threeplace

Threeplace is a term used across several disciplines to denote a relation or predicate involving three components, but it lacks a single, universally adopted definition. In mathematics and logic, a three-place (or ternary) relation is a relation among three elements, written R(x, y, z). It is true when the triple satisfies a specified condition, such as R(x, y, z) holding if x + y = z. Ternary relations generalize binary relations and can model coordinates, betweenness, or functional constraints.

In linguistics, three-place predicates (also called ditransitives) encode three semantic participants: agent, patient, and recipient or goal. Examples include verbs like give, send, or tell. Syntactic realizations vary: double-object constructions or prepositional indirect objects, with subject–verb–indirect object–direct object sequences in languages that permit them.

In computing and information science, three-place relations appear in knowledge representation as higher-arity relations or as triples in RDF-like structures, where three elements form a basic unit such as subject–predicate–object. Extended systems store higher-arity relations using reified nodes or explicit tuples.

There is also occasional use of "threeplace" as a brand name or project title. In the absence of a canonical entity, the term is primarily encountered as a descriptive shorthand for arity-three relations.

See also: arity, ternary relation, three-place predicate, ditransitive, triple store, RDF triple.