Common Object Request Broker Architecture
CORBA defines a model that specifies interoperability between distributed objects on a network in a way that is transparent to the programmer. It achieves this by defining ways for specifying the externally visible characterestics of a distributed object in a way that is implementation-independant.
This model is based on clients requesting the services from distributed objects or servers through a well-defined interface, by issuing requests to the objects in the form of events. An event carries information about an operation that needs to be performed including the object name (called an object reference) of the service provider and the actual parameters if any.
CORBA automatically handles a lot of network programming tasks such as object registration, object location, object activation, request demultiplexing, frame and error-handling, marshalling and operation dispatching.
CORBA objects are accessed through the use of an interface. OMG's Interface Definition Language (IDL for short) is used to define interfaces, their attributes, methods and parameters to those methods within the interface.
The central component of CORBA is the Object Request Broker (ORB for short). This component provides all the communication infrastructure needed to identify and locate objects, handle connection management and deliver data and request communication. One CORBA object never talks directly with another. Instead, the object requests for an interface to the ORB running on the local machine. The local ORB then passes the request to an ORB on the other machine. The remote ORB then locates the appropriate object and passes back an object reference to the requester.
The functions of the ORB are as follows:
Lookup and instantiate objects on remote machines Marshal parameters from one application object to the other Handle security issues across machine boundaries Retrieve and publish data on objects on local machine for another ORB to use Invoke methods on a remote object using static method invocation Invoke methods on a remote object using dynamic method invocation Automatically instantiate objects that are'nt currently running Route callback methods to the appropriate local object being managed Communicate with other ORBs using Internet Inter-ORB Protocol ( IIOP ) The other components that make up a CORBA application are Object Services, Application Interfaces, Domain Interfaces and Common Facilities.
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