BACKWARD ERROR RECOVERY VIA CONVERSATIONS IN ADA

An approach is proposed for using backward error recovery in Ada. The advantages and disadvantages of Ada are not discussed, nor are new run -time algorithms for Ada proposed, but a practical method is offered f or using backward recovery and software diversity within this language . The authors believe that Ada has sufficient facilities to allow the use of software diversity to develop fault-tolerant systems. However, previous researchers have noticed problems in attempting to use this p ossibility, and restrictive rules are necessary to avoid these problem s. 'Conversations' for co-ordinated backward recovery of concurrent pr ocesses are considered and the following proposals are made: a restric ted scheme similar to Kim's 'concurrent recovery block', but providing for deadlines on the execution of the diverse modules; programming ru les for applying this scheme to Ada procedures; and a way for automati cally enforcing these rules through a source code pre-processor. Two a dvantages of this scheme are its functioning within this widely used c onventional industrial language and its suitability for real-time syst ems of an iterative type.