The Assurance Point Model for Consistency and Recovery in Service Composition

Abstract

This research has defined an abstract execution model for establishing user-defined correctness and recovery in a service composition environment. The service composition model defines a hierarchical service composition structure, where a service is composed of atomic and/or composite groups. The model provides multi-level protection against service execution failure by using compensation and contingency at different composition granularity levels. The model is enhanced with the concept of assurance points (APS) and integration rules, where APs serve as logical and physical checkpoints for user-defined consistency checking, invoking integration rules that check pre and post conditions at different points in the execution process. The unique aspect of APs is that they provide intermediate rollback points when failures occur, thus allowing a process to be compensated to a specific AP for the purpose of rechecking pre-conditions before retry attempts. APs also support a dynamic backward recovery process, known as cascaded contingency, for hierarchically nested processes in an attempt to recover to a previous AP that can be used to invoke contingent procedures or alternate execution paths for failure of a nested process. As a result, the assurance point approach provides flexibility with respect to the combined use of backward and forward recovery options. Petri Nets have been used to define the semantics of the assurance point approach to service composition and recovery. A comparison to the BPEL fault handler is also provided.