CORBA is now established as one of the main contenders in object-oriented middleware.Beyond the definition of this standard for distributed object systems, the Object Management Group (OMG) has specified several object services (Common Object Services, COS) that should foster the interoperability of distributed applications.Based on experiment, the goal of this paper is to show that the OMG's style of specification of the CORBA services is not suited to guarantee that implementers will produce interoperable and substitutable implementations.To illustrate our point, we give an account of an experiment based upon the formal specification of one COS, namely the CORBA Event Service.This formal specification highlights several ambiguities and under-specifications in the OMG document.We then test several commercial and public domain implementations of the CORBA Event Service, in order to assess how the implementers have dealt with these underspecifications.We show that the choices made by the implementers lead to incompatible implementations.We finally suggest a solution to overcome the problem of specification of object services, which satisfies the views of both implementers and users.Specifically, we suggest that the specification of such services be made using a formal description technique, and that implementers be provided with test cases derived from the formal specification.

CORBA is a standard proposed by the Object Management Group (OMG) in order to promote interoperability between distributed object systems. CORBA provides a programming-language neutral Interface Definition Language (IDL) that describes the syntactic aspects of services supported by remote objects. However, CORBA IDL does not provide any means to specify the behavior of objects in an abstract and formal way. In the current practice, behavioral specification is provided either in plain English, or directly in the programming language chosen for the implementation. We propose to extend the CORBA interface definition of distributed objects by a behavioral specification based on high level Petri nets. We detail at the syntactic and semantic level how this formalism supports the features of the CORBA object model. We present a realistic case study to demonstrate our approach. Our technique allows specifying in an abstract, concise and precise way the behavior of CORBA servers, including internal concurrency and synchronization. As the behavioral specification is fully executable, this approach also enables to prototype and test a distributed object system as soon as the behaviors of individual objects have been defined. The paper discusses several implementation issues of the tool that supports the edition of models and their interactive excution. The high level of formality of the chosen formalism allows for mathematical analysis of behavioral specifications. Copyright © 2000 John Wiley & Sons, Ltd.