In the context of domain constraints, which element is used to define allowed values?

• A. Primary keys
• B. External indexes
• C. Allowed value lists
• D. Anonymous data

Answer: (C)

Domain constraints control what values an attribute can legally hold by listing the allowed options. The element used to define those allowed values is the allowed value list, an enumerated set that specifies each permissible value. This is how you ensure data like a status field remains within a defined set such as Active, Inactive, or Pending.

Other options don’t perform this constraint role: a primary key enforces unique row identification, not allowable values for a domain; external indexes help with lookup speed but don’t restrict data content; anonymous data isn’t a mechanism for enforcing value constraints.