The UML Composite Structure diagram enables you to model the internal structure of a class and the collaborations that the class structure makes possible.
This diagram can include internal parts, ports through which the parts interact with each other or through which instances of the class interact with the parts and with the outside world, and connectors between parts or ports.
According to the UML spec, a composite structure is a set of interconnected elements that collaborate at runtime to achieve some purpose.
The Composite Structure diagram enables you to model:
•Part: represents a role played at runtime by one instance of a classifier or by a collection of instances. The part can only name the role, it can name an abstract superclass, or it can name a specific concrete class.
•Ports: interaction points that can be used to connect structured classifiers with their parts and with the environment. Ports can optionally specify the services they provide and the services they require from other parts of the system.
•Connector: a relationship that binds two or more artifacts together, allowing them to interact at runtime. The connector is shown as a line between some combination of parts, ports, and structured classifiers.
•Collaboration: generally more abstract than a structured classifier, it contains roles that instances can play in the collaboration.
•Structured Classifiers: Model artifacts whose behavior can be completely or partially described through interactions between parts.
•Encapsulated classifier: An EncapsulatedClassifier is a type of structured classifier that contains ports.