Format specification of CORBA services: Experience and lessons learned.

CORBA is now established as one of the main contenders in object-oriented m iddleware. Beyond the definition of this standard for distributed object sy stems, the Object Management Group (OMG) has specified several object servi ces (Common Object Services, COS) that should foster the interoperability o f 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 substi tutable 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 an d 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 under-specifications. We show that the choices made by the implementers lead to incompatible impleme ntations. We finally suggest a solution to overcome the problem of specific ation of object services, which satisfies the views of both implementers an d users. Specifically, we suggest that the specification of such services b e made using a formal description technique, and that implementers be provi ded with test cases derived from the formal specification.