Lesson 6	Distributed object middleware
Objective	Describe the function of distributed object middleware.

What is Distributed Object Middleware?

Distributed object middleware is middleware that provides a deployment, execution, and management framework for objects hosted on different computing environments. The chief difference between object-oriented and RPC-based middleware is that it's object-oriented, which provides for far greater design and deployment flexibility, and reuse.

How does distributed object middleware work?

The kernel of distributed object middleware is the object request broker (ORB). This FlipBook illustrates how the ORB works.

1) Orb 1

2) Orb 2

3) Orb 3

4) Orb 4

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ORB Function Corba

In sum, distributed object middleware allows objects from applications developed in different languages, running on different physical computing environments, to interoperate and share methods in a flexible and dependable fashion.

Distributed object middleware Considerations

Consideration

Explanation

Difficult to develop

Very few programmers are well-versed in the IDL (interface definition language) required for most ORB implementations. In addition,since this type of approach mediates different languages between different computing environments, this kind of middleware isconceptually difficult to design. Few corporate IT departments possess considerable ORB and IDL expertise, and therefore must dependon typically expensive third-party help.

Components and Standards

Consider using component and object architectures, such as Enterprise Java Beans (EJBs) or ActiveX that can be extended through distributed object standards like CORBA and COM+. Though relatively few eBusiness solutions actively use distributed objects at this time, plenty of eBusiness solutions take advantage of component and object standards.

Enterprise Java Beans (EJB): Component software architecture from Sun that is used to build Java applications that run in the server. It uses a "container" layer that provides common functions such as security and transaction support and delivers a consistent interface to the applications regardless of the type of server. CORBA is the infrastructure for EJBs, and at the wire level, EJBs look like CORBA components. EJBs are the backbone of Sun's J2EE platform, which provides a pure Java environment for developing and running Web-based applications.
ActiveX: A set of rules for how applications should share information. This is Microsoft's version of Java applets.
CORBA: Enables pieces of programs, called objects, to communicate with one another regardless of what operating system they are running on or what programming language they were written in.
COM+: Microsoft's language independent component architecture intended to provide general purpose, object oriented means to encapsulate commonly used features and functions.

The next lesson is about yet another kind of middleware--transaction processors.

Distributed Object Middleware - Quiz

Click the Quiz link below to review the peculiarities and functions of distributed object middleware.
Distributed Object Middleware - Quiz

Object request broker: A program that controls communication between clients and objects on servers.