We look at formal approaches in Chaoter Five. This in turn aids clear design and implementation of a system. The implementation of the object is accessed by a collection of methods only, and there are several mechanisms used to implement invokation of a method. Typically message passing is used in centralized Object Oriented Systems. This is also the case in distributed systems.
Message Passing One process sends a message to another.
Once the primitive send operation has completed, the sender is unaware of the fate of the message. At some later stage, the receiver may issue a receive operation, or not. It may fail. In practice, the level of granularity of Objects in a Distributed System will be larger than that of centralized object oriented systems. Remote Procedure Call A process in one address space executes a procedure in another address space.