Other association characteristics
Aggregation
Aggregation is a special form of association, indicating that one of the entities contains the other.
Example of aggregation:
A car includes a chassis, an engine, and wheels.
To define the aggregation between the "Car" and "Motor" entities:
1. Right-click the role played by the "Car" entity in its association with the "Motor" entity and select Properties.
Role properties appear.
2. Click Characteristics.
3. In the Whole/Part field, select "Aggregate".
A diamond now appears on the role, representing the aggregation.
In HOPEX Windows Front-End you can specify aggregation directly from role's pop-up menu.Composition
A composition is a strong aggregation where the lifetime of the components coincides with that of the composite. A composition is a fixed aggregation with a multiplicity of 1.
Example of composition:
An order consists of several order lines that will no longer exist if the order is deleted.
Composition is indicated by a black diamond.
To specify composition of a role:
1. Right-click the role and select Properties.
Role properties appear.
2. Click the drop-down list then Characteristics.
3. In the Whole/Part field, select "Composite".
In HOPEX Windows Front-End you can specify composition directly from role's pop-up menu.