1 eloadas corba 5

8/7/2019 1 Eloadas CORBA 5

1/29

Common Object Request

Broker Architecture(CORBA)

By:

Sunil GopinathDavid Watkins


2/29

Introduction

What is the purpose / goals of CORBA?

How to meet goals?

Example

Conclusion


3/29

What is the purpose / goals of CORBA?

Enable the building of plug and play

component software environment

Enable the development of portable, object

oriented, interoperable code that is

hardware, operating system, network, and

programming language independent


4/29

How to meet goals?

Interface Definition Language (IDL)

Object Request Broker (ORB)


5/29


Language Independence

Defines Object Interfaces

Hides underlying object implementation

Language mappings exist for C, C++, Java,

Cobol, Smalltalk, and Ada


6/29


module

{

interface [:inheritance]

{;

;

;

;

[] ()

[raises exception][context];

}

}

Defines a

CORBA object

Defines a

method

Defines a container

(namespace)


7/29

IDL Compiler

IDL

Definitions

IDL

Compiler

Stubs Skeletons

1. Define objects usingIDL

2. Run IDL file throughIDL compiler

3. Compiler uses languagemappings to generate

programming language

specific stubs andskeletons


8/29

Object Request Broker (ORB)

What is it?

Architecture

Request Handling

Scenario

CORBA Services CORBA Facilities


9/29

Application

What is it?

Implementation of CORBA specification

Middleware product

Conceptual Software Bus

Hides location and

implementation detailsabout objects

Hardware

OS Drivers

Middleware


10/29

Client / Object Interaction

Client Obj Impl

IDL IDL

ORB

Client Obj Impl

IDL IDL

ORB

Network

TCP

/IP

OSI

ATM

IPX

TCP

/IP

OSI

ATM

IPX


11/29

ORB Architecture

Interface

Repository

IDL

Compiler

Implementation

Repository

Client Object (servant)

ORB Core

IDLSkeleton

DSIORB

Interface

IDL

StubDII

OBJ

Ref

GIOP/IOOP

Object Adapter


12/29

Interface Repository

Interface

Repository

Object Adapter

Database of object definitions

Contains metadata about each object

Allows for introspection

Allows clients to discover interfaces at run-time Used in support of dynamic invocations


13/29

IDL Compiler

IDL

Compiler

Object Adapter

Compiles IDL definition into stubs andskeletons

Uses OMG specified language mappingsto translate IDL into a language specificimplementation


14/29

Implementation Repository

Implementation

Repository

Object Adapter

Contains information that allows the ORBto locate and activate objectimplementations

Provides information about the classes aserver supports, the objects that areinstantiated, and their IDs


15/29

ORB Core

ORB CoreGIOP/IOOP

Object Adapter

Provides mechanism for transparentlycommunicating client requests to target

object implementations Makes client requests appear to be local

procedure calls

GIOP General Inter-ORB Protocol

IIOP Internet Inter-ORB Protocol


16/29

ORB Interface

Client Object (servant)

ORB

InterfaceObject Adapter

Provides helper functions Converting object

references to strings

Creating argumentlists for requests made

through DII


17/29

IDL Stub

Static invocationinterface (SII)

Marshals applicationdata into a commonpacket-levelrepresentation

Network byte order(little-endian or big-endian)

Size of data types

Client

IDL

Stub


18/29

IDL Skeleton

Object (servant)

IDLSkeleton

Demarshals the

packet-level

representation backinto typed data that is

meaningful to an

applicationNetwork byte order

(little-endian or big-endian)

Size of data types


19/29

Dynamic Invocation Interface

Client

DII

Object Adapter

Dynamically issue requests to objects

without requiring IDL stubs to be

linked in

Clients discover interfaces at run-

time and learn how to call them

Steps:

1. Obtain interface name2. Obtain method description (from

interface repository)

3. Create argument list

4. Create request

5. Invoke request


20/29

Dynamic Skeleton Interface

Object (servant)

DSI

Object Adapter

Server side analogue to DII

Allows an ORB to deliverrequests to an object

implementation that does

not have compile-time

knowledge of the type ofobject it is implementing


21/29

Object Adapter

Object (servant)

IDLSkeleton

DSI

Object Adapter

Accept requests for service on behalf

of the servers objects

Demultiplexes requests to the correct

servant

Dispatches the appropriate operation

upcall on the servant

Registers classes it supports and their

run-time instances with theimplementation repository

Portable Object Adapter (POA)

policies control object behavior

(ie. LifespanPolicy)

Instance of the adapter design pattern


22/29

Object Reference

Client Object (servant)OBJRef

Object Adapter

Interoperable Object Reference (IOR)

Uniquely identifies each object Contents

Type Name (repository ID)

Protocol and Address Details

Object Key (object adaptor name, object name)


23/29

Request Handling

ORB POA

Server Application

Servants

POA

POA

Incoming

Request


24/29

Scenario

Interface

Repository

IDL

Compiler

Implementation

Repository

Client Object (servant)OBJRef

ORB CoreGIOP/IOOP

IDL

StubDII

Object Adapter

ORB

Interface

IDLSkeleton

DSI


25/29

CORBA Services

Provide basic infrastructure functionality

Currently there are 15 defined services

Naming - maps human names to object references(White Pages)

Event - provides both a push and pull event model

Object Trader - discover objects based on the services

they provide (Yellow Pages)

Transactions allows distributed objects to participate

in atomic transactions


26/29

CORBA Facilities

Provide higher-level functionality at the application

level

Provide standard components that can be used off-the-shelf

Two Categories

Horizontal user interface, information management,

systems management, and task management Vertical domain based, telecommunications, financial

services


27/29

Example


28/29

Conclusion

Distributed object, component architecture

Real world examples of design patterns

TAO freeware ORB

Adapter, Factory, Reactor, Strategy

Plugable Transports

CORBA Beans


29/29

References

www.omg.org

www.cs.wustl.edu/~schmidt/corba.html

http://www.infosys.tuwien.ac.at/Research/Corba/

OMG/arch2.htm

Communications of the ACM, October 1998

Jeri Edwards, Dan Harkey, and Robert Orfali.Instant CORBA. New York: Wiley Computer

Publishing, 1997.

1 eloadas corba 5

Documents