La reconciliation de copies divergentes est un probleme general qui se pose dans les systemes repartis, le travail collaboratif, l'ingenierie distribuee, le genie logiciel et les systemes de controle de versions ainsi que dans le travail individuel mettant en jeu plusieurs postes mobiles. Les synchroniseurs fournissent une reponse a ce probleme en permettant de reconcilier deux copies divergentes du meme objet. Malheureusement leur utilisation pour reconcilier n copies necessite l'existence d'un composant central (copie de reference, site particulier) sans quoi la convergence des copies n'est pas assuree. Ce papier presente les principes et l'algorithme d'un Synchroniseur qui permet d'obtenir la reconciliation de n copies, sans privilegier de copie ou de site particuliers. Les copies peuvent avoir ete modifiees (en concurrence ou non) sur les differents sites, le Synchroniseur propose permet de les reconcilier deux a deux, a n'importe quel moment, par association de couples quelconques. Son grand interet est de permettre la propagation libre et paresseuse des mises a jour effectuees sur les differentes copies tout en garantissant a terme leur convergence.

Reconciling divergent copies is a problem encountered in distributed systems, groupware, version control systems and personal work involving several mobile computing devices. Published reconciliation methods, whether synchronous or asynchronous, require some ordering facility provided either by a central component (master copy, sequencer) or by a fully distributed mechanism (timestamps, state vectors,...). Nevertheless, scalability is limited. This paper presents an asynchronous algorithm based on Operational Transformations which provides the means to reconcile any number of copies, without this limitation. Copies can be modified (concurrently or not) and then reconciled pair-wise, at any time, regardless of the pair, while their convergence is achieved. Its main advantage is thus to enable free propagation of update operations while ensuring they will be ordered in the same global order.

Reconciling divergent copies is a common problem encountered in distributed or mobile systems, asynchro-nous collaborative groupware, concurrent engineering, software configuration management, version control systems and personal work involving several mobile computing devices. Synchronizers provide a solution by enabling two divergent copies of the same object to be reconciled. Unfortunately, a master copy is gener-ally required before they can be used for reconciling n copies, otherwise copy convergence will not be achieved. This paper presents the principles and algorithm of a Synchronizer which provides the means to reconcile n copies, without discriminating in favour of any particular copy. Copies can be modified (concur-rently or not) on different sites and the Synchronizer we propose enables them to be reconciled pairwise, at any time, regardless of the pair, while achieving convergence of all copies. For this purpose, it uses the history of operations executed on each copy and Operational Transformations. It does not require a central-ised or ordering (timestamp, state vector, etc.) mechanism. Its main advantage is thus to enable free and lazy propagation of copy updates while ensuring their convergence – it is particularly suitable for P2P environ-ments in which no copy should be favoured.

In this paper, we describe the problems involved in integrating concurrency control into object-oriented database systems. The object-oriented approach places specific constraints on concurrency between transactions, which we discuss. We then propose an adaptation of the locking technique to satisfy them, without unnecessarily restricting concurrency. Finally, we analyse in detail the impacts of both the transaction model and the locking granularity imposed by the underlying system. The solutions proposed are illustrated with the O2 system developed by the Altaïr GIP.

Transactional systems are based on two distinct transaction models: the update in place model (UIP) and the deferred update model (DU). When considering typed objects relative to concurrency, the expression of commutativity depends on the transaction model on which it is applied: backward commutativity for the UIP model and forward commutativity for the DU model. These two relationships cannot be compared with regard to the concurrency allowed between transactions, as the executions generated by each model are different. This paper combines backward and forward commutativity relations in a new relationship, named Forward-Backward commutativity. This relationship includes both previous ones and provides more concurrency than the union of both. Furthermore, the paper proposes a new concurrency and recovery protocol using this relation, based on biversion objects. Biversion objects are only needed during concurrent executions.

In distributed collaborative systems, replicated objects, shared by users, are subject to concurrency constraints. All methods [4, 13, 18, 15, 16, 19, 22] proposed to serialize concurrent operations and achieve copies convergence of replicated objects are based on the use of Operational Transformations. In this context, giving the user the ability to undo an operation has been recognized as a difficult problem [1, 2, 3, 12, 14, 20, 21]. The few general propositions to solve the problem sometimes compromise copies convergence and/or users' intention, insofar as the Operational Transformations used are unsuitable for undo. This paper has a twofold objective. Firstly, it aims to highlight two general conditions (named C3 and C4) that need to be satisfied by any transformation adapted to undo. Secondly, it presents a general undo algorithm based on the definition of a generic undo-fitted transformation, which automatically verifies these conditions. The interest of the proposed method is that the undoing of an operation obeys to the same processing as the one used for regular operations in collaborative systems such as [15,19].

Cette chronique est le resultat d'un travail collectif realise par les membres de l'action specifique CNRS « Mobilite/Acces aux donnees » [AS_BDMobile]. Elle fait le point sur l'etat d'avancement des travaux realises dans le domaine des bases de donnees mobiles et identifie quelques orientations de recherche jugees particulierement pertinentes. Pour des raisons editoriales, cette chronique est publiee en deux parties d'egale importance apparaissant dans deux numeros successifs de la revue TSI. La premiere partie de la chronique presente une classification des applications mobiles et une caracterisation de leur environnement d'execution ainsi qu'une analyse des problematiques suivantes : gestion des donnees de localisation, modeles d'acces aux donnees, coherence des traitements et synchronisation de copies. Ce document constitue quant a lui la seconde partie de cette chronique et se concentre sur la gestion de donnees embarquees dans des calculateurs ultralegers, la confidentialite des donnees et enfin l'adaptabilite des infrastructures logicielles a la mobilite et a la deconnexion.

This paper reports on the main results of a specific action on mobile databases conducted by CNRS in France from October 2001 to December 2002. The objective was to review the state of progress in mobile databases and identify major research directions for the French database community. This paper gives an outline of the directions in which the action participants are now engaged, namely: copy synchronization in disconnected computing, mobile transactions, database embedded in ultra-light devices, data confidentiality, P2P dissemination models and middleware adaptability.

In real-time collaborative systems, replicated objects, shared by users, are subject to concurrency constraints. In order to satisfy these, various algorithms, qualified as op?timistic, [3, 5, 13, 17, 14, 15, 18], have been proposed that exploit the semantic properties of operations to serialize concurrent operations and achieve copy con?vergence of replicated objects. Their drawback is that they either re?quire a condition on user's operations which is hard to verify when possible to ensure, or they need undo?ing then redoing operations in some situations. The main purpose of this paper is to present two new algorithms that over?come these drawbacks. They are based upon the imple?mentation of a continuous global order which enables that condition to be released, and simplifies the operation inte?gration process. In the second algorithm, thanks to de?ferred broadcast of operations to other sites, this process becomes even more simplified.

Les applications et systemes cooperatifs, ou plusieurs utilisateurs accedent simultanement a des donnees communes, offrent des problemes particuliers vis-a-vis de la coherence des donnees qu'ils manipulent. En particulier, les approches classiques issues des systemes d'exploitation ou des systemes de bases de donnees sont prises en defaut puisque basees sur la mise en oeuvre d'acces exclusifs aux donnees (moniteurs, transactions isolees). On classe generalement les applications cooperatives en deux categories : les applications synchrones, ou les utilisateurs accedent a des objets communs au meme instant, et les applications asynchrones, ou les utilisateurs accedent aux objets partages a des moments differents. Chaque categorie voit des solutions specifiques au probleme de la coherence des donnees. Nous presentons ici deux approches, l'une tournee vers les systemes synchrones et l'autre vers les systemes asynchrones.

Article Free Access Share on Serialization of concurrent operations in a distributed collaborative environment Authors: Maher Suleiman LSI, University of Montpellier II, 860, rue de St Priest, 34090 Montpellier LSI, University of Montpellier II, 860, rue de St Priest, 34090 MontpellierView Profile , Michèle Cart LSI, University of Montpellier II, 860, rue de St Priest, 34090 Montpellier LSI, University of Montpellier II, 860, rue de St Priest, 34090 MontpellierView Profile , Jean Ferrié LSI, University of Montpellier II, 860, rue de St Priest, 34090 Montpellier LSI, University of Montpellier II, 860, rue de St Priest, 34090 MontpellierView Profile Authors Info & Claims GROUP '97: Proceedings of the international ACM SIGGROUP conference on Supporting group work: the integration challengeNovember 1997 Pages 435–445https://doi.org/10.1145/266838.267369Online:16 November 1997Publication History 59citation734DownloadsMetricsTotal Citations59Total Downloads734Last 12 Months39Last 6 weeks9 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

The emergence of new criteria specifically adapted to multidatabase systems, in response to constraints imposed by global serializability, leads to restrictive hypotheses in order to ensure correctness of executions. This is the case with the two level serializability presented in [6], that ensures strongly correct executions if transaction programs are Local Database Preserving (LDP). The main drawback of the LDP hypothesis is that it relies on rigorous programming. The principal objective of this paper has been to suppress this drawback while conserving the strong correctness of 2LSR executions We propose defining precisely the notion of value dependencies, and managing them so as not to impose the LDP property.

In this paper, we describe the problems involved in integrating concurrency control into object-oriented database systems. The object-oriented approach places specific constraints on concurrency between transactions, which we discuss. We then propose an adaptation of the locking technique to satisfy them, without unnecessarily restricting concurrency. Finally, we analyse in detail the impacts of both the transaction model and the locking granularity imposed by the underlying system. The solutions proposed are illustrated with the O2 system developed by the Altair GIP.