a detailed comparison of corba, dcom and java/rmi
(with specific code examples)
introduction
distributed object computing extends an object-oriented programming system by allowing objects to be distributed across a heterogeneous network, so that each of these distributed object components interoperate as a unified whole. these objects may be distributed on different computers throughout a network, living within their own address space outside of an application, and yet appear as though they were local to an application.
three of the most popular distributed object paradigms are microsoft's distributed component object model (dcom), omg's common object request broker architecture (corba) and javasoft's java/remote method invocation (java/rmi). in this article, let us examine the differences between these three models from a programmer's standpoint and an architectural standpoint. at the end of this article, you will be able to better appreciate the merits and innards of each of the distributed object paradigms.
corba relies on a protocol called the internet inter-orb protocol (iiop) for remoting objects. everything in the corba architecture depends on an object request broker (orb). the orb acts as a central object bus over which each corba object interacts transparently with other corba objects located either locally or remotely. each corba server object has an interface and exposes a set of methods. to request a service, a corba client acquires an object reference to a corba server object. the client can now make method calls on the object reference as if the corba server object resided in the client's address space. the orb is responsible for finding a corba object's implementation, preparing it to receive requests, communicate requests to it and carry the reply back to the client. a corba object interacts with the orb either through the orb interface or through an object adapter - either a basic object adapter (boa) or a portable object adapter (poa). since corba is just a specification, it can be used on diverse operating system platforms from mainframes to unix boxes to windows machines to handheld devices as long as there is an orb implementation for that platform. major orb vendors like inprise have corba orb implementations through their visibroker product for windows, unix and mainframe platforms and iona through their orbix product.
