Exception Handling Framework for N-Version Programming in Object Oriented Systems

摘要

Structuring complex systems out of components with both normal and exceptionaloutcomes and using exception handling for dealing with abnormal events are well-accepted practices. This paper proposes an approach for introducing exception handling into object-oriented N-version programming (NVP). We start with outlining general principles of structuring systems with diversity and show why it is important to use exceptions while developing and using diversely developed software. Internal version exceptions and external exceptions, which the diversely-designed class can propagate, are clearly separated in our framework: each of 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 whole class. This scheme requires an adjudicator of a special kind to allow interface exception signaling when a majority of versions have signaled the same exception. We demonstrate these ideas using a general framework for introducing NVP into object-oriented systems, which we have developed recently. This framework follows all principles of structured NVP: software diversity is introduced here at the level of classes and encapsulated into the diversely designed class. This framework makes use of the many advantages object oriented programming has. For the demonstration, it has been implemented in Ada.