The chief aim of this survey is to discuss exception handling models which have been developed for concurrent object systems. In conducting this discussion we rely on the following fundamental principles: exception handling should be associated with structuring techniques; concurrent systems require exception handling which is different from that used in sequential systems; concurrent systems are best structured out of (nested) actions; atomicity of actions is crucial for developing complex systems. In this survey we adhere to the wellknown classification of concurrent systems, developed in the 70s by C.A.R. Hoare, J.J. Horning and B. Randell, into cooperative, competitive and disjoint ones. Competitive systems are structured using atomic transactions. Atomic actions are used for structuring cooperative systems. Complex systems in which components can compete and cooperate are structured using Coordinated Atomic actions. The focus of the survey is on outlining models and schemes which combine these action-based structuring approaches with exception handling. In conclusion we emphasise that exception handling models should be adequate to the system development paradigm and structuring approaches used.

Although the number of proposals discussing various atomic action schemes is increasing, these schemes are very rarely used in designing practical applications. To a large extent, this is accounted for by the gap existing between the languages used in research and the standard or widely spread languages (e.g. C, C++, Ada 83, Ada 95, Java) employed by practitioners. Moreover, very often researchers extend languages with new features or invent new languages to express their ideas better. Even though these approaches seem to be quite natural, they widen the gap between practice and research. To bridge this gap, we should consider fault tolerance schemes in terms of a standard language, taking the language itself for granted. The question which we believe should be addressed is how to use/implement a particular scheme in these languages rather than how to modify the language. Only in this way the schemes could be used directly and the application domains of atomic action schemes extended. The main intention of this paper is to summarise research that has been done in the last years in designing various atomic action and