Defining a reference for any service component in an application makes that reference available to every service component in the application. For example:

switchyard add-reference --referenceName Hello --interfaceType java --interface org.example.greeting.Hello --componentName Greeting

Will define a <reference> on the 'Greeting' component. This reference can be used by a 'Welcome' component in the same application without defining the <reference> to Hello in that component.