Comparison of Web Services, RMI, CORBA, DCOM Usha, Lecturer MCA Department of Computer Science and Engineering

Distributed object computing –Objects communicate (app2app) –Remote Procedure Call over network –Extension of OO programming The methods to build distributed systems/applications Two dimension: –Protocols –Data binding (or language mapping) Web Services(SOAP), RMI,CORBA, DCOM

Evaluate a System Architecture Interoperability –Different software and hardware on different machines from different vendors to share data Scalability –Adapt to increasing demand –Expand to thousands of nodes Usability –The ease to learn, to interpret the output Flexibility –The ease that the system can be modified and adapt to new requirements Accessibility, availability, affordability

Client Service Provider Web Server SOAP Dispatcher Service Objects Request Response SOAP UDDI Registry 1 2 3

RMI: Remote Method Invocation Client RMI Registry RMI Service Object 1 2 3

RMI (2) Protocol: Java Remote Method Protocol (JRMP) on the top of TCP/IP RMI Server: –Define an interface –Expose a set of methods RMI Client: –Lookup a server object reference in RMIRegistry –Invoke methods in the server object RMI Registry –Holds information about available server objects –Naming mechanism: URL

RMI(3) Between Server/Client –Java objects are serialized and transported Mobilized Code (Mobile agent) –Serialize object –transport the stream to the remote end –deserialize object –Execute code For JAVA only

CORBA: Common Object Request Broker Architecture

CORBA ORB (Object Request Broker): object bus –Find a CORBA object’s implementation –Prepare it to receive requests –Communicate requests to it –Carry the reply back to client CORBA server: has and interface and exposes a set of methods CORBA client: –acquires and object reference to a CORA server object –Make a method calls on the object reference

CORBA is a standard CORBA is a OMG’s standard IDL: Interface Definition Language Not tied to one language Transport: –GIOP (General Inter-Orb Protocol) –TCP/IP realization is called IIOP (Internet Inter- Orb Protocol).

DCOM: Distributed Component Object Model Protocol: Object Remote Procedure Call (ORPC) –On top of DEC’s RPC Server Object: –Multiple interfaces –Expose a set of methods Client Object: –Acquire a pointer to the server object’s interface –Call the exposed method

DCOM is COM on the wire Server object: –Memory layout: C++ vtable layout –Written in diverse programming languages lie C++, Java, VB, Object Pascal (Delphi), COBOL Require a platform supports COM services –Windows –Some companies provide products for UNIX, LINUX and mainframe

Web ServiceRMICORABDCOM Transport Protocol HttpJRMPIIOPORPC Data Binding XML schema (allow customized data type) Primitive, Serialized objects IDL (primitive and structure) MS IDL Compliant prog. Langs. Any (with XML parser, SOAP composition) javaAny (with IDL mapping standards) Many (C++, Java, VB, etc.)

Web Services RMICORABDCOM Interface Description WSDLInterface of server objects IDLMS IDL Remote Call By SOAP message Get references of server objects Get reference of server object Get Pointer of server objects RoutineStub Proxy DII Client: stub or proxy Server: skeleton Client: stub or proxy Server: skeleton Client: proxy Server: stub

Check against the Criteria Interoperability –Different software and hardware on different machines from different vendors to share data Scalability –Adapt to increasing demand –Expand to thousands of nodes Usability –The ease to learn, to interpret the output Flexibility –The ease that the system can be modified and adapt to new requirements Accessibility, availability, affordability