Distributed systems corba remote connection

Common Object
Request Broker
Architecture…
…taking objects a step further!

• Rapid changes in HW and OS lead to advantages
of client/server systems
• Result: greater system complexity, user demand,
management expectations
• Additional pressure from the necessity to
maintain legacy systems

Object Management Group,
(OMG) formed in 1989
Focus on integration of systems and
applications across heterogeneous platforms
After soliciting input,
CORBA standard was
defined and introduced
in 1991

PROVIDES HIGH-LEVEL OBJECT
ORIENTED INTERFACE!!!
The only REAL competitor is, of course…
…MICROSOFT DCOM

…allows applications and their objects to
communicate with each other no matter
where they are and or who designed them!!

• When introduced in 1991, CORBA defined the Interface
Design Language, (IDL), and Application Programming
Interface, (API)
• These allow client/server interaction within a specific
implementation of an Object Request Broker, (ORB)
CLIENT
SERVER/OBJECT
IMPLEMENTATION
ORB
request
ORB
Result/
error

A technology independent
syntax for describing object
encapsulation
<specification> ::= <definition>+
<definition> ::= <type_dcl> “;”
| <const_dcl> “;”
| <except_dcl> “;”
| <interface> “;”
| <module> “;”
An example of the
syntax

The first thing we must do is define the
interface to the serving object in OMG
IDL:
#ifndef _HELLOWORLD_IDL
#define _HELLOWORLD_IDL
module HelloWorld {
interface SimpleHelloWorld {
string sayHello();
};
};
#endif
import HelloWorld.*;
public class HelloWorldImpl
implements SimpleHelloWorldServant{
private final java.lang.String
myString = "Hello World!";
public synchronized
java.lang.String sayHello()
throws
sunw.corba.SystemException
{
return myString;
}
}
…it even has its own “hello world”!!

ORB is “middleware”
Based on client/server model of distributed
computing, CORBA inserts a “broker”
between client and server
CLIENT
SERVER/OBJECT
IMPLEMENTATION
ORB
request
ORB
Result/
error

Broker provides basic messaging and
communication between client and server,
“insulating” applications from the specifics of
the system configuration
Client “transparently” invokes
methods on server, either on same
machine or across network

The ORB :
• intercepts calls
• finds object
• invokes method
• passes parameters
• returns results or error messages
REGARDLESS OF THE OBJECTS
LOCATION, ITS PROGRAMMING
LANGUAGE OR EVEN THE OPERATING
SYSTEMS INVOLVED!!

IDL generates ‘stubs’ and ‘skeleton’ programs for each interface
‘Stub’ acts like a local function call, providing interface to ORB
‘Skeleton’ is server side implementation of IDL interface
Application software
client Object implementation
Object Request Broker, (ORB)
stub DLL
Object
Adapter
adapter
skeleton

Application software
client Object implementation
Object Request Broker, (ORB)
stub DLL
Object
Adapter
adapter
skeleton
Skeletons and stubs…
…return the results and error messages

The role of CORBA and the ORB are defined in the
Object Management Architecture
Application
objects
CORBAdomains CORBAfacilities
Object Request Broker
CORBAservices
Included within the OMA are four object
categories:

The four categories of the OMA:
• CORBAservices: creation/movement of objects,
queries/transactions, concurrency control, directory
servi ces
• CORBAdomains are ‘vertical market’ standards. For example:
financial, medical, telecommunications and manufacturing
• CORBAfacilities include compound document and system
management. Both can be applied across multiple vertical
domains for added functionality
• Applications: user defined and proprietary interfaces

The result?
• Programmer free to design system as they see fit, ORB defines
application protocol via IDL
• ORB allows integration of existing components into
a network object architecture
• now possible to integrate existing systems with off-the-
shelf products
…represents the next step in software
re-use
• Programmer free to choose language, environment and OS

Distributed systems corba remote connection

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