4.1 Composition viewpoint for library management system

The Composition viewpoint describes the way the design subject is (recursively) structured into constituent parts and establishes the roles of those parts. Software developers and maintainers use this viewpoint to identify the major design constituents of the design subject, to localize and allocate functionality, responsibilities, or other design roles to these constituents.

UML component diagrams can show composition and modular assembly of systems in terms of subsystems. Alternatively, a hierarchical decomposition diagram with natural language descriptions of purpose and function for each entity can be used.