Flexible schemes for application-level fault tolerance

It is pointed out that the design of fault-tolerance provisions in the application level is normally necessary, but difficult and error-prone due to its ad-hoc nature. Structuring schemes have been proposed to reduce the difficulty of this task, but they appear too restrictive for the building of large, heterogeneous applications. The redundant structures that can be used in the individual components of a system depend on their requirements or inherent characteristics: it would be useful to combine components using different basic schemes. As an example, the authors propose a solution for interfacing components using conversations for backward recovery with components using atomic transactions. Constraints for the designers of the components to be interfaced and requirements on the virtual machine supporting their execution are defined. Ways a classification of components could be organized to allow the formulation of more general solutions are discussed.