Compositionhas

Compositionhas is a term used in software design and ontology modeling to denote a strong containment relationship between two entities, where one object or concept (the container) owns and manages another (the component) through composition.

Under compositionhas, the component does not exist independently outside the container's lifecycle; the container is responsible for creating, configuring, and destroying the component. This contrasts with looser forms of 'has' relations, such as aggregation or plain association, where the component may outlive the container or be shared.

In UML and many programming patterns, the composition relationship is represented by a filled diamond or by explicit ownership semantics. In code, it is typically enforced by means of exclusive ownership pointers or by embedding objects within the container's state.

Use cases include representing hierarchical data structures, complex objects that are composed of tightly coupled parts, and domain models where component lifecycles are bound to the parent. The term aligns with the design principle of composition over inheritance, emphasizing collaboration and encapsulation through contained components.

Criticism notes that excessive composition can increase coupling and complexity, making testing and reuse harder. Proponents argue that when lifecycles are tightly bound, composition provides clear ownership and fewer surprises.