An exception handling framework for N-version programming in object-oriented systems

An approach to introducing exception handling into object oriented N-version programming (NVP) is proposed. General principles of structuring systems with diversity are outlined. The importance of using exceptions while applying diversely developed software is shown. Internal and external exceptions are clearly separated in our framework: each version has its own internal exceptions but the external exceptions of all versions have to be the same and identical to the interface exceptions of the diversely designed class. This scheme requires an adjudicator of a special kind to allow signalling interface exceptions when a majority of versions have signalled the same exception. These ideas are demonstrated using a general class diversity framework developed recently. An Ada implementation is outlined.