Types are concerned with the specification of uniform structural characteristics and behavioral characteristics. Types may be explicitly related to classes, where a class receives an interface from a type and provides an implementation for the interface, or types may be implicitly related to classes, where a class defines an interface and provides an implementation. Fundamentally, types are descriptions of objects with common attributes, operation interfaces, semantics, associations, and interactions. There are various other concepts regarding objects and classes that are not discussed above. Return to Contents Links and Associations Links and associations abstract relationships among entities.
Links are representational constructs of entities that relate other entities.
Links are instances of associations. Fundamentally, links are abstracted relationships among objects. Associations are descriptions of links with a common implementation. Aggregations are associations that specify a whole-part relationship among an aggregate and component parts. Compositions are aggregations with strong ownership and coincident lifetime constraints among a composite and component parts.