Section: New Results

Collaborative Data Management

A Framework to Design Conflict-Free Replicated Data Types

Participants : Mehdi Ahmed-Nacer, Stéphane Martin, Pascal Urso.

Design new eventually consistent data types is difficult and error-prone as demonstrated by the numerous proposed approaches that fail to resolve conflicts for simple plain text document. Moreover, more the data type is complex, more conflicts types must be resolved. We have presented a layered approach to design new eventually consistent data types [21] , [15] . This approach decouples eventual consistency management from data type constraints satisfaction. We compose one or several existing replicated data types which ensure eventual consistency, and adaptation layers to obtain a new eventually consistent data type. Each layer or replicated data type can be freely substituted by one providing the same interface. We have demonstrated that our approach is implementable and obtains acceptable performances. Our experiments and implementation are publicly available and re-playable (https://github.com/score-team/replication-benchmarker ).

Enhancing Rich Content Wikis with Real-Time Collaboration

Participants : Luc André, Claudia-Lavinia Ignat, Gérald Oster.

Wikis are one of the most important tools of Web 2.0 allowing users to easily edit shared data. WYSIWYG editors for wiki pages avoid the impediments of learning wiki syntax. However, wikis offer poor support for merging concurrent contributions on the same pages. Users have to manually merge concurrent changes and there is no support for an automatic merging. As real-time collaborative editing reduces the number of conflicts as the time frame for concurrent work is very short, we proposed extending wiki systems with real-time collaboration [23] . We propose an automatic merging solution adapted for rich content wikis. Our solution is integrated as an extension of XWiki system (http://extensions.xwiki.org/xwiki/bin/view/Extension/RealTime+Wiki+Editor ).

Rapid and Round-free Multi-pair Asynchronous Push-Pull Aggregation

Participants : Claudia-Lavinia Ignat, Hyun-Gul Roh.

In the context of STREAMS project we investigated gossip-based dissemination mechanisms in peer-to-peer real-time collaboration adapted for consistency maintenance algorithms based on CRDT (Commutative Replicated Data Types). These dissemination mechanisms need to compute the size of the network and therefore a suitable rapid protocol that aggregates data over network is essential. Iterative aggregation protocols, especially push-pull style aggregations, generally need prior configurations to synchronize rounds over all nodes, and messages should be exchanged in a synchronous/blocking way in order to ensure accurate estimates in push-pull or push-sum protocols. We proposed a multi-pair asynchronous push-pull aggregation (MAPPA) [22] , which frees the push-pull aggregations from the synchronization constraints, and therefore accelerates the aggregation speed. MAPPA is resilient to network churns, and thus suitable for dynamic peer-to-peer networks.

Trustworthy contract based collaboration

Participants : Claudia-Lavinia Ignat, Hien Thi Thu Truong.

Availability of trustworthy environments is one of the main conditions that would lead to a greater acceptance and reliance on collaborative systems. In the context of large scale multi-synchronous collaboration where users work in parallel on different streams of activities a ”hard” security that would forbid many actions is unusable. We adopt instead a “soft” security where rather than adopting an a priori strict enforcement of security rules, access is given first to data without control but with restrictions that are verified a posteriori. We proposed a contract-based collaboration model [2] , [4] where we establish and adjust trust in users based on detective enforcement of basic usage control requirements. Usage control requirements are specified as contracts. Contracts are specified by data owners when they share data in accordance with user trust levels. Observation of adherence to or violation of contracts is used to adjust trust levels. Our contract-based collaboration model allows the specification of contracts, merging of data and contracts and resolution of conflicting contracts. A trust metric for computing user trust levels was proposed based on auditing user compliance to the given contracts.

Multi-synchronous collaboration maintains multiple, simultaneous streams of activity which continually diverge and converge. These streams of activity are represented by means of logs of operations, i.e. user modifications. A malicious user might tamper his log of operations. At the moment of synchronization with other streams, the tampered log might generate wrong results. A trustworthy collaboration environment should detect if logs were tampered. We proposed a mechanism for establishment of trusted logs relying on hash-chain based authenticators [17] , [18] , [2] . Our solution ensures the authenticity, the integrity of logs, and the user accountability. We proposed algorithms to construct authenticators and verify logs. We proved their correctness and provided theoretical and practical evaluations.

Distributed activity management in crisis situation

Participants : François Charoy, Joern Franke.

Crisis management has been a very fruitful domain to investigate new approaches for high value, human driven activity coordination in a multi organisational setting. Our work benefits from a large amount of use cases and detailed accounts of previous dramatic events to analyse requirements and confront our proposals. This paper present the final part of this work on the problem of replication of activities between several workspaces [3] . We are now looking for new vehicles to continue this research at an international level.