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Distributed Objects & ComponentsCORBAPresented By :Mayuresh Wadekar (52)Ajay Yadav (53)

Distributed SystemDistributed System• Distributed System referred to computer networks where individualcomputers were physically distributed within some geographicalarea.Fig A. Difference Between Distributed & Parallel Computing

Distributed ObjectDistributed Object• Distributed objects refers to software modules that are designed towork together, but reside either in multiple computers connectedvia a network or in different processes inside the same computerFig B. Distributed objects residing in different machines.

Working of Distributed ObjectsWorking of Distributed ObjectsFig C. Working of Distributed Objects

Remote InvocationRemote InvocationFig D: Remote Invocation & Local Invocation

DISTRIBUTED OBJECTSDISTRIBUTED OBJECTS• Remote object references:Globally unique reference for a distributed objects maybe passed as a parameter.• Distributed actions:Initiated by a method invocation, potentially resulting ininvocation chains.• Distributed exceptions:Additional exceptions generated from the distributednature of the system, including message loss or processfailure

DISTRIBUTED OBJECTSDISTRIBUTED OBJECTS• Remote interfaces:Provides an abstract specification of the methods thatcan be invoked on the remote object.Fig D. Remote Interfaces

EVOLUTION OF DISTRIBUTED OBJECTSEVOLUTION OF DISTRIBUTED OBJECTS• Distributed objects as a natural evolution from threestrands of activity:1. Distributed systems:Earlier middleware was based on the client-server modeland there was a desire for more sophisticated programmingabstractions.2. Programming languages:Earlier work in object-oriented languages such as Simula-67and Smalltalk led to the emergence of more mainstream andheavily. Used programming languages such as Java and C++

EVOLUTION OF DISTRIBUTED OBJECTSEVOLUTION OF DISTRIBUTED OBJECTSFig E: OOP Distributed Objects3. Software engineering:In software engineering, significant progress was made inthe development of Object-oriented design methods, leading tothe emergence of the Unified Modeling Language

DISTRIBUTED OBJECT TECHNOLOGIESDISTRIBUTED OBJECT TECHNOLOGIES• DCOM:DCOM is used for single platform, multiple languages.• JINI:• CORBA:CORBA is use for Multiple platforms, multiple languages

CORBA(COMMON OBJECT REQUEST BROKERARCITECTURER)

INTRODUCTIONDefinition:• CORBA is a distributed object-based systems.• Provides inter-operability• CORBA is a middle ware neither 2-tier or 3-tierarchitecture.• CORBA is a technology to communicate 2 objectswhich are of heterogeneous type.• CORBA can be written in c, c++, COBOL and JAVA

• CORBA was created by OMG(Object managementgroup).• OMG was created in 1989.• OMG does not provide any s/w products.• The first version of CORBA was released in July ,1992as• “OBJECT MANAGEMENT ARCITECTURE GUIDE”• Concept of CORBA came from OLE.

CORBA ArchitectureCORBA ArchitectureORB coreDynamicInvocationIDLStubsORBInterfaceObjectAdapterStatic IDLSkeletonDynamicSkeletonClient Object ImplementationInterfaceRepositoryImplementatioRepository

ORBORB• Object Request Broker.• Gives the communication infrastructure that iscapable of relaying object requests acrossdistributed platforms.• Client calls the Object implementation throughinterfaces provided by ORB.• Advantages:• Separates Client and Server implementation• Separates both client and Server from underlyingcommunication infrastructure and protocol stack and soreplaceable while migration from one implementation toother

• In Java we cannot separate a class’s definitionfrom its implementations as we can in C++• CORBA allows the separation of definition andimplementation• CORBA uses IDL for defining interfaces betweenclients and servers• ORB Vendors provide specific IDL compilers forsupported languages– create target language stubs and skeletons forbuilding CORBA clients and servers• C, C++, Smalltalk, Java, COBOL …Interface Definition LanguageInterface Definition Language

Client StubsClient Stubs• Client side proxy for server.• Joins to the client at one end and to the ORBcore at the other end.• Client-to-stub interface is decided by thestandard OMG language mapping for thechosen programming language.• Clients actually invoke methods on stubobjects.

Server SkeletonsServer Skeletons• Acts as client proxy for serverimplementation.• Connects– to the server object via the mapping defined forits programming language on .– To the Object Adapter via a proprietary interface.• Invocation pass through Object Adapter toskeletons, which in turn actually invokemethods on server object.

Object AdapterObject Adapter• Different kind of object implementations -– objects residing in their own process and requiringactivation.– others not requiring activation.• OA helps the ORB to operate with differenttype of objects.• Most widely used OA - BOA (Basic OA)• Recently standardized - POA (Portable OA)

Interface RepositoryInterface Repository• Contains information regarding the interfaces to ORBobjects.• Can be used by the ORB in 2 ways -– To provide type-checking of request signatures, whether a requestwas issued through DII or stub.– To check correctness of inheritance graph.• Client objects can use it -– To manage installation and distribution of interface definitionsaround your network.– Language compilers may use them to generate stubs and skeletons.• Can be shared by more than one ORB or one ORB may referto more than one interface repository.

Implementation RepositoryImplementation Repository• Contains all the information regardingobject implementation.• Provides a persistent record of how toactivate and invoke operations on objectimplementations.• CORBA gives vendors free-hand in handlingimplementations.

• Generic interface for making remoteinvocations.• Uses interface repository at run-time todiscover interfaces.• No need of pre-compiled stubs.Dynamic Invocation InterfaceDynamic Invocation Interface

Dynamic Skeleton InterfaceDynamic Skeleton Interface• Allows the ORB and OA to deliver requeststo an object without the need of pre-compiled skeletons.• Implemented via a DIR (Dynamic InvocationRoutine).• ORB invokes DIR for every DSI request itmakes.

Differences between DynamicDifferences between Dynamicinvocation and static invocationinvocation and static invocation• Use• SI used for general purpose• DI used for special purpose where extra flexibility is needed• In SI interfaces should be known at compile time , In DIinterfaces are discovered during run time using data ininterface repository• Static Interface are easier to use and code

CORBA servicesCORBA services• Clock service maintains synchronized time• Authentication service validates user id’s• Object storage service: a file system for objects• Life cycle service: oversees activation,deactivation, storage, check pointing, etc.• Transactions and replication services• Naming services• Security services

CORBA Advantages:• Interaction with legacy systems.• Static and dynamic method invocations• High-level language bindings• Location transparency• Built-in security and transactions

• Design and process deficiencies.• Problems with Firewalls.• Problems with implementation.CORBA PROBLEMSCORBA PROBLEMS

RMI Vs CORBARMI Vs CORBA• Language Barrier.• RMI can be easier to master than corba.corbais rich and extensive family of std andinterfaces.• Corba is peer-to-peer orb communicationmodel and Rmi is server centric model.• RMI interface is defined in RMI-IIOP and corbainterfaces are defined in IDL.

• Distributed object can be used like a regular object,but from anywhere on the network• Creation, migration and deletion of distributedobjects is different from local objects• CORBA RMI is multi-language RMI• Distributed objects may be executed in parallel.CONCLUSIONCONCLUSION

REFERENCESREFERENCES[1]www.omg.org[2]www.corba.org[3]en.wikipedia.org/wiki/Distributed_object[4]George Coulouris, Jean Dollimore, Tim Kindberg, Gordon Blair,“Distributed Systems Concepts and Design”, Pearson Press[5] http://www.cs.wustl.edu/~schmidt/corba-overview.html

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