Subrules

Subrules are subordinate rules within a rule-based system, designed to specify exceptions, refinements, or context-specific applications of a primary rule. They help manage complexity by dividing a general directive into more precise components.

In many systems, subrules form a hierarchy where each subrule is linked to a parent rule. Subrules may refine the conditions under which the parent applies, impose additional requirements, or override the parent under certain circumstances. The activation of subrules depends on the system’s evaluation strategy, which may favor the most specific rule, apply rules in a stated order, or evaluate all applicable rules and combine their effects.

Examples of subrules appear across domains. In legal codes, a general prohibitive rule like “no vehicles in the park” may have subrules that permit certain categories of vehicles or specify time-based exceptions. In grammar, a main production rule such as a sentence structure can have subrules governing agreement, punctuation, or tense. In software, a policy engine or business rule system uses subrules to handle context-specific decisions, such as “if user is admin and action is delete, require two-factor authentication.” In games, subrules clarify edge cases (for example, how light weapons operate in fog).

Design considerations include ensuring non-contradiction among rules, clear scope and hierarchy, and documentation so users understand how subrules interact. Testing should cover typical and edge cases to avoid conflicts or unintended overrides.

See also: rules, rule-based systems, hierarchical organization, exception handling, policy engines.