A Preview of CORBA 3

Management Group has been the most influential standard in the OO world and one of the principal steps in the indus-try's move to component-based development. Jon Siegel, Director of Domain Technology at the OMG and best-selling CORBA book author, gives us a preview of CORBA 3, the next step in the technology. —Bertrand Meyer C ORBA 3, the first major addition to CORBA from the OMG since the Internet Inter-ORB Protocol (IIOP) added interop-erability in 1996, will be released very soon. In all, OMG specifications work at three levels: The Unified Modeling Language (UML) standardizes model representation in OO analysis and design; CORBA defines an interoperability infrastructure ; and the Object Management Architecture (OMA) standardizes interfaces for services and facilities used in distributed applications from near system level (Naming and Event Services, for example) to application level (such as the Currency Object in finance, and the Patient or Person Identifier facility in health care). I only have room to discuss CORBA in this column. For information on the rest, or to download any of the free OMG specifications, visit In CORBA, programmers define their objects' interfaces in OMG Interface Definition Language (IDL), which is also an international standard (ISO/IEC 14750 and ITU-T Recommendation X.920). When you write an interface definition , you specify the operations the object is prepared to perform, the input and output parameters each requires, and any exceptions that may be generated along the way. This interface constitutes a contract with clients of the object, who use the same interface definition to build and dispatch invocations the object implementation uses to receive them and respond. This design provides great flexibility and has many benefits. It enforces encapsulation and allows clients to access object implementations independent of each other's programming language, OS, hardware platform, data representation, location on the network, and native protocol. You can write your CORBA clients and objects in most standard languages. For six programming languages (soon to be seven), an OMG standard language mapping specifies how OMG IDL types and method invocations convert into language types and function calls or invo-cations. IDL compilers use the mappings to generate function or method calls. for Lisp is being adopted. Not-yet-standard mappings are available now for objective C, Visual Basic, Perl, and other languages. Figure 1 shows a request passing from a client to an object implementation in the CORBA architecture. Two aspects of this architecture stand …