Answer: Distributed Object Models — Comparison of CORBA, DCOM, and EJB

1. What is a Distributed Object Model?

A Distributed Object Model (DOM) is an architectural paradigm in distributed computing where software objects located on different physical machines across a network can communicate and invoke methods on one another as if they were residing in the same local memory space.

+-----------------------+                            +-----------------------+
|     Client System     |                            |     Server System     |
|                       |                            |                       |
|   [Client Program]    |                            |   [Remote Object]     |
|          |            |                            |          ^            |
|          v            |                            |          |            |
|     [Stub/Proxy]      |                            |   [Skeleton/Adapter]  |
|          |            |                            |          ^            |
|          v            |                            |          |            |
|    [ORB / Runtime]    | === Network Communication => |    [ORB / Runtime]    |
+-----------------------+       (IIOP / RPC / RMI)   +-----------------------+

Core Mechanisms:

• Stub (Client Proxy): Marshals method parameters and serializes calls across the network.
• Skeleton / Dispatcher: Unmarshals parameters on the remote server, invokes the actual method, and serializes the return value back.

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2. Overview of CORBA, DCOM, and EJB

A. CORBA (Common Object Request Broker Architecture)

• Specification: Defined by the Object Management Group (OMG) as an open vendor-neutral standard.
• Key Feature: Truly platform-independent and language-independent. Interfaces are defined using OMG IDL (Interface Definition Language).
• Communication: Uses an ORB (Object Request Broker) and communication protocol IIOP (Internet Inter-ORB Protocol).

B. DCOM (Distributed Component Object Model)

• Specification: Developed by Microsoft as a network extension of COM (Component Object Model).
• Key Feature: Deeply integrated into Windows OS; uses Microsoft RPC (Object RPC).
• Limitation: Windows-centric and proprietary, with limited cross-platform interoperability.

C. EJB (Enterprise JavaBeans)

• Specification: Developed by Sun Microsystems / Oracle (now part of Jakarta EE).
• Key Feature: Pure Java-centric server-side component architecture for building transactional, secure, scalable enterprise business logic.
• Container Architecture: Runs inside an EJB Container that automatically handles transactions, security, concurrency, connection pooling, and lifecycle.

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3. Detailed Comparison Matrix

Parameter	CORBA	DCOM	EJB
Governing Body	Object Management Group (OMG)	Microsoft	Sun / Oracle / Jakarta EE
Platform Support	Platform Independent (Unix, Linux, Windows)	Windows Centric (Limited Unix support)	Cross-Platform (Any Java-supported OS)
Language Support	Multi-language (C++, Java, Python, Ada, COBOL)	Multi-language on Windows (C++, VB, C#)	Java Only
Interface Definition	OMG IDL (Interface Definition Language)	Microsoft IDL (MIDL)	Java Interfaces (Local / Remote)
Underlying Protocol	IIOP (Internet Inter-ORB Protocol)	ORPC (Object Remote Procedure Call)	RMI / IIOP
Enterprise Services	Basic CORBA services (Naming, Event, Security)	Microsoft MTS / COM+	Full Container Services (JTA, JPA, Security, Pooling)
Architecture Model	Client-Server with ORB middleware	Binary COM components over network	Component-Container model
Primary Strength	Universal vendor & language interoperability	High performance on Windows enterprise environments	Rapid enterprise development with built-in declarative services
Weakness	Steep learning curve, complex configuration	Windows lock-in, poor firewall traversal	Restricted to Java ecosystem

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Conclusion

• CORBA is ideal for heterogeneous legacy integration across multiple programming languages and OS platforms.
• DCOM provided high performance in pure Microsoft Windows environments before modern Web APIs.
• EJB remains the enterprise standard for pure Java distributed systems, offering automated transactional and container-managed persistence capabilities.