Underbroadness

Underbroadness is a term used in formal methods and verification to describe a situation where a specification is too weak to adequately capture the intended behavior of a system. It is the opposite of overbroadness, where a specification is too restrictive. A specification suffers from underbroadness if it allows for valid system behaviors that are actually undesirable or incorrect according to the system's true requirements.

This issue arises when the formal model or specification omits certain constraints or properties that are implicitly understood or crucial for the system's correct functioning. For instance, a system might be specified to always produce an output, but an underbroad specification might not explicitly state that the output must be positive, even if that is a fundamental requirement. Consequently, a system that produces a negative output might still be considered compliant with the underbroad specification.

Detecting underbroadness often requires a deep understanding of the system's domain and intended use. It is typically uncovered through testing or through reviewing the specification against known or anticipated failure modes. Fixing underbroadness involves refining the specification to include the missing constraints or properties, thereby making it a more accurate and complete representation of the desired system behavior. This process is essential for ensuring that the verified system truly meets its design goals.