Each link may be realized by something as simple as a pointer or by something as complex as a network connection, and may represent the possibility of instances being able to communicate because their identities are known by virtue of being passed in ...

Each link may be realized by something as simple as a pointer or by something as complex as a network connection, and may represent the possibility of instances being able to communicate because their identities are known by virtue of being passed in as parameters, held in variables or slots, or even because the communicating instances are the same instance.