Distributed Systems - Guide to Cloud Computing for Business and Technology Managers - page 82

With the growth of the Web, the search soon started for a Web compliant
replacement for this technology. In Chapter 8, we will see that Web Services
are currently the most natural solution to develop distributed systems on
the Web.
3.2.2.1 Component Object Request Broker Architecture (CORBA)
In 1989, a group of eight companies formed the Object Management Group
(OMG) to promote the use of object technology and create standards for
object interoperability. OMG introduced CORBA 1.0 in 1991 as the first
vendor-independent object standard. What CORBA 1.0 brought was the IDL
and a set of application programming interfaces (API) that allow objects to
request and receive services from other objects. CORBA is programming
language independent and platform neutral. As long as vendors develop
programs following CORBA standards, their programs can interoperate
with other CORBA-compliant programs. The platform neutral feature of
CORBA means that CORBA-compliant programs can be executed by any
platform with CORBA middleware. The CORBA standards have under-
gone several revisions to include a component model, support for transac-
tions, a bridge to the component models (EJB and COM), and support for
messaging service (such as Message Queuing [JMS]). Using CORBA stan-
dards, vendors have introduced middleware products to support CORBA
components.
The central building blocks of CORBA are the object request broker or
(ORB), IDL, dynamic invocation interface (DII), interface repository, and
object adopter (OA). The ORB is the heart of the CORBA architecture. It
serves as the middleware for object-based integration, similar to what RPC
does for procedural programs. A client application can invoke a method
through the ORB without worrying about the system platform, network con-
nectivity, or object implementation details. A method in the object-oriented
world is equivalent to a procedure in the procedural world. Methods are
functions that an object has exposed to the outside world. In the compo-
nent world, an object method could become a component interface. The cli-
ent application sends a request to the ORB. The ORB delivers the request
to the requested object, whether residing in a remote server or on the same
server. Once the request has been processed, the ORB returns the results to
the calling application. The ORB hides all of these concerns from the client
application. To the client application, the method it is invoking appears to
be implemented in the same platform and using the same programming lan-
guage, even if the method might belong to a program executed on a different
platform and constructed in a procedural language. The ORB abstracts all
of these details to put the client and the invoked object on the same playing
field. Every implementation of a CORBA ORB supports an interface reposi-
tory. The client simply has to invoke an object using the interface definition
stored in the interface repository.