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The Distributed Object Approach

Object-oriented languages, such as C++ or JAVA, provide significant advances over standard procedural languages with respect to the reusability and modularity of code:

Whereas ``standard'' object-oriented programming (OOP) languages can be used to build monolithic programs out of many object building blocks, distributed object technologies (DOOP) such as OMG's CORBA [[(OMG)1997]] or Microsoft's DCOM [[Microsoft1996]] allow the creation of programs whose components may be spread across multiple machines. To implement a client-server relationship between objects, distributed object systems use a registry mechanism (CORBA's registry is called an Object Request Broker, or ORB) to store the interface descriptions of available objects. Through the ORB's services, a client can transparently invoke a method on a remote server object; the ORB is responsible for finding an object that can implement the request, passing it the parameters, invoking its method, and returning the results. The client does not have to be aware of where the object is located, its programming language, its operating system, or any other system aspects that are not part of an object's interface.

Although distributed objects offer a powerful paradigm for creating networked applications, certain aspects of the approach are not perfectly tailored to the constantly changing environment of the Internet. A major restriction of the DOOP approach is that the interactions among objects are fixed through explicitly coded instructions by the application developer. This implies that it is very difficult to reuse an object in a new application without bringing along all its inherent dependencies on other objects (embedded interface definitions and explicit method calls). Another restriction of the DOOP approach is the result of its reliance on a remote procedure call (RPC) style of communication. Although easy to debug, this single thread of execution model does not facilitate programming to exploit the potential for parallel computation that one would expect in a distributed environment. In addition, RPC uses a blocking (synchronous) scheme that does not scale well for high-volume transactions.


next up previous
Next: Mobile Objects Up: Technologies for Distributed Computing Previous: Technologies for Distributed Computing

Adam Cheyer
Mon Oct 19 17:14:26 PDT 1998