objectrequestbroker

An object request broker (ORB) is a middleware architecture that enables communication between clients and servers in distributed object systems. It provides location transparency, so a client can invoke methods on an object that resides remotely as if it were local. The ORB handles the details of remote communication, including marshaling and unmarshalling of data, method invocation, and return values, as well as exception propagation.

In CORBA, an ORB relies on an Interface Definition Language (IDL) to define the interfaces that objects expose. Client-side code uses stubs; server-side code uses skeletons. When a client invokes a method, the ORB marshals the request into a network message, sends it to the appropriate object, which then executes the operation and returns the result through the ORB to the client.

Key concepts include object references (IORs in CORBA), object adapters (such as the Portable Object Adapter), and ORB services like naming, trading, and security. ORBs come in various implementations (for example Orbix, TAO, JacORB, MICO) and aim to be language- and platform-neutral via IDL mappings that enable cross-language interoperability.

Historically, ORBs were central to CORBA and enterprise distributed systems in the 1990s and early 2000s. Over time, their prominence declined with the rise of web services, RESTful APIs, and modern RPC frameworks, though they remain in use in some long-lived systems and standards-based middleware.