ispartof

isPartOf is a binary relation used in knowledge representation to express that one entity is a constituent of another. When A isPartOf B, A is a component or portion that belongs to B. The relation is commonly used to describe structural, functional, or compositional relationships across domains such as biology, engineering, documents, and geography.

Semantics and properties of isPartOf vary by domain, but several common characteristics appear in many ontologies. isPartOf is typically transitive: if A isPartOf B and B isPartOf C, then A isPartOf C. It is usually irreflexive (an object is not considered a part of itself) and often treated as asymmetric or antisymmetric to discourage cycles. The inverse relation is hasPart, meaning that if A isPartOf B, then B hasPart A. Some frameworks distinguish between proper parts and parts in general, with isPartOf commonly referring to proper parts.

In ontology design, isPartOf is often modeled as an object property with characteristics such as transitivity and an inverse hasPart. It is used to encode hierarchical or compositional structures without equating an entire entity with its parts. It frequently appears alongside other relations such as partOf, hasPart, and contiguous or functional relations depending on the domain.

Examples of isPartOf use include a wheel isPartOf car, a chapter isPartOf book, a leaf isPartOf a tree, and a component isPartOf a system. In biological contexts, organs arePartOf an organism, and cells arePartOf tissues, depending on the level of granularity.

See also: hasPart, partOf, mereology.