Keith Duddy

CORBA: a platform for distributed object computing

Distributed computing has made significant advances in the past few years as witnessed by the release of OSFs Distributed Computing Environment (DCE) and the adoption of a set of specifications for distributed object computing by the Object Management Group (OMG). In this report, we discuss OMGs work in distributed computing based on object technology. We attempt to provide a comprehensive coverage of OMGs technology, including an overview of Object Management Architecture, the rationale behind OMGs work, a technical tour of CORBA, and an overview of Object Services and Common Facilities. A technical comparison between DCE and CORBA is provided. User perspective and the future potential of OMGs technology are discussed in the conclusion. 1 I n t r o d u c t i o n The Object Management Group (OMG) is an international industry consortium that promotes the theory and practice of object oriented ( 0 0 ) software development. Their goal is to provide a common architectural framework, across heterogeneous hardware platforms and operating systems, for inter-communication of application objects. The adoption of an object-oriented approach is motivated by the desire for software development with reusable components that interact with one another through well defined interfaces. Industry trends indicate that object technology is gaining wide acceptance, with most vendors now providing tools and environments to support OO software development. Just as structured modular programming became standard software engineering practice in the 1980s it is anticipated that this will give way to a dominance of the object-oriented paradigm within a few years. The OMG was founded in May 1989, by eight companies: 3Corn Corporation, American Airlines, Canon Inc., Data General, Hewlett-Packard, Philips Telecommunications N.V., Sun Microsystems and Unisys Corporation. The OMG began independent operations as a non-profit corporation in October 1989 [8]. It now boasts over 500 member companies internationally, with almost every significant computer vendor represented. The organisation performs no development work, relying rather on existing technologies offered by member companies. Its approach is to issue Requests for Proposals (RFPs) on all aspects of

Processes, roles, and events: UML concepts for enterprise architecture

This paper presents an integrated approach for modelling enterprise architectures using UML. To satisfy a need for a wide range of modelling choices, we provide a rich set of process-based and role-based modelling concepts, together with a flexible way of associating business events with business processes and roles. Our approach enriches Unified Modelling Language (UML) to support the requirements of enterprise distributed object computing (EDOC) systems and is currently being considered by the Object Management Group (OMG) for standardisation.

Understanding any IDL lesson one: DCE and CORBA

The co-existence of middleware platforms, eg. DCE and CORBA, creates a new problem of heterogeneity-the heterogeneity of middleware platforms. In this paper a partial approach to overcoming this heterogeneity is presented-the translation between different interface definition languages (IDL) and the comparison of interface specifications in different IDLs. In particular, a mapping between DCE IDL and OMG IDL and the corresponding translation tools are presented. Furthermore, various definitions of sub-typing of interface specifications are investigated for their suitability in comparing specifications in different IDLs.

Trader Down Under: Upside down and inside out

In this article we present a new object-oriented design of a trader customized to the CORBA environment as a CORBA Service. Key design decisions include the separation of trader, service types, and service offers, the reuse of OMGs CORBA services, and the application of a fine-grain object model. Emphasis is also placed on the federation of traders by specifying interfaces for this purpose and a federation protocol. The fine-grain object model allows a wide range of implementations and configurations to satisfy different user requirements. This design is an object-oriented alternative to the trader specification to be adopted by the OMG.

Mapping enterprise events to the CORBA notification service

To satisfy the need for a wide range of enterprise modelling choices, it is necessary to have a rich set of process based and role based modelling concepts. It is also necessary to have a sound and expressive business event model that includes a flexible way of associating business events with business processes and roles. However, the ability to construct detailed and expressive enterprise models is not useful in a business context without some means of realising the model in technology. The paper introduces the basic modelling concepts from the DSTCs UML Profile for Enterprise Distributed Object Computing before describing in detail the profiles business event model. The paper then describes how this event model can be mapped in a straightforward manner to implementations using the OMGs CORBA Notification Service. This mapping can then be used as the basis for building automated tools that support generating implementations of systems from high level enterprise models.

Mapping Enterprise Roles to CORBA Objects Using Trader

The ODP Enterprise Language concept of Role provides a useful abstraction for behaviour in a context that is independent of how the behaviour is enacted in a run time system. In CORBA implementations of ODP systems a client object reference variable is analogous to a Role – it is a placeholder for an object whose behaviour is specified by an IDL type. The DSTC UML Profile for Enterprise Distributed Object Computing expresses the Role concept as a UML Action, which is a placeholder for behaviour in UML, and has an attribute representing constraints on the objects that may perform the behaviour (fill the Role). CORBA Object reference variables are assigned to object references using some “bootstrapping mechanism”, implemented by a programmer, perhaps using a Trader or Naming Service to locate suitable objects. For the first time in UML, the DSTC EDOC Profile allows designers to specify Roles independent of the class of objects that may perform the Roles. Designers also specify which objects are appropriate for filling which Roles. Furthermore the mapping of this Profile to CORBA technology allows automatic generation of Trader query code to bootstrap the object references of a distributed application according to the high-level design, not the whims of the programmer.

Elemental and Pegamento: the final cut applying the MDA pattern

We provide an investigation of the applicability of the model driven architecture /spl trade/ to the development of a technical architecture in a specific domain, viz: contract monitoring. We define MDA in terms of a single basic pattern, which is then composed in several ways to represent the behaviour of a large range of MDA tools. The paper introduces both the work of the Elemental project to provide the domain example, and the Pegamento project to explain the metamodels and tools in the MDA framework which might be applied to the domain. Elemental has developed an architecture and a language for supporting enterprise contract management (ECM) as part of an extended enterprise model. Pegamento has specified and built MDA prototype tools using several modelling languages, meta-languages and platforms. As the work of both these projects reaches maturity, the Final Cut is our proposed application of this toolset to facilitate building a model-based implementation of the relevant parts of Elementals ECM system. We discover several generic MDA pattern matches in this case study, and several specific to the ECM. We also identify and discuss pattern mismatches.

ODP and OMA Reference Models

The Reference Model of Open Distributed Processing (RM-ODP) was a joint effort by the international standards bodies ISO and ITU-T to develop a generic architecture for the standardisation of open distributed processing (ODP). The model describes a framework within which support of distribution, interworking, interoperability and portability can be integrated. The Object Management Architecture (OMA) was developed by the Object Management Group (OMG) as a specific architecture based on the generic principles and structures of RM-ODP. The OMA provides a framework for an integrated suite of standards for object-oriented distributed computing.