gather

gather

ju ji

Aggregation is a special form of association. Aggregation represents the relationship between classes as a whole and a part. A car with four wheels, a steering wheel, an engine and a chassis is an example of clustering. In the requirement analysis, it includes, constitutes and divides into Parts are often designed as aggregation relationships. Aggregation can be further divided into shared aggregation and composition. For example, a research group contains many members, but each member can be a member of another research group, that is, a part can participate in multiple entirety, which is called shared aggregation. The other is that the whole has its parts, and the parts coexist with the whole. If the whole does not exist, the parts will disappear, which is called composition. For example, we open a view window, which is composed of title, frame and display area. Once it disappears, all parts disappear at the same time. In UML, aggregation is represented as a hollow diamond and composition as a solid diamond.

Aggregation is an optimization measure.



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