Messages sent to an object are forwaded to the space in which the object really exists, before being executed. Access to an object almost always must be made in a message-passing style. In contrast to shared memory systems, only one copy of a shared object ever exists. A remote reference can take several forms. The SSP Chains mechanism Two key components in the SSP Chains system are stubs and scions.
Stubs represent remote references.
They implement the same interface as the referenced object, which means the application program can invoke methods in the stubs as if they were the object that they represent. The scion is connected to the target object. It receives incoming messages and converts them back into method invocations, then invokes the method in the target object. Scions are treated as roots for any local garbage collector which might be present. They protect the object to which they point from being deleted.