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CORBA

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IntroductionCORBA (Common Object RequestBroker Architecture) is a standard thatenables an object written in one

programming language, running on oneplatform to interact with objects acrossthe network that are written in otherprogramming languages and running onother platforms.

For example, a client object written inC++ and running under Windows cancommunicate with an object on a remotemachine written in Java running under

UNIX.

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OMGThe CORBA specification was developedby the Object Management Group(OMG).

The OMG is an international, not-for-profit group consisting of approximately800 companies and organizationsdefining standards for distributed objectcomputing

CORBA is only one of the specificationsthey develop. They are also behind otherkey object oriented standards such asUML (Unified Modeling Language).

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HistoryThe OMG was established in 1988 andthe initial CORBA specification came outin 1992. Over the past 10 years

significant revisions have taken place.

Version 2.0, which defined a commonprotocol for specifying howimplementations from different vendorscan communicate, was released in the

mid-nineties.

The current version of CORBA is 3.0,which introduced the CORBAComponent Model.

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TodayToday, CORBA serves as middleware fora variety of large enterprise levelapplications.

One of the most important and mostfrequent uses is for servers that musthandle a large number of clients, at highhit rates, with high reliability.

The current users of CORBA are diverse- including The Weather Channel,GNOME, US Army, CNN, and CharlesSchwab.

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CORBA IntegrationsAn implementation of CORBA has beenintegrated into Netscape browsers.

CORBA has been built into Netscape

ONE (Open Network Environment) -Netscapes application environmentbased on open internet standards.

The Enterprise Edition of IBMs

WebSphere (a software platform to helpbuild and deploy high performance websites) integrates CORBA (as well asEnterprise Java Beans) to build highlytransactional, high-volume e-business

applications

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CORBACORBAArchitecture

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Three-tierCORBAArchitecture

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The Primary Elements IDL

Interface Definition Language

Client / Server CORBA Objects Abstract objects based upon a concrete

implementation

ORBs

Object Request Brokers GIOP / IIOP

General and Internet Inter-Object

Protocols

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Interface Definition Language Defines public interface for any

CORBA server.

C++ like syntax

Client and Server implemented

based on compilation of the same

IDL (usually)

OMG has defined mappings for: C, C++, Java, COBOL, Smalltalk, ADA, Lisp,

Python, and IDLscript

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Highlighted IDL Features

Pass by reference and by value

In, out, and inout parameters

Inheritance

Throwing of exceptions

The Any Type

Callbacks

Enables Peer-to-Peer Object

Communication. Also supports:

structs, unions, enumerations, all c++scalars, arrays, sequences, octets,strings, constants, and typedefs.

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Steps to Write a CORBAObject

in Java

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Client / ServerCORBAObjects

CORBA OBJECT

(abstract)

Implementation Object

(CORBA enabled)

Member Object

Local Server

Object

Local Server

Object

Implementation

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Client / ServerCORBAObjectsCont.

Abstract Do not have their own implementation. The

elements of a CORBA object (interface,implementation, and location) are heldrendered via other elements.

Implemented via a Servant A servant is a block of code (usually an

instance of a class) which implements thepublic interface of the CORBA object.Depending on the server policies, there mayor may not be multiple instances of the

servant and it may or may not be multi-threaded.

Configured in code or at server startup Unlike COM+ and EJB the policies for a

CORBA object which control things such as

Security, threading, and persistence are notconsole configurable

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Object Request Brokers

(Orbs) Responsible for all communication

Locating objects

Implementation specific

Known IOR(Inter-Object Reference) Naming and Trading Services( DSN-like)

Transferring invocations and returnvalues

Notifying other ORBs of hosted Objects

Must be able to communicate IDLinvocations via IIOP

If an ORB is OMG compliant, then it isinteroperable with all other OMGcompliant ORBs

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AdditionalORBServices

Interface Repository

A Database of all of the IDL for compiled

objects running on the ORB Implementation Repository

A Database containing policy information

and the implementation details for the

CORBA objects running on the ORB

Load Balancing

Fail-over support

Security

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Drawbacks

Lower Level than COM+/.NET/EJB

Configuration in Code

Steeper Learning Curve than other

solutions.

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Object Management

Architecture(OMA) Center of all the activity

undertaken by OMG

OMA specifies a range ofarchitectural entities surroundingthe core ORB, which is CORBAproper

Detailed specifications for eachcomponent and interface categoryis populated in OMA referenceModel

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OMAReferenceModel

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CORBAServices

CORBA Services provides basic

functionality, similar to the services

that system library calls do inUNIX. Functions includes creating

objects, controlling access to

objects, keeping track of relocated

objects and to consistentlymaintain relationship between

objects.

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HorizontalCORBA

Facilities Horizontal CORBA Facilities sit

between the CORBA services and

Application objects.T

hesecomponents providing supportacross an enterprise and acrossbusiness. Four facilities: thePrinting Facilities, the Secure Time

Facilities, the InternationalizationFacilities, and Mobile AgentFacilities.

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Domain(Vertical) CORBA

Facilities Domain CORBA Facilities are the

most exciting work at OMG. Define

a standard interfaces for standardobjects shared by companies

within a specific vertical

market(e.g. healthcare,

manufacturing, finance). Now nineindustries have their own OMG

task force.

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Application Objects

Topmost part of the OMA hierarchy.

Provide access to application objects

that can invoke methods on remoteobjects through ORB. Application is built

from a large number of basic object

classes, new classes can be generated

or specified provided by CORBA

services. Standardization is not required.

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ThreeBenefits of using

OMA1. Coding is quicker, so application

can be deployed sooner

2. Applications designed arounddiscrete services have better

architecture

3. Many OMA implementations have

enterprise characteristics built in:

theyre robust, and they scale

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CORBA vs. DCOM

DCOM supports an object-

oriented model, but differs

substantially from classical OOmodels. DCOM object provides

services through one or more

distinct interfaces.

DCOM is lack of polymorphism,instead, it constructs application

from binary components.

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CORBA vs. DCOM

The major difference is CORBA is an

open specification. DCOM has the

potential to evolve at a faster rate than

CORBA because the politics will be

simpler.

CORBA can be deployed far more widely

than DCOM and runs in most current OS

environment, while DCOM is runningalmost exclusively in the Windows

environment.

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CORBA vs. JAVA/RMI

Some overlap between these two,

both provide a viable means of

building distributed applications. CORBA is concerned with

interfaces between objects and

applications modeled as objects,

Java is primarily concerned withthe implementation of these

objects.

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CORBA vs. JAVA/RMI

JAVA/RMI systems fall short ofseamless integration because of

their interoperability requirementswith other languages. JAVA/RMIsystem assumes thehomogeneous environment of theJVM, which can only take

advantage of Java Object Model. Coexistence between CORBA and

Java

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The Future ofCORBA

Much easier for developers to build and

run client/server applications written in

different languages using the IDL

interface

Compute-domain benefits

Functionality the same as if written to

sockets or some other RPC device

Business-domain benefits

Allows rapid development of full service

website

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Compute-DomainEnhancements

in traditionalbusiness Remote access to all network

systems for employees.

product descriptions pricing

stock

order placement

customer credit data

Business works smarter, notharder

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Business-DomainEnhancementsfore-business

Builds on compute-domain work

add web functionality to existing internal

network uses CORBAs IDL to integrate new

processes

Development and maintenance ofcustomer centered e-commerce site is

still manageable for IT department. Gives business time to sell product, not

fix problems

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Companies UsingCORBAToday AT&T

Late 1990s developed 20 to 40 systemsusing CORBA for both internal andexternal access

Are certain development time for futureprojects will be greatly reduced bybuilding reusable frameworks with theOMG

The Weather Channel Used CORBA and Linux

System is reliable, low maintenance,offers data logging

Cut software development time frommonths to weeks

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Companies UsingCORBA

Today

Raytheon Company

Needed to update its complex real-time

distributed system

Built new system using C++ and CORBA

Ready to build next generation system

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Companies with Plans to

Develop UsingCORBA Chase Manhattan Bank

Plans to develop wholesale banking service

Will use CORBA and Java-based middleware

Further plans to introduce Java-basedmortgage application service as well asintegration with third-party applicationspossibly by years end

Nokia Telecommunications Combining use of Orbix and CORBA to

continue enhancing products and managevalue added services based on a commonarchitecture.

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NOKIA

Nokias decision [to use CORBA]

highlights the continuing adoption of

CORBA and is recognition of the fast,

effective, scaleable and open approach

to the development of powerful,

intelligent, mission-critical network

services that CORBA offers.

Colin Newman, VP Marketing at IONA

(Developers of the Orbix ORB)

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References

www.oma.org

www.corba.org

developer.java.sun.com/developer/

onlineTraining/corba