2. 1 Distributed Systems Distributed Objects & Remote Invocation II (CORBA VS DCOM) Dr. Sunny Jeong. spjeong@uic.edu.hkspjeong@uic.edu.hk With Thanks to Prof. G. Coulouris, Prof. A.S. Tanenbaum and Prof. S.C Joo

3. 2 Distributed Object & Remote invocation % rmic 클래스명 desktop Local Data Format Global Data Format (ex, XDR, CDR, Java object serialization ) Local Data Format Marshalling Unmarshalling Marshalling Unmarshalling Network Request Reply

4. 3 Overviews  Distributed applications programming  distributed objects model(object-oriented model)  RMI invocation semantics(object-based model)  RPC(conventional procedure call model)  events and notifications(event-based programming model)  Products  Java RMI, CORBA, DCOM  Sun RPC  Jini( distributed event notification specification by Arnold K. – JVM)

5. About DCOM  DCOM is the distributed extension to COM (Component Object Model) that builds an object RPC layer to support remote objects.  A COM server can create object instances of multiple classes and also supports multiple interfaces allowing client- server communication.  A COM client interacts with a COM object by acquiring a pointer to the object ’ s interface and invoking methods through that pointer.  It is the product of Microsoft people.

6. About CORBA  CORBA (Common Object Request Broker Architecture), is a distributed object framework proposed by a consortium of nearly 800 companies called the Object Management Group (OMG) but developed by Sun people.  The core of CORBA is the Object Request Broker (OB) that acts as the object bus over which objects transparently interact with other objects located locally or remotely.  A CORBA object is represented by an interface with a set of methods and the instances are identified bye object reference  Object implementation interacts with the ORB through either an Object Adaptor or thru ORB interface.

7. FEATURES  Both DCOM and CORBA provide client-server type of communication.A client invokes a method implemented by a remote object (i.e., server).  The service provided by the server is encapsulated as an object and the interface of an object is described in an Interface Definition Language (IDL).

8. Features Cont ’ d  These interfaces serve as a contract between a server and its clients.  Some OOP features such as data encapsulation,polymorphism and single inheritance are present at the IDL level.  CORBA also support multiple inheritance but DCOM does not support. But DCOM can have multiple interfaces

9. Interaction Between Server & Client  The interaction between a client process and an object server are implemented as OO RPC style communications.

10. DCOM ARCHITECTURE

11. CORBA ARCHITECTURE

12. CORBA  Communication infrastructure for distributed objects  Allows a heterogeneous, distributed collection of objects to collaborate transparently

13. Basic CORBA Architecture Client Server ORB request response “Object Bus”

14. Interface Definition Language IDL  Interface Definition Language  Defines protocol to access objects  Like a contract  Well-specified  Language-independent

15. IDL Example module Calc { interface Adder { long add(in long x, in long y); }  Defines an object called Adder with a method called add

16. Stubs and Skeletons  Stub  lives on client  pretends to be remote object  Skeleton  lives on server  receives requests from stub  talks to true remote object  delivers response to stub

17. Stubs and Skeletons (Fig.) IIOP ORB Client Host Machine Client Object ORB Server Host Machine Stub Remote Object Skeleton

18. Execution Order  Compile IDL interface with idlj (-fall)  Compile files in the module folder  Compile server and client program  Run ORB demon (>start orbd –ORBInitialPort xxxx)  Execute application  (java servername-ORBInitialPort xxxx-ORBInitialHost localhost)  (java clientname-ORBInitialPort xxxx-ORBInitialHost localhost)