Sometimes the primary UML diagrams, such as class and sequence diagrams, are not a perfect match for capturing certain details about your system. Composite structures help fill some of those gaps. Composite structures show how objects create a big picture. They model how objects work together inside a class, or how objects achieve a goal. Composite structures are fairly advanced, but they're good to have in your bag of tricks because they are perfectly suited for specific modeling situations, such as showing:

Show design patterns in your software and, more generally, objects cooperating to achieve a goal Composite structures provide a view of your system's parts and form part of the logical view of your system's model,