Which statement describes the semantics of a Property that has the aggregation kind composite?

Which statement describes the semantics of a Property that has the aggregation kind composite?

A. The aggregation kind composite is semantically equivalent to namespace containment

B. Instances of the composed object’s type can exist only in the context of the composite object.

C. When the Property’s composite object ceases to exist, all of its composed objects also cease to exist.

D. The Property’s composed objects are part of a subset and the composite object is a union of the defined subsets.

View Answer

Answer: C

Explanation:

In UML, the aggregation kind ‘composite’ is one of the two types of aggregation, shared and composite. Composite aggregation, also known as composition, implies that the composed objects do not have a separate lifecycle from the owner object and are parts of the whole. This is in contrast to shared aggregation (aggregation), where the parts can be shared with different owners and have their own lifecycle.

Let’s look at the options:

A. Composite aggregation implies ownership and is related to, but not equivalent to namespace containment. Namespace containment is more about the scope for named elements rather than lifecycle management.

B. While it’s true that instances of the composed object’s type are often associated only with the composite object, the key aspect of composite aggregation is not just the exclusive context but the lifecycle dependency, which is not captured in this option.

C. This option is correct because, in UML, composite aggregation (composition) implies that the parts are existentially dependent on the whole. When the composite (whole) object is destroyed, so are all of its parts, indicating a strong lifecycle dependency between the composite object and its composed parts.

D. This option describes a relationship more akin to set theory than UML composition. In UML, composite aggregation doesn’t deal with subsets and unions in the context of set theory.

Thus, the most accurate answer, according to the UML specification regarding composite aggregation, is C: When the Property’s composite object ceases to exist, all of its composed objects also cease to exist.