CORBA 簡介

What is CORBA

Common Object Request Broker Architecture Specification of a Standard

Product of OMG(Object Management Group) Consortium 700+ companies Exception of Microsoft(Dcom)

  

Middleware

Definitions

  

  Distributed:Dispersed across processes   

  Hetrogeneous:Located on “different” machines   

  Object Oriented computing.

Motivation behind CORBA

  Platform and Language dependant software   

  Monolithic applications   

  Consumers and Developers are tied

Goal of CORBA

  Interoperability   

  Reusability   

  Portability

The CORBA ORB

  

  Responsible for the communication between applications   

  Middleware between servers and clients   

  Handles the “talking” between applications

REPRESENTATION OF CORBA

The Client

Object, Component or application

Make requests for services from servers

Can be a client for some requests and a server for

other requests

The Server(Object Implementation)

Provides a response to requests for services

Can be a server for some requests and a client for

other requests

The ORB core with IIOP(Internet Inter-Orb Protocol)

ORB core

Responsible for communicating requests

Identify and locate objects

Handle connection administration

Deliver Data

• ORB 可視為一種軟體的匯流排 (software bus)

• ORB 連接不同的物件，並隱藏了下列幾點：– 物件位置– 物件實作– 物件執行狀態– 物件通訊機制

• 各廠商只要遵循 ORB 對外的界面標準，至於內部可以由各廠商自行決定實作 ORB 的方法。

The ORB core with IIOP(Internet Inter-Orb Protocol)

IIOP developed by OMG

Handles communication between ORBs on TCP/IP

based networks

ORBs should support IIOP in order to be CORBA

compliant

The ORB core with IIOP(Internet Inter-Orb Protocol)

IIOP

IDL Client stubs

IDL(Interface Definition Language) CORBA definition of an Interface(object) Create Client stubs and server skeletons when compiled

IDL client stub A code written in IDL Use them 99.99% The other alternative is DII

Module <identifier>{ <type declarations>; <constant declarations>; <exception declarations>;

interface <identifier> [: <inheritance> ] { <type declarations>; <constant declarations>; <attribute declarations>; <exception declarations>;

[<op_type>] <identifier> ( <parameters> ) [raises exception] [context]; }

interface <identifier> [: <inheritance> ] :}

IDL(Interface Definition Language)

DII(Dynamic Invocation Interface)

The other alternative to invoke a server operation

Allow dynamic creation and invocation of requests to objects

The ORB Interface

Collection of operations that provides services to servers and

clients

The IDL server skeletons

Correspondant to client stub on the server side.   

Provides the means by wich a server’s operations can be

accessed   

Keeps the server from collapsing

The Dynamic Skeleton Interface (DSI)

  Corresponding to the DII on the server side.

The Dynamic Skeleton Interface (DSI)

  Corresponding to the DII on the server side.

Typical Client Method Call

Sequence of a method Call

1. Transforming the call into a request

2. Finding the server for the request

3. Preparing the server to receive the request

4. Communicating the data making up the request

5. Delivering the return reply

Transforming Method calls into requests

1. The client obtains an object reference for the server

2. The Client packages the reference,the method’s name & parameters and the type of return value

3. The Client executes the server’s method by calling the corresponding method in the Client stub

4. Inside the client stub the call is turned into a request

5. An ORB Interface operation is called to pass the request to the ORB

Finding the server for the request

1. ORB uses the information in the object reference to locate the server’s object

2. Determine the specific port number that the server object is accepting connections on

Preparing the server to receive the request

ORB sends a message to the

server’s Object adapter via the

IIOP   “Activate” the server

or

  ensure that it is already up and

running

Communicating the data making up th request

The client ORB sends the data

to the server’s ORB

   

The server skeleton turns the

data into a target language

specific method call

   

The server skeleton performs

the call on the server

implementation

Delivering the return reply

   

Changing the data back into

the client machine form

   

Send the data back to the

Client ORB and ultimately to

the Client stub

Object Management Architecture

Application Objects

Client Object Implementation

Common Object Services(COSS)

Common Facilities(CFA)

Object Request Broker (ORB)

Object Request Broker (ORB)