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CORBA

CORBA. Alegria Baquero. Introduction. CORBA  C ommon O bject R equest B roker A rchitecture A project of Object Management Group (OMG) CORBA is an OO distributed communication middleware Mediates the communication between distributed objects

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CORBA

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  1. CORBA Alegria Baquero

  2. Introduction • CORBA  Common Object Request Broker Architecture • A project of Object Management Group (OMG) • CORBA is an OO distributed communication middleware • Mediates the communication between distributed objects • ORB  the object-oriented version of a RPC

  3. What is CORBA for? • Invoking methods on objects in a local or remote host (in the same or in different machines) • Make autonomous applications communicate with each other • Connects objects across a network • Objects can live on different platforms (OS)

  4. CORBA and component heterogeneity • Objects can be written in different languages • Mappings available for many languages

  5. What are CORBA’s strengths? • Simplifies programming of distributed systems • Can support a large number of clients invoking an object method • Location transparency • It is not necessary to know in what language an object or CORBA service is written

  6. What are CORBA’s strengths? • Easy integration with other technologies (e.g. legacy systems) • Wide platform and language support • Scalability  able to manage an unlimited number of objects • Efficient transmission over the network by converting programming language to a binary buffer

  7. CORBA in more detail • No strict differentiation between client and server. A computer can be both client and server. • Client  calls object; Server  contains object • Every object instance has a unique reference to be able to communicate with it. • IOR (Interoperable Object Reference)  a common format for object references exchanged over IIOP

  8. CORBA in more detail • It a synchronous way of communication • CORBA has a collection of services (libraries) that provide functionality to extend basic CORBA • Uses the Internet Inter-ORB Protocol (IIOP) for distributed programs to communicate over the internet.

  9. The architectural style • The constraints that CORBA enforces belong to the “distributed objects” architectural style • Distributed objects is a mix of object-oriented style with client-server style • One of these constraints is the serialization of parameters for an effective communication

  10. GIOP (General Inter-ORB Protocol) IIOP (Internet Inter-ORB Protocol) • Protocol by which ORBs communicate • IIOP is a GIOP specific for TCP/IP communication GIOP + TCP/IP = IIOP • Common misconception  IIOP is something separate that the developer needs to write. An ORB already incorporates IIOP • IIOP  defines a set of data formatting rules  Common Data Representation (CDR)

  11. GIOP (General Inter-ORB Protocol) IIOP (Internet Inter-ORB Protocol) • CDR  tailored to the data types supported in the CORBA Interface Definition Language • With CDR  IIOP defines a set of message types that support ORB semantics defined in the CORBA core specification

  12. What is an IDL and what is it for? • Interface Description Language  a specification language to describe component’s interfaces • Defines the public application programming interface (API) to access objects in a server • For each object an IDL interface is defined, and it represents a contract to invoke methods on the object • IDL is language independent, but can be mapped to many languages like C, C++ or Java • An IDL compiler translates IDL into the equivalent in the chosen programming language

  13. where does IDL stand...

  14. more on IDL… • IDL language-independence enables interoperability and transparency • An IDL interface can include operations and attributes (getters and setters) • IDL code is compiled into client stubs and object skeletons which serve as proxies (acting in behalf of something) • Stubs and skeletons are as well created by the IDL compiler

  15. more on IDL… • Skeleton  receives incoming requests and translates to the application domain • When a method is called on the object, the calling parameters are serialized (transformed into binary data) to cross the network. • To create an object in a different server, the client needs to invoke a function in the server which creates the object. • How to reference an object? A “naming service” maintains a directory of objects to call the up by name. • The skeleton receives it, rebuilds the request and makes the call on the object. • Strong data type system to prevent errors.

  16. Java RMI • RMI  Remote Method Invocation • Is an alternative option to using IDL • Uses also IIOP to implement a CORBA

  17. Portable Object Adapter (POA) • Is a mechanism to connect a request with to the code to process it • Is a standard component defined by the CORBA specification • Goal  build objects that can be supported in different ORBs • Assists an ORB in delivering client requests to server object implementations (servants) • Generates and interprets object references • Portability achieved by standardizing skeletons classes that are generated by the IDL compiler • Deactivates idle objects' servants; activates them when needed

  18. ORB vendors • Orbix (IONA)  Enterprise CORBA • Orbacus (IONA)  small footprint, embeddable CORBA • Visibroker (Borland)  for Java, C++, C#. • MICO (ObjectSecurity)  available as GNU open source software • ORBexpress (Objective Interface Systems)  a real-time ORB • ORBit (GNOME) for C, C++ and Python • OmniORB for C++ and Python • opalORB for Perl • JacORB for Java • OmniBroker  for non-commercial use. C++ and Java

  19. References • www.omg.org • Common Object Request Broker Archictecture, OMG, July, 1995. • www.wikipedia.org • http://www.ciaranmchale.com/corba-explained-simply/ • Taylor et. al. (2008). Software Architectures: Foundations, Theory and Practice. • java.sun.com • Pyarali, I. (1998). An overview of the CORBA portable object adapter. StandardView, 6(1), 30-.

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