A component can be decomposed into a group of components. A grouping of components is called a system. A component that is decomposed into a system has no own behaviour definition, the behaviour of the system is defined by the components into which it is decomposed.
The components within a system can also be composite components, so it is possible to define systems of systems.
Composite components can also expose ports of contained components by binding their own provided or required ports or ports of contained components. In that case the binding looks like
port <=> component1_instance_name.port