Distributed Systems - Guide to Cloud Computing for Business and Technology Managers - page 78

components are black boxes to the developer because the software developer
cannot see the implementation of the component, and the component can-
not be modified to perform services outside of those described in the IDL.
The behavior and properties of a component are specified by the IDL. If the
developer invokes an interface as described by the IDL, the specified behav-
ior from the component will be obtained. Interfaces of a component are like a
contract. They ensure that the component will perform according to the IDL,
regardless of how often it has been modified.
The biggest distinction between a component and an object is that an
object is not compatible with another object developed using different pro-
gramming languages. A programmer developing in Visual Basic could
not use an object created using C++. For a company like Microsoft, which
supports multiple programming languages, the incompatibility of objects
built using different programming language presents a problem in main-
taining object libraries. These libraries contain objects for commonly used
services and functions that help programmers in their application develop-
ment. Furthermore, the incompatibility of objects developed using different
programming languages presents a barrier to reuse for enterprises that use
multiple programming languages. Development efforts have to be spent rec-
reating an object developed in one programming language if that object is
needed for an application developed using another programming language.
In contrast, component standards were developed specifically to address
the issue that pieces of code developed using different languages cannot be
made to interoperate with one another. Software programs that adhere to
a component model will be able to interact with other components devel-
oped for the same model. The major component models are Common Object
Model (COM) and its derivatives, such as COM+ and Microsoft XML Web
Services platform (.NET), Enterprise JavaBeans (EJB), and Common Object
Request Broker Architecture (CORBA).
The basic idea behind this bird's-eye view of distributed com-
puting is that the concept of an object has moved from being a
technique for determining and building the components of an
application to a method for describing, encapsulating, assem-
bling, and managing entire applications in a distributed computing
environment. The original concept of an object could have been used to
define a Binary Tree Abstract Data Type (ADT) and its associated meth-
ods and how it would perform in a given application. The distributed
computing paradigm view of this object incorporates all of the original
definitions as well as requiring the interfaces and techniques by which
the Binary Tree ADT can have its methods and interfaces managed
remotely, whether it be via a JavaBean, an Object Request Broker (ORB),
or a COM component.