Diversity in distributed applications leads to diversity in distribution models, and hence in middleware. However, large systems may need different types of middleware and interoperability between them, requiring ``Middleware to Middleware'' architectures. We have introduced the schizophrenic middleware concept as a general solution for interoperability between distribution models. PolyORB, our implementation of a schizophrenic middleware, demonstrates full interoperability between CORBA, SOAP, and the Ada 95 Distributed System Annex (DSA). In this paper, we present an assessment of the usability of our platform to implement Message Oriented Middleware (MOM). We then study MOM and ORB interoperability, from both an architectural and a functional point of view, and finally discuss benefits provided by our architecture to implement middleware.

Using a middleware when designing a new distributed application allows portability across numerous software and hardware architectures, but introduces a new layer of potential incompatibilities due to the existence of various middleware standards. PolyORB, our generic middleware, directly addresses this problem: interoperability between distribution models. It can be customized into several ``personalities'' (e.g. CORBA, or RMI, or Ada 95 DSA), such as Jonathan and Quarterware. It also provides simultaneous support of multiple personalities within a single middleware instance. Software component implemented using a given distribution model may thus interact with remote entities from a different distribution model. This paper identifies the functions required to implement such a middleware and maps them on an operational design.

This paper presents our work to bridge the Ada 95 Distributed Systems Annex (DSA) and CORBA to take advantages of both environments facilities. Our project consists in two successive steps. The first one is CIAO, a DSA to CORBA translator. The second one aims at the definition of a generic middleware to be customized to DSA and CORBA. We propose a definition and an architecture of services for a generic middleware DROOPI and explain how it can be customized according various criteria. This generic middleware takes advantage of the lessons learned in the design and the development of several other projects: GLADE, AdaBroker and CIAO. Therefore, in its motivation and its targetting, we believe DROOPI is an original project.

Using a middleware when designing a new distributed application allows portability across numerous software and hardware architectures, but introduces a new layer of potential incompatibilities due to the existence of various middleware standards. This paper presents the architecture of DROOPI (Distributed Reusable Object-Oriented Polymorphic Infrastructure). This project aims at defining and implementing a modular middleware emphasizing software reuse, customizability towards environment and application requirements, and transparent interoperability through the support of multiple middleware personalities. Some of these capabilities may be found in similar projects. Our objective is to bring all these properties in a single environment, enabling communication between various components using different middleware standards.

This article presents the state of the art in the implementation of distributed objet systems using the Ada 95 language. The Distributed Systems optional annex of the Ada 95 standard is first descsribed, as well as an implementation of this annex: GLADE. Usage of the CORBA platform in Ada 95 is then discussed. Present solutions and current research work on interoperation of both systems is finally presented.

Comparing CORBA and the Ada 95 Distributed Systems Annex shows that an advantage of CORBA is its Common Object Services, providing standard, frequently-used components for distributed application development. This paper presents our implementation of similar services for the DSA. We also introduce new developments of our team that aim at providing close interaction between CORBA and Ada applications. Part of the work presented here was accomplished by the AdaBroker team: Fabien Azavant, Emmanuel Chavane, Jean-Marie Cottin, Tristan Gingold, Laurent Kübler, Vincent Niebel, and Sébastien Ponce.

While the Distributed Systems Annex of Ada 95 provides developers with a framework for easy contruction of safe distributed systems, integrating distribution seamlessly in the strong typing and well-defined semantics of Ada, it lacks the cross-platform, multiple-languages capabilities offered by CORBA. This paper presents CIAO (CORBA Interface for Ada distributed Objects), a tool for automated generation of proxies that allow CORBA clients to interact with services created using the Distributed Systems Annex. A representation of DSA service specifications in OMG IDL is first presented. We then describe an automated translation tool based on this representation model. This tool is based on ASIS, a standardized API for the extraction of syntactic and semantic information from an Ada compilation environment.

This paper presents a comparison between CORBA and the Ada 95 Distributed Systems Annex. We also focus on the latest developments made by the ENST research team to GLADE that are related to CORBA services.