The object paradigm is to be reconsidered for distributed systems

The information hiding property states a clean distinction between external visibility and internal perspective of an object. The external world has reduced visibility of the inside of an object: normally only an interface constitued by operation names is visible. Within any object, instead, there is the full visibility, in particular of the object state. This makes possible thateach object decides its internal policies independently of any environment decision. Object communications produce the global computation in object-based systems. An object can communicate with another if and only if knows it via a reference [Lis79]. In object systems, a communication implies that client objects request operations defined in the interface of server objects. These requests are exchanged by using message-passing mechanisms. Dynamicity of communications means that an object can change its visibility, i.e. the objects it can refer. Classification and factorization by inheritance gives object environments the possibility of applying reusability and extensibility. On the one hand, object applications can be designed and programmed by reusing already developed software. On the other hand, applications based on objectscan evolve to follow changes of specification. In the case of dynamic changes, the possibility of updating classes at run-time constitutes an useful tool.