Rigorous Design of Fault-Tolerant Transactions for Replicated Database Systems Using Event B

Abstract

Abstract. System availability is improved by the replication of data objects in a distributed database system. However, during updates, the complexity of keeping replicas identical arises due to failures of sites and race conditions among conflicting transactions. Fault tolerance and reliability are key issues to be addressed in the design and architecture of these systems. Event B is a formal technique which provides a framework for developing mathematical models of distributed systems by rigorous description of the problem, gradually introducing solutions in refinement steps, and verification of solutions by discharge of proof obligations. In this paper, we present a formal development of a distributed system using Event B that ensures atomic commitment of distributed transactions consisting of communicating transaction components at participating sites. This formal approach carries the development of the system from an initial abstract specification of transactional updates on a one copy database to a detailed design containing replicated databases in refinement. Through refinement we verify that the design of the replicated database confirms to the one copy database abstraction.

Verification of Liveness Properties in Distributed Systems

“…A formal refinement based approach using Event-B to model and analyze distributed transaction is given in [11]. In our abstract model, an update transaction modifies the abstract one copy database through a single atomic event.…”

“…In this paper we outline issues related to liveness in Event-B models and present the guidelines to address these issues in the Event-B development of the distributed systems. A case study of distributed transactions [11] for replicated database is used to outline construction of proof obligations.…”

Recording Process Documentation in the Presence of Failures

“…Applying formal methods to the design and reasoning of fault-tolerance has been studied in distributed systems, e.g., distributed database systems [25], control systems [18], and mobile agent systems [19]. The ASM notation we adopt has been used previously to describe a fault-tolerant directory service for mobile agents [21] and PReP.…”

Decomposition Structures for Event-B

“…Event-B [2] provides a more flexible approach to refinement than found in Classical B [1] and in related languages such as Z [11] and VDM [10]. One important feature is the ability to introduce new events in a refinement step.…”