Composition

Composition is a strong whole-part Relationship in which the Whole has Structural Ownership of the Part. A Part belongs to at most one composite Whole at a time, and its existence, Lifecycle, and Invariants are managed consistently with the boundary of the Whole.

In UML 2.5.1, Composition is a binary Association whose Association End has the Aggregation Kind composite . The composite Object is responsible for the existence and storage of its Parts, and the upper Multiplicity at the composite end is one. SimpleModeling adopts this meaning and uses it to determine domain Lifecycle and Invariant boundaries.

Ordinary composition, function composition, and visual or audio compositing are not the whole-part Relationship defined by this term. Composition is also distinct from Aggregation, which may represent a shared Part.

Composition establishes a Lifecycle and Invariant boundary on the Object side. It is distinct from function composition on the Functional side, and the shared short label does not make the concepts identical.

CML (Cozy Modeling Language) can explicitly describe an Association as Composition. Composition is not inferred merely from shared persistence, field containment, or parent-child presentation.

Scala has no language construct that maps one-to-one to Composition. Fields, case classes, collections, and nested Types may help realize it, but do not by themselves express Structural Ownership.

Collections, Groups, Schemas, and related simplemodeling-lib constructs may realize a composite structure, but using those Types alone does not establish domain Composition.

Japanese articles and videos use 合成関係（Composition） at first occurrence and shorten it to 合成 only while the same whole-part context remains established. Ordinary Japanese usage and functional-programming uses of 合成 are not automatically linked to this term.