2. Introduction to CORBA Organizational Communications and Technologies Prithvi N. Rao H. John Heinz III School of Public Policy and Management Carnegie Mellon University

3. Readings Posting on the Class Web Site

4. Objectives Understand goals of distributed object technology Examine evolution of Software Bus Cite CORBA challenges Review OO support in CORBA

5. Seven Layer Model Revisited OSI ModelRevised Model Application Presentation Session Transport Network Data Link Physical Religion Politics Finance Environment Stacks Interfaces Substrates

6. Evolution of the Software Bus Remote MsgsRemote ProcedureDistributed Objects LPC IPC UDP/TCP DDE DLL OLE1.0 NCS RPC ONC RPC SHLRRBC ONC+ DCE OLE2.0DCOM CORBA/IIOP JAVA/RMI COM/CORBA

7. Terms Abbreviation Name Purpose LPC UDP TCP IPC SHL RRBC DDE DLL OLE 1.0 Local Procedure CallParameterized code segments User Datagram Protocol Intermachine messaging Transmission Control Protocol Reliable delivery of UDP messages Inter-process Communication Messaging between processes Shared Library/Object Dynamic Linking of shared code Release to release binary compat.Support for versioning of shared Libs. Dynamic data exchange uSoft’s messaging between procs. Dynamic Link LibraryuSoft’s shared library/object Object Linking and EmbeddingExtension of DDE for windows events

8. Terms Abbreviation Name Purpose COM DCOM RPC NCS RPC ONC RPC CORBA IIOP RMI SNMP Component Object ModelExtension DLL/C++ supporting versioning Distributed COMExtension of OLE2.0 supporting IPC Remote Procedure CallProxies making RPC look like LPC Network Computing Service Apollo’s inter-machine marshalling Open Network ComputingSun’s inter-machine marshalling Common Object Request Broker Architecture Extends NCS/DCE for dist. Object comm. Internet Inter-ORB ProtocolCORBA 2.0 standard marshalling protocol Remote Method InvocationDist. Java-java ipc marshalling protocol Simple Network Management Protocol Remote attribute query mechanism

9. Software Interconnect Bus Application Objects Common Facilities Services

10. Distributed Objects Objects +Remote Procedure Calls +Threaded Execution CORBA brings together three technologies

11. Why do we care? Interested in heterogeneous distributed application development Advanced complexity of applications Security Transactions Naming Open standard development

12. Distributed Objects: Combining Three Technologies Objects + Remote Procedure Calls + Threaded Execution Inheritance Encapsulation Polymorphism Distribution Heterogeneity Procedural Model Concurrency Priorities Pre-emption

13. The Basic Idea Take an Object Make it distributable Make it distributed

14. Terminology Distributed Objects and components are dispersed across processes that may exist on the same machine or located across machines on a network. Heterogeneous A pplication whose parts are located on machine that vary by hardware or by operating system or by programming language. Object-Oriented Applications written using objects.

15. CORBA Challenges Presents two challenges of developing distributed systems Making distributed application development no more difficult than developing centralized programs Providing an infrastructure to integrate application components into a distributed application Challenges are easier said than done due to: Partial failures Impact of latency Load balancing Event ordering

16. General ORB Structure CLIENT Object Implementation Object Request Broker Dynamic IIIDL StubsORB Interface IDL Skeleton Object Adapter Op(args)

17. CORBA Interface Definition Language (IDL) OMG IDL is an object-oriented interface definition language Used to specify interface containing methods and attributes OMG IDL support interface inheritance both single and multiple inheritance OMG IDL is designed to map onto multiple programming languages C, C++, Smalltalk, COBOL, Modula 3, DCE

18. OMG IDL Compiler OMG IDL compiler generates client stubs and server skeletons Stubs and skeletons automate the following activities in conjunction with the ORB Client proxy factories Parameter marshalling and unmarshalling Implementation class interface generation Object registration and activation Object location and binding

19. Requesting Service Using CORBA (and DCE) ClientServer Runtime System Application Code Client stub generated by IDL compiler Server Code Server stub generated by IDL compiler Runtime System

20. CORBA Services (OMG specified) Services essential for implementing objects Concurrency control service protects integrity of an object’s data when multiple requests to object are processed concurrently Event service that supports notification of interested parties when program-defined events occur Externalization service that supports conversion of object state to a form that can be transmitted between systems by means other than a request broker Life Cycle service that support creation, copying, moving and destruction of objects

21. CORBA Services (OMG specified) Naming service that permits object reference to be retrieved through associations between names and objects and for those associations to be created and destroyed Persistent Object service that supports persistence of an object’s state when the object is not active in memory and between application executions. Query service that supports operations on sets and collections of objects. Relationship services that provides for creating, deleting, navigating and managing relationships between objects Containment relationship between a “folder” object and “document” objects contained in that folder.

22. CORBA Services (OMG Specified) Transaction service provides support for ensuring that a computation consisting of one or more operations on one or more objects satisfies the requirements of: Atomicity in case of failure Isolation – transactions run concurrently but results are the same as if they ran serially Durability – result of successful transaction is never lost

23. CORBA Services (OMG specified) Security service that supports authentication, authorization, integrity and privacy to degrees and using mechanisms yet to be determined. Time service that provides synchronized clocks to all objects regardless of location. Collection service that support creation and manipulation of collections of objects. Replication service that would provide for the explicit replication of objects in a distributed environment for the purpose of fault tolerance and for management of consistency of replicated copies. Trader service that provides matchmaking service between clients seeking services and objects offering services

24. CORBA and Object Oriented Support Encapsulation Data and functions manipulating data are “encapsulated” in object. This enforces data hiding since the only way to access an object’s data is through the operations in the object’s public interface.

25. CORBA and Object Oriented Support Abstraction Abstraction of common features shared by objects in classes. A class definition describes the data associated with each instance of the class, defines the set of operations that can be invoked on an instance of the class and prescribes the functions that are executed in response to requests for those operations.

26. CORBA and Object Oriented Support Inheritance Inheritance of interfaces and implementations. This is the mechanism that supports the specialization or refinement of classes into subclasses. It is also one example of reuse inn object-oriented programming.

27. CORBA and Object Oriented Support Polymorphism Polymorphism is the ability for a request to specific operation to be handled differently depending on the type of object on which it is invoked. Example: subclasses of a common superclass may override functions defined by the superclass to differentiate how instances of the subclasses and superclass behave.

28. CORBA and Object Oriented Support Creation of new objects and classes Late binding of operation invocations to function calls allow programs to be written without regard for types objects they will manipulate

29. Summary Examined evolution of distributed object technology Introduced CORBA services Examined OO support in CORBA