CORBA

  What is CORBA?

CORBA (Common Object Request Broker Architecture) is an object model, which provides an efficient and sophisticated architecture of distributed object computing. It makes message communications among remote objects on different machines transparent. Objects can be coded in different programming languages and running on different operation systems. This feature depends on a well-defined abstract language (IDL) for describing object interfaces in CORBA specification combined with a family of relative models and detail definitions. The first version of CORBA was released in 1991. The current version is 3.0 and is managed by the Object Management Group (OMG).

  What is Object Management Group (OMG)?

The Object Management Group (OMG), which also developed CORBA, is an international independent not-for-profit corporation. It was founded in April 1989 by eleven companies, including 3Com Corporation, American Airlines, Canon Inc. Data General, Hewlett-Packard, Philips Telecommunications N.V., Sun Microsystems and Unisys Corporation [1]. That same year, the OMG converted to a consortium with open membership. Currently there are over 800 companies with membership in the OMG. The mission of OMG is to provide a common framework for object-oriented application development through establishing industry guideline and detailed object management specifications. A lot of famous specifications, including UML, CORBA, OMA (Object Management architecture) are managed by this group. The OMG continually makes improvements to these specifications.

  What is Object Management Architecture(OMA)?

The OMG has developed a conceptual model, known as the core object model, and reference architecture, OMA. The OMG OMA attempts to define, at a high level of abstraction, the various facilities necessary for distributed object-oriented computing. The OMG OMA partitions the OMG problem to four parts, corresponding to four components in OMA, which are Object Request Broker (ORB), Object Services (OS), Common Facilities (CF), and Application Objects (AO). These components define the composition of objects and their interfaces. Objects are categorized into Object Services, Common Facilities, and Application Objects to establish the standardization strategy for the OMG. The core of the OMA is the Object Request Broker (ORB) which is a common communication bus for objects [2]. The technology adopted for ORBs is known as the Common Object Request Broker Architecture (CORBA) [2, 3, 4, and 5].

  The History of CORBA

The OMG released CORBA 1.0 in Oct, 1991, which is rough and only gave CORBA object model, Interface Definition Language (IDL), the API lib and interface factory of dynamic request management and dynamic invoking.

In Feb, 1992, the OMG released CORBA 1.1. This is the first wide-spread version, which removed a lot of contradictions existed in specification of CORBA1.0 and cleared some implicit concept in API and interface factory. The most important things are the Object Adapter concept is added into architecture with the interface of the Basic Object Adapter (BOA). The object adapter is the bridge between ORB and object instance. Its main functions are creating CORBA object and object application, identifying the request from client to CORBA object, classifying requests to different objects in server side and invoking CORBA object.

CORBA 1.2 came out in Dec, 1993, which only removed more contradictions in specification in pervious version.

In Aug. 1996, the OMG released CORBA 2.0, which made great improvement on interoperation, mostly because General Inter-ORB Protocol / Internet Inter-ORB Protocol (GIOP/IIOP ) were added in to solve the interoperation problem between CORBA platforms from different venders. Dynamic Frame Interface, extension of Object Interface Factory, support for multi-layer security and transaction service, the collaboration with OLE2/COM, mapping from IDL to C++ and Smalltalk were also added.

In Aug. 1997, the OMG released CORBA 2.1, which added mappings from IDL to Cobol and Ada, revised some context relative to interoperation and defined more types in IDL.

In Feb. 1998, the OMG released CORBA 2.2. An exciting new feature was Portable Object Adapter (POA), which gave an explicit standard specification about transformation between CORBA platforms from different venders. From the first version to CORBA 2.1, OMG only defined BOA, which provide the basic service for creating and implement a CORBA object. Unfortunately, during implementing the BOA, the ORB venders met a lot of problems OMG never noticed and found some contradictions in the BOA specification. So each vender used its specific techniques to solve these problems alone, which caused severe consequences. Applications developed for a certain CORBA platform were very hard to port to another platform. The goal of adding POA is to standardize some implementation methods to improve the transformability of CORBA. Mapping from IDL to Java and Collaboration between CORBA and DCOM (Distributed Common Object Model) were also added in this release.

In Jun, 1999, the OMG released CORBA 2.3, which provided some revisions on IDL/Java mapping, methods for collaboration between CORBA and DCOM and interoperation and security between ORBs

In late 2000, the OMG released CORBA 2.4.x, which includes several Quality of Service (QoS) specifications, which are intended for managing and selecting various underlying transport choices based on application needs. Specifically, this version contains the Asynchronous Messaging, Minimum CORBA, and Real-Time CORBA specifications as well as revisions made by several RTFs and FTFs, including those responsible for the Interoperable Name Service, Components, Notification Service, and Firewall specifications [6].

In end of 2001, the OMG will release CORBA 3.0, which will be a very important version in CORBA's history. In this version, CORBA will be completely integrated with the Internet and Java, support Quality of Service Control (QoS) and define new CORBAcomponents and CORBAscripting including a container environment that packages transactionality, security, and persistence, and provides interface and event resolution; Integration with Enterprise JavaBeans; A software distribution format that enables a CORBAcomponent software marketplace[6]. IDL will support Objects by Value. Other new features which have been already included in CORBA 2.4.x, such as Asynchronous Messaging, Minimum CORBA, Real-Time CORBA, Embedded CORBA, collaboration of DCE/CORBA, Firewall and Notification Service also will be combined with the new architecture smoothly. In these advanced techniques, Asynchronous Messaging, Objects by Values and CORBAcomponents are the most important changes in CORBA3.0. All of these changes will make the development and integration of huge information system applications possible [7].

  Download

CORBA Tutorial Slides [PDF][81K]

  Links

CORBA Introductory
Cetus Links: 18,838 Links on Components / CORBA

  Reference

1. The homepage of Object Management Group http://www.omg.org/news/about/index.htm

2. Zhonghua Yang and Keith Duddy, CORBA: A Platform for
   Distributed Object Computing? [PDF][298K]

3. Object Management Group. The Common Object Request
   Broker: Architecture and Specification (CORBA). Object
    Management Group (OMG), Framingham, MA., Revision
    1.2. Draft 29 December 1993

4. Object Management Group. The Common Object Request
   Broker: Architecture and Specification (Revision 2.0). Object
    Management Group (OMG), Framingham, MA., July 1995

5. Randy Otte, Paul Patrick, and Mark Roy. Understanding
   CORBA. Prentice-Hall, 1995. ISBN 0-13-459884-9

6. The homepage of OMG
   http://www.omg.org/
   technology/documents/formal/corbaiiop.htm

7. Liu Jinde, Su Lin, The new development of CORBA?
   computer world, 2000

8. The homepage of OMG
   http://www.omg.org/
   technology/corba/corba3releaseinfo.htm