Chapter 5: Including the Parts with the Whole

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Overview

In This Chapter

• Modeling the whole and its parts

• Differentiating between aggregation and composition

• Programming considerations for aggregates

• Showing parts within class boxes

When you model associations between classes, you find that UML treats one kind of association with special reverence. This particular association embodies the “whole-or-part-of” relationship that UML modelers call aggregation. Aggregation is just a fancy way of talking about a group of distinct objects (parts) gathered together to form some whole. In this chapter we define aggregation and its stronger form—composition. We demonstrate the UML notation for aggregation and explain why it holds a special place among associations in the world of object-oriented modeling and programming.

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