characteristics pertaining to databases is not true?

A. A data model should exist and all entities should have a significant name.

B. Justifications must exist for normalized data.

C. No NULLs should be allowed for primary keys.

D. All relations must have a specific cardinality.

Justifications should be provided when data is renormalized, not when it is normalized, because it introduces risk of data inconsistency. Renormalization is usually introduced for performance purposes.

Source: Information Systems Audit and Control Association, Certified Information Systems Auditor 2002 review manual, Chapter 3: Technical Infrastructure and Operational Practices (page 108).