Spécification et analyse d’un protocole de contrôle d’accès optimiste pour éditeurs collaboratifs répartis

Abstract

Distributed Collaborative Editors are interactive systems where several and dispersed users edit concurrently shared documents. Generally, these systems rely on data replication and use safe synchronization protocol which ensures data consistency even though the users’s updates are executed in any order on different copies. Controlling access in such systems is a challenging problem, as they need dynamic access changes and low latency access to shared documents. In (Imine et al., 2009), a flexible access control protocol is proposed; it is based on replicating the shared document and its authorization policy at the local memory of each user. To deal with latency and dynamic access changes, an optimisticaccess control technique is used where enforcement of authorizations is retroactive. However, verifying whether the combination of access control and synchronization protocol preserves the data consistency is a hard task since it requires examining a large number of situations.In this paper, we show how to specify and verify formally an access control protocol designed for Distributed Collaborative Editor. The analysis let to conclude that the protocol preserves consistency in such a way that the access control policy is enforced identically at all participating user sites. Most importantly, this analysis enables us to validate some conceptual choices of the protocol.