Composition

As in the natural world, the metaphor of objects implies a constructed environment. Objects are compositions of other objects. You can define most tasks supported by applications as a specialized combination or set of relationships between objects. A text document is a composition of text, paragraphs, footnotes, or other items. A table is a combination of cells; a chart is a particular organization of graphics. When you define user interaction with objects to be as consistent as possible at any level, you can produce complex constructions while maintaining a small, basic set of conventions. These conventions can apply throughout the interface, increasing ease of use. In addition, using composition to model tasks encourages modular, component-oriented design. This allows objects to be adapted or recombined for other uses.