Subsumes

Subsumes is a relational verb used primarily in logic, mathematics, and knowledge representation to denote that one concept, class, or type is more general than another. When A subsumes B, every instance of B is also an instance of A; equivalently, B is contained within A. In set theory this is expressed as B is a subset of A (B ⊆ A). The relation is reflexive (A subsumes A) and transitive (if A subsumes B and B subsumes C, then A subsumes C), forming a partial order on the domain of concepts or sets. In taxonomy and ontology, subsumption corresponds to the hypernym–hyponym relation: a general class (the hypernym) subsumes specific classes (hyponyms). For example, Mammal subsumes Dog, since every dog is a mammal.

In logic and description logics, subsumption is used to relate concepts and to structure reasoning about class hierarchies. In databases and knowledge graphs, subsumption underpins class hierarchies and inference rules. In programming language theory, subsumption relates to subtyping: if B is a subtype of A, values of B can be used wherever a value of A is expected, which can be phrased as A subsumes B in the type system.

The term derives from Latin sub- 'under' and sumere 'to take up'. Usage is generally formal and domain-dependent, with subtle differences across disciplines but a common core: inclusion of the more specific within the more general.