1. Copyright 1999 B.Ramamurthy
Introduction to CORBA
Copyright 1999 B.Ramamurthy
8/3/2019
B.Ramamurthy

2. Topics for Discussion What is CORBA? Object Request Broker (ORB)
Structure of a CORBA Application
Interoperability between ORBs
OMA (needed?)
OrbixWeb
Example1: Java Application (grid)
Example 2: Java Applet (grid)
Summary
8/3/2019
B.Ramamurthy

3. What is CORBA?
Common Object Request Broker Architecture (CORBA) specification (/standard) defines a framework for object-oriented distributed applications.
It is defined by a consortium of vendors under the direction of Object Management Group (OMG).
8/3/2019
B.Ramamurthy

4. What is CORBA? (contd.)
Allows distributed programs in different languages and different platforms to interact as though they were in a single programming language on one computer.
Brings advantages of OO to distributed systems.
Allows you design a distributed application as a set of cooperating objects and to reuse existing objects.
8/3/2019
B.Ramamurthy

5. Object Request Broker (ORB)
A software component that mediates transfer of messages from a program to an object located on a remote host.
Hides underlying network communications from a programmer.
ORB allows you to create software objects whose member functions can be invoked by client programs located anywhere.
A server program contains instances of CORBA objects.
8/3/2019
B.Ramamurthy

6. Clients, severs and objects
Server0
Client
CORBA Object
invocation
Server1
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B.Ramamurthy

7. CORBA Objects and IDL
These are standard software objects implemented in any supported language including Java, C++ and Smalltalk.
Each CORBA object has a clearly defined interface specified in CORBA interface definition language (IDL).
The interface definition specifies the member functions available to the client without any assumption about the implementation of the object.
8/3/2019
B.Ramamurthy

8. Client and IDL
To call a member function on a CORBA object the client needs only the object’s IDL.
Client need not know the object’s implementation, location or operating system on which the object runs.
8/3/2019
B.Ramamurthy

9. IDL facilitates internetworking
-- Specify in IDL
-- Use IDL-language compiler
-- Client sees only IDL interface
C++
Java
target object
smalltalk
OLE
(VB, PB,Delphi)
Ada, Cobol etc.
8/3/2019
B.Ramamurthy

10. Separation of Interface and Implementation
Interface and implementation can be in two different languages.
Interface abstracts and protects details (trade secrets) from client
Interface offers a means of expressing design without worrying about implementation.
8/3/2019
B.Ramamurthy

11. ORB : Conceptual View
When a client invokes a member function on a CORBA object, the ORB intercepts the function call.
ORB directs the function call across the network to the target object.
The ORB then collects the results from the function call returns these to the function call.
8/3/2019
B.Ramamurthy

12. Implementation Details
Client
ORB
Object
Stub
Access to the services provided by an Object
ORB : (Object-oriented middleware) Object Request Broker
ORB mediates transfer between client program and server object.
8/3/2019
B.Ramamurthy

13. CORBA Application Development
1. Define interfaces to the objects in your system using CORBA IDL.
2. Compile these using IDL compiler : this compiler is language specific.
IDL - Java compiler generates Java code from IDL definitions.
This Java code contains client stub code which allows client code development and
A skeleton code which allows implementation of server object code.
8/3/2019
B.Ramamurthy

14. CORBA Application Development (contd.)
3. Implement client, server code in Java (or what ever language).
4. Compile client.java, server.java and all the other source files generated by IDL compiler. (javac)
5. Register the server (object) with the ORB Implementation Repository.
6. Run CORBA (Ex: OrbixWeb) daemon, the server (if needed) and the client.(java)
8/3/2019
B.Ramamurthy

15. Example 1: Two-dimensional Grid
A grid is an abstract view of a number of commonly used components such as spreadsheets or relational (database) tables.
8/3/2019
B.Ramamurthy

16. Defining the IDL Interface
// In file grid.idl
interface Grid {
readonly attribute short height;
readonly aatribute short width;
void set (in short row, in short col, in long value);
long get (in short row, in short col); };
8/3/2019
B.Ramamurthy

17. Overview of Compilation Process
Grid.idl
IDL Compiler
_GridStub
_GridSkeleton
Classes &
interfaces
Grid server
application
Grid client
application
Java compiler
Server byte
code
Client byte
code
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B.Ramamurthy

18. Summary We introduced general operation of CORBA.
Also details of specifying a client, server application, compiling them and registering and running.
In the next class we will look at actual implementation of CORBA client-server application.
8/3/2019
B.Ramamurthy