In UML modeling, you can specify the services that a
component needs to perform its functions and to fulfill its own obligations
to its clients.
A diagram must be open in the diagram editor and
it must contain at least one component and one interface.
To specify a required interface, in the diagram editor,
click an interface and drag it over the Required Interfaces compartment
of the component.
If the component is showing the external view, the required
interface is displayed as a socket attached to the component shape.
If the component is showing the internal or class view, the interface
is displayed in the Required Interfaces compartment.