A Comparison of Optimistic Approaches to Collaborative Editing of Wiki Pages

Wikis, a popular tool for sharing knowledge, are basically collaborative editing systems. However, existing wiki systems offer limited support for co-operative authoring, and they do not scale well, because they are based on a centralised architecture. This paper compares the well-known centralised MediaWiki system with several peer-to-peer approaches to editing of wiki pages: an operational transformation approach (MOT2), a commutativity-oriented approach (WOOTO) and a conflict resolution approach (ACF). We evaluate and compare them, according to a number of qualitative and quantitative metrics

Système et réseaux informatiques : fonctions frontales dans un environnement reparti bati sur un réseau

L'étude des réseaux a jusqu'à maintenant été abordée par l'aspect télécommunication en repoussant à plus long terme les points de vue système et externe. L'aspect externe concerne l'utilisateur qui se voit confronté à une multitude de systèmes d'exploitation différents. Or, très peu d'utilisateurs peuvent prétendre connaitre parfaitement deux ou plusieurs systèmes; ce que l'on pensait être un avantage des réseaux généraux devient donc un inconvénient. Avec leur développement croissant et notamment l'entrée dans l'ère de la télématique, il semble que le moment soit venu de chercher à faciliter l'utilisation de l'outil informatique dans le cadre d'une informatique répartie.No abstrac

Asynchronous Reconciliation based on Operational Transformation for P2P Collaborative Environments

International audienceReconciling 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

Synchronizer Based on Operational Transformation for P2P Environments

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

Concurrent Undo Operations in Collaborative Environments using Operational Transformation

International audienceIn 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]

A Cooperative Approach to View Selection and Placement in P2P Systems

International audienceP2P systems are becoming increasingly popular as they enable users to exchange digital information by participating in complex networks. However, limited work has been done on employing materialized views in P2P data ware-housing systems. We argue that this technique can be applied in P2P data sharing for (i) saving work for frequently asked queries and (ii) increasing availability in cases of failures. In this paper, we present an approach for dynamically selecting an effective set of views to be materialized and place them in key points in the P2P system so as to achieve the best combination of good query performance and low view maintenance cost, given a limited amount of storage space at each peer. Moreover, as the system is dynamic, our approach continuously monitors the incoming query and adjusts the system configuration by removing materialized views in order to replace the less beneficial views with more beneficial ones

View Selection and Placement in Distributed Data Warehousing Systems

International audienc

Copies convergence in a distributed real-time collaborative environment

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

Leveraging Social and Content-based Recommendation in P2P Systems

International audienceWe focus on peer-to-peer (P2P) content recommendation for on-line communities, where social relationships between users can be exploited as a parameter to increase the trust of recommendation. Most of the existing solutions establish friendship relationships based on users behavior or declared trust. In this paper, we propose a novel P2P recommendation approach (called F2Frec) that leverages content and social-based recommendation by maintaining a P2P and friend-to-friend network. This network is used as a basis to provide useful and high quality recommendations. Based on F2Frec, we propose new metrics, such as usefulness and similarity (among users and their respective friend network), necessary to enable friendship establishment and to select recommendations. We define our proposed metrics based on users' topic of interest and relevant topics that are automatically extracted from the contents stored by each user. Our experimental evaluation, using the TREC09 dataset and Wiki vote social network, shows the benefits of our approach compared to anonymous recommendation. In addition, we show that F2Frec increases recall by a factor of 8.8 compared with centralized collaborative filtering