Experiments in Model-Checking Optimistic Replication Algorithms

Hanifa Boucheneb (1) , Abdessamad Imine (2)

1 VeriForm - Laboratoire VeriForm - Department of Computer Engineering
2 CASSIS - Combination of approaches to the security of infinite states systems

This paper describes a series of model-checking experiments to verify optimistic replication algorithms based on Operational Transformation (OT) approach used for supporting collaborative edition. We formally define, using tool UPPAAL, the behavior and the main consistency requirement (i.e. convergence property) of the collaborative editing systems, as well as the abstract behavior of the environment where these systems are supposed to operate. Due to data replication and the unpredictable nature of user interactions, such systems have infinitely many states. So, we show how to exploit some features of the UPPAAL specification language to attenuate the severe state explosion problem. Two models are proposed. The first one, called concrete model, is very close to the system implementation but runs up against a severe explosion of states. The second model, called symbolic model, aims to overcome the limitation of the concrete model by delaying the effective selection and execution of editing operations until the construction of symbolic execution traces of all sites is completed. Experimental results have shown that the symbolic model allows a significant gain in both space and time. Using the symbolic model, we have been able to show that if the number of sites exceeds $2$ then the convergence property is not satisfied for all OT algorithms considered here. A counterexample is provided for every algorithm.

Mots clés: Operational transformation algorithms; Copies convergence; Model-checking; on-the-fly approach

Domaines: Logique en informatique [cs.LO]; Calcul formel [cs.SC]; Calcul parallèle, distribué et partagé [cs.DC]

Hanifa Boucheneb, Abdessamad Imine. Experiments in Model-Checking Optimistic Replication Algorithms. [Research Report] RR-6510, INRIA. 2008, pp.49. ⟨inria-00274423v2⟩