A definitional business rule prescribes how information may be derived, inferred, or calculated based on existing business data. These rules establish precise meaning and categorization of data, ensuring that terms and concepts are consistently understood and used within the organization.

Examples include:

Calculation rules (e.g., interest = principal × rate × time)

Classification rules (e.g., customers with purchases over $10,000/year are premium)

In contrast, behavioral business rules govern constraints or conditions on how actions must be performed.

BABOK® Reference:

Discussed under the Strategy Analysis and Requirements Analysis and Design Definition knowledge areas, definitional business rules are explained as fundamental to maintaining business consistency and logical integrity.