3.1 Introduction

Our scientific foundations are grounded on distributed collaborative systems supported by sophisticated data sharing mechanisms and on service oriented computing with an emphasis on orchestration and on non-functional properties. Distributed collaborative systems enable distributed group work supported by computer technologies. Designing such systems requires an expertise in Distributed Systems and in Computer-Supported Collaborative Work. Besides theoretical and technical aspects of distributed systems, the design of distributed collaborative systems must take into account the human factor to offer solutions suitable for users and groups.

The COAST team vision is to move away from a centralized authority based collaboration toward a decentralized collaboration. Users will have full control over their data. They can store them locally and decide with whom to share them. The COAST team investigates the issues related to the management of distributed shared data and coordination between users and groups.

Service-oriented Computing 23 is an established domain on which the ECOO, Score and now the COAST teams have been contributing for a long time. It refers to the general discipline that studies the development of computer applications on the web. A service is an independent software program with a specific functional context and capabilities published as a service contract (or more traditionally an API). A service composition aggregates a set of services and coordinates their interactions. The scale, the autonomy of services, the heterogeneity and some design principles underlying Service-oriented Computing open new research questions that are at the basis of our research. They span the disciplines of Distributed Computing, Software Engineering and Computer- Supported Collaborative Work (CSCW). Our approach to contribute to the general vision of Service-oriented Computing is to focus on the issue of the efficient and flexible construction of reliable and secure high-level services. We aim to achieve it through the coordination/orchestration/composition of other services provided by distributed organizations or people.

3.2 Consistency Models for Distributed Collaborative Systems

Collaborative systems are distributed systems that allow users to share data. One important issue is to manage the consistency of shared data according to concurrent access. Traditional consistency criteria such as serializability, linearizability are not adequate for collaborative systems. Causality, Convergence and Intention preservation (CCI)  26 are more suitable for developing middleware for collaborative applications. We develop algorithms for ensuring CCI properties on collaborative distributed systems. Constraints on the algorithms are different according to the kind of distributed system and to the data structure. The distributed system can be centralized, decentralized or peer-to-peer. The type of data can include strings, growable arrays, ordered trees, semantic graphs and multimedia data.

3.3 Optimistic Replication

Replication of data among different nodes of a network promotes reliability, fault tolerance, and availability. When data are mutable, consistency among the different replicas must be ensured. Pessimistic replication is based on the principle of single-copy consistency while optimistic replication allows the replicas to diverge during a short time period. The consistency model for optimistic replication  25 is called eventual consistency, meaning that replicas are guaranteed to converge to the same value when the system is idle. Our research focuses on the two most promising families of optimistic replication algorithms for ensuring CCI:

• operational transformation (OT) algorithms  21
• algorithms based on conflict-free replicated data types (CRDT)  24.

Operational transformation algorithms are based on the application of a transformation function when a remote modification is integrated into the local document. Integration algorithms are generic, being parametrised by operational transformation functions which depend on replicated document types. The advantage of these algorithms is their genericity. These algorithms can be applied to any data type and they can merge heterogeneous data in a uniform manner. Commutative replicated data types are a new class of algorithms initiated by WooT 22, the first algorithm designed WithOut Operational Transformations. They ensure consistency of highly dynamic content on peer-to-peer networks. Unlike traditional optimistic replication algorithms, they can ensure consistency without concurrency control. CRDT algorithms rely on natively commutative operations defined on abstract data types such as lists or ordered trees. Thus, they do not require a merge algorithm or an integration procedure.

3.4 Process Orchestration and Management

Process Orchestration and Management is considered as a core discipline behind Service Management and Computing. It includes the analysis, the modelling, the execution, the monitoring and the continuous improvement of enterprise processes and is for us a central domain of study. Many efforts have been devoted to establishing standard business process models founded on well-grounded theories (e.g. Petri Nets) that meet the needs of business analysts, software engineers and software integrators. This has led to heated debate in the Business Process Management (BPM) community as the two points of view are very difficult to reconcile. On one side, business people in general require models that are easy to use and understand and that can be quickly adapted to exceptional situations. On the other side, IT people need models with an operational semantics in order to be able to transform them into executable artifacts. Part of our work has been an attempt to reconcile these points of view. This resulted in the development of the Bonita BPM system. It also resulted more recently in our work on crisis management where the same people are designing, executing and monitoring the process as it executes. More generally, and at a larger scale, we have been considering the problem of processes spanning the barriers of organizations. This leads to the more general problem of service composition as a way to coordinate inter organizational construction of applications. These applications provide value, based on the composition of lower level services  19.

4.1 Crisis Management

Crisis management research investigates all the dimensions regarding the management of unexpected catastrophic events like floods, earthquakes, terrorist attacks or pandemics. All the phases of a crisis, from preparedness to recovery require collaboration between people from many organizations. This provides opportunities to study inter-organizational collaboration at a large scale and to propose and evaluate mechanisms that ensure secure and safe collaboration. The PhD thesis of Béatrice Linot supervised by François Charoy and Jérôme Dinet and defended in 2021 provided us with a deep understanding of the factors that encourage collaboration and help to maintain trustworthy collaboration between stakeholders. This work is continued by the PhD thesis of Clélie Amiot who studies the effects of human chat-bot collaboration in this kind of setting 8 and with the PhD thesis of Lisa Formentini who studies the impact of the Covid lockdown on firefighters work practices and ecology of artefacts 12.

4.2 Collaborative Editing

Collaborative editing is a common application of optimistic replication in distributed settings. The goal of collaborative editors, irrespective of the kind of document, is to allow a group of users to update a document concurrently while ensuring that they eventually get all the same copy at the end. Our algorithm allows us to implement a collaborative editor in a peer-to-peer way. It avoids the need for a central server ensuring a higher level of privacy among collaborators. The domain of collaborative editing requires us to consider the problem of access control of participants and group key management 9.

4.3 Peer-to-peer storage

Peer-to-peer storage systems use the combined capacity of the peers to provide storage functionality to end users. Peer-to-peer storage systems are designed to provide persistence and availability of the stored content despite unreliability of the individual autonomous peers in a decentralised environment. We started to apply our work on data replication 18, Erasure Coding (EC) 17 and group key management 9 for IPFS (InterPlanetary File System) peer-to-peer storage and we will transfer it to Hivenet.

5.1 Footprint of research activities

In terms of practices, since the Covid-19 pandemic, the number of flights for team members has significantly decreased. Remote participation is prioritized when appropriate, and train travel is favored whenever feasible. Additionally, we prioritize conferences within Europe and have shifted away from systematically accompanying PhD students presenting their work. Regarding hardware purchases, each team member uses a low-power consumption laptop as their primary device, which remains in use for at least the duration of its warranty (five years) and often beyond.

5.2 Impact of research results

Our research on large-scale distributed collaborative systems focuses on enabling remote work, thereby supporting the reduction of office space requirements. It also examines the social dimensions of remote collaboration and home-office setups, which can contribute to decreased energy consumption. These potential benefits are emphasized in the Intergovernmental Panel on Climate Change (IPCC)’s Sixth Assessment Report – Working Group III: Mitigation of Climate Change. Our work on distributed collaborative systems can be used to exploit the underused computer resources and thus reduce the energy overhead of datacenters, such as cooling whose costs represent about 40% of the total energy consumption of a datacenter.

7.1 New software

8.1 CRDTs for Replicated Relational Databases with Integrity Constraints

Participants: Victorien Elvinger, Ba Habibatou, Claudia-Lavinia Ignat.

Many offline-first applications use an embedded relational database, such as SQLite, to manage their data. The replication of the database eases the addition of collaborative features to its applications. Most of the approaches for replicating a relational database require coordination at some extent. A few approaches propose a coordination-less replication to allow offline work. These approaches are limited in two ways: (i) They do not respect Strong Eventual Consistency that states that two replicas converge as soon as they integrate the same set of modifications; (ii) They fail to preserve the combined effect of operations’ intent in complex scenarios.

In 11 we proposed a new CRDT for replicating relations and maintaining integrity constraints in face of concurrent modifications. In contrast to previous approaches, our proposal enforces Strong Eventual Consistency and respects combined effect of operations’ intent in complex scenarios. Its replicated state consists of the composition of CRDT primitives. The state of the database is computed from the replicated state by deterministically resolving all integrity violations. Local modifications are compensated in a way that ensures the preservation of combined effect of operations’ intent.

8.2 Distributed Delivery Service for Group Key Agreement Protocols

Participants: Davide Frey [WIDE team], Claudia-Lavinia Ignat, Ludovic Paillat [Hivenet], Mathieu Turuani [PESTO team].

End-to-end encrypted messaging applications such as Signal and Whatsapp became widely popular thanks to their capability to ensure the confidentiality and integrity of online communication. While the highest security guarantees were long reserved to two-party communication, solutions for n-party communication remained either inefficient or less secure until the standardization of the MLS Protocol (Messaging Layer Security). The MLS protocol relies on a Group Key Agreement Protocol that allows members of a group to derive a common secret called group key which serves as a basis to secure group communications. It is scalable in terms of the number of operations modifying the group such as adding/removing members and it supports periodic group-key renewals preventing compromised communication. The MLS Protocol offers an efficient solution to guarantee the confidentiality and integrity of communication. However, the availability of the protocol depends on the centralized Delivery-Service component. The centralization of this component makes it an ideal target for attackers who wish to disrupt communication. Notably, with the help of a compromised Delivery Service, an attacker can prevent group members from refreshing their keys and resolving the compromise.

In order to overcome these limitations we proposed DiSCreet (Distributed delIvery Service with Context-awaRE coopEraTion), a fully distributed Delivery Service 9. It combines two distributed communication mechanisms adapted to the need of the messages exchanged by the protocol. We used a Probabilistic Reliable Broadcast mechanism to reliably deliver messages allowing users to propose changes to the group (i.e. Proposal messages) and a Cascade Consensus Protocol to deliver the messages that actually modify the group (i.e. Commit messages) and thus require an agreement between members. Our solution strengthens the availability of the MLS Protocol without compromising its security. We showed that our approach is relevant in the context of dynamic groups by conducting a theoretical study comparing DiSCreet with DCGKA, another distributed group key agreement protocol. We implementated DiSCreet based on an open source implementation of MLS.

8.3 Attacks and Defenses on the DHT of the InterPlanetary File System

Participants: Thibault Cholez [Resist team], Victor de Moura Netto, Claudia-Lavinia Ignat.

The InterPlanetary File System (IPFS), the largest decentralized peer-to-peer file system, is experiencing growing adoption with an increasing number of contributors and users. IPFS relies on Kademlia Distributed Hash Table (DHT) for publishing and fetching content. We showed that IPFS did not implement any protection mechanism proposed for Kademlia against the Sybil attacks that deny access to a given content on the network.

We evaluated the time needed to pre-compute Sybils’ cryptographic identities to target any content on IPFS. We also described and evaluated the success ratio of a localized Sybil attack denying content access on IPFS. Our experimental results 10 demonstrate unequivocally that deploying just 20 Sybils from a single IP address effectively denies content access in IPFS, revealing a critical vulnerability in its lookup process. We proposed simple yet efficient defenses that should be implemented by IPFS developers from what was proposed in the scientific literature and what was successfully implemented in similar Kademlia-based DHTs.

8.4 Distributed Access Control using CRDTs

Participants: Claudia-Lavinia Ignat, Olivier Perrin, Pierre-Antoine Rault.

Collaborative editing applications are a popular family of distributed systems that enable simultaneous document editing with other users. Their use peaked during the lockdown periods of the Covid pandemic. This highlighted their utility but also their limitations when managing large-scale collaboration. In this context, centralized systems are not suitable for several reasons. Centralized servers are vulnerable to server failures and the need for scaling. Users may then be affected by the unavailability of the applications. Nevertheless, centralized systems offer significant advantages, such as easier maintenance of consistency for shared resources. Another important aspect concerns the governance of security policies to manage different types of users and their access or modification rights for documents. In a centralized system, the single point of access simplifies this task but raises issues of censorship (a single administrator), data sovereignty (who has access to the server), and confidentiality (who has access to the data). To improve scalability, fault and attack tolerance, service transparency, and even user privacy, systems are increasingly turning to distributed architectures. In these systems, both data and security policies are replicated. Certain document modifications may conflict with changes to the policies. Conflicts are thus likely to occur, as in any distributed system—particularly given the dynamic nature of policy modifications. Conflict-free Replicated Data Types (CRDTs) are mechanisms that provide rules for resolving such conflicts.

In the context of the PhD thesis of Pierre-Antoine Rault defended on December 2024, we proposed a replication mechanism for access control that manages collaborative documents with multiple dynamic administrators. In addition to maintaining the consistency of the replicated document state and access rights, the proposed mechanism preserves the integrity of the document and prevents unauthorized modifications. We designed a CRDT to maintain consistency of data and policies in the presence of multiple administrators, without a central server. We proposed a CRDT for an access control policy based on independent rights. The use of independent rights ensures the absence of interaction between policy changes for two different rights. Our CRDT model guarantees that simultaneous policy modifications are reconciled and that replicas eventually converge. Our mechanism also ensures the correction of the document state retrospectively by compensating for the effects of unauthorized modifications that have already been applied. Our solution adds metadata to operations related to both documents and policies, allowing the evaluation of the list of document modifications that need to be reverted or applied. We proposed a validator that catalogs possible scenarios and the results of the developed algorithms.

8.5 Impact of Chatbots on Virtual Teamwork Dynamics and Performance

Participants: Clélie Amiot, François Charoy.

We studied the role of chatbots as a pivotal element in enhancing virtual teamwork. We delved into the effects of chatbots on group dynamics and performance within an online collaborative setting. To this end, a unique collaborative online activity was developed, completed with an integrated platform and a custom-designed chatbot assistant. The study involved 72 participants, systematically arranged into teams of four. These teams were further allocated into four distinct experimental conditions based on the nature of chatbot assistance provided: no assistance, private chat assistance, group chat assistance, or a combination of both.

The core findings of this investigation revealed a pronounced enhancement in team performance metrics attributable to the chatbot intervention. Teams with chatbot assistance exhibited not only improved performance but also experienced a notable reduction in response times for information requests during the collaborative activity. This improvement underscores the efficacy of chatbots in streamlining communication and information dissemination within team settings.

A particularly compelling aspect of our findings was the significant correlation observed between the chatbot’s communication capabilities and the cognitive workload of team members. Teams interacting with chatbots demonstrating higher communication proficiency reported reduced cognitive strain, suggesting that the quality of chatbot interaction plays a crucial role in the overall team experience 8.

8.6 The dynamic of ecology of artefacts for cooperation since the Covid Crisis - the case of civil security

Participants: François Charoy, Lisa Formentini.

This work explores how the artifact ecologies of civil security organizations, specifically tools and practices, evolved during and after the Covid-19 pandemic. It focuses on the shift from traditional practices to ones adapted for hybrid and remote configurations, particularly in the context of organizations like firefighters and other emergency services. It aims at understanding what remains from these new practices four years after the end and the event and what lead to this new stage in the evolution of practices. The research uses the SDIS 57 (firefighters of Moselle) as a case study to document these transformations through qualitative methods, including interviews and observational studies. While the focus is on civil security, the research aspires to benefit other long-term cooperative organizations and improve the design of collaborative tools 12.

8.7 Quantifying the Performance of Erasure Codes in P2P Storage Systems

Participants: Shadi Ibrahim [Magellan team], Thomas Lambert, Mohammad Rizk.

Traditionally, in distributed systems, the main solution to provide both availability and robustness for stored data is replication. However, one of the consequences of such a solution is the storage overhead it incurs, which is becoming increasingly problematic as the amount of stored data continues to grow each year. An alternative to replication is Erasure Coding (EC), which can provide comparable or even better robustness and availability with significantly lower storage overhead. The trade-off is that it requires additional computation for encoding and, in some cases, decoding the data.

In 17, we presented preliminary results evaluating EC within IPFS (InterPlanetary File System), a widely used peer-to-peer storage system. While the implementation is still ongoing, initial findings indicate that a naive implementation of EC in this context results in lower throughput compared to replication when adding files.

9.1 Bilateral contracts with industry

10.1 International research visitors

10.2 European initiatives

10.3 National initiatives

11.1 Promoting scientific activities

11.2 Teaching - Supervision - Juries

11.3 Popularization

12.1 Major publications

• 1 articleC.Clélie Amiot, F.François Charoy and J.Jérôme Dinet. Chatbots in Collaborative Settings and their Impact on Virtual Teamwork.Proceedings of the ACM on Human-Computer Interaction 2024. In press. HAL
• 2 articleC.-L.Claudia-Lavinia Ignat, L.Luc André and G.Gérald Oster. Enhancing rich content wikis with real-time collaboration.Concurrency and Computation: Practice and Experience338April 2021HALDOI
• 3 articleC.-L.Claudia-Lavinia Ignat, Q.-V.Quang-Vinh Dang and V.Valerie Shalin. The Influence of Trust Score on Cooperative Behavior.ACM Transactions on Internet Technology194September 2019, 1-22HALDOI
• 4 articleQ.Quentin Laporte-Chabasse, R. S.Radu S. Stoica, M.Marianne Clausel, F.François Charoy and G.Gérald Oster. Morpho-statistical description of networks through graph modelling and Bayesian inference.IEEE Transactions on Network Science and Engineering942022, 2123 - 2138HALDOI
• 5 articleH.Hoai Le Nguyen and C.-L.Claudia-Lavinia Ignat. An Analysis of Merge Conflicts and Resolutions in Git-based Open Source Projects.Computer Supported Cooperative Work273-6June 2018, 741-765HALDOI
• 6 articleM.Matthieu Nicolas, G.Gerald Oster and O.Olivier Perrin. Efficient Renaming in Sequence CRDTs.IEEE Transactions on Parallel and Distributed Systems3312December 2022, 3870-3885HALDOI
• 7 articleL.Ludovic Paillat, C.-L.Claudia-Lavinia Ignat, D.Davide Frey, M.Mathieu Turuani and A.Amine Ismail. Discreet: distributed delivery service with context-aware cooperation.Annals of Telecommunications - annales des télécommunicationsJuly 2024, 1-23HALDOI

12.2 Publications of the year

12.3 Cited publications

• 18 inproceedingsQ.Quentin Acher, C.-L.Claudia-Lavinia Ignat and S.Shadi Ibrahim. Quantifying the Performance of Conflict-free Replicated Data Types in InterPlanetary File System.Middleware 2023 Companion ProceedingsBologna, ItalyDecember 2023, 1-6HALDOIback to text
• 19 articleS.Sami Bhiri, O.Olivier Perrin, W.Walid Gaaloul and C.Claude Godart. An Object-Oriented Metamodel For Inter-Enterprises Cooperative Processes Based on Web Services.Journal of Integrated Design and Process Science82004, 37--55HALback to text
• 20 incollectionF.Fabio Casati. Promises and Failures of Research in Dynamic Service Composition.Seminal Contributions to Information Systems EngineeringSpringer Berlin Heidelberg2013, 235-239URL: http://dx.doi.org/10.1007/978-3-642-36926-1_18back to text
• 21 inproceedingsC. A.Clarence A. Ellis and S. J.Simon J. Gibbs. Concurrency Control in Groupware Systems.Proceedings of the ACM SIGMOD Conference on the Management of Data - SIGMOD 89Portland, Oregon, USAMay 1989, 399--407URL: http://doi.acm.org/10.1145/67544.66963back to textback to text
• 22 inproceedingsG.Gérald Oster, P.Pascal Urso, P.Pascal Molli and A.Abdessamad Imine. Data Consistency for P2P Collaborative Editing.ACM Conference on Computer-Supported Cooperative Work - CSCW 2006Banff, Alberta, CanadaACM Press11 2006, 259 - 268URL: http://hal.inria.fr/inria-00108523/en/back to text
• 23 articleM. P.Michael P. Papazoglou, P.Paolo Traverso, S.Schahram Dustdar and F.Frank Leymann. Service-Oriented Computing: State of the Art and Research Challenges.Computer402007, 38-45back to text
• 24 inproceedingsN.Nuno Preguiça, J. M.Joan Manuel Marquès, M.Marc Shapiro and M.Mihai Letia. A commutative replicated data type for cooperative editing.29th IEEE International Conference on Distributed Computing Systems (ICDCS 2009)Montreal, Québec CanadaIEEE Computer Society2009, 395-403HALDOIback to text
• 25 articleY.Yasushi Saito and M.Marc Shapiro. Optimistic Replication.Computing Surveys371March 2005, 42--81URL: http://doi.acm.org/10.1145/1057977.1057980back to text
• 26 articleC.Chengzheng Sun, X.Xiaohua Jia, Y.Yanchun Zhang, Y.Yun Yang and D.David Chen. Achieving Convergence, Causality Preservation, and Intention Preservation in Real-Time Cooperative Editing Systems.ACM Transactions on Computer-Human Interaction51March 1998, 63--108URL: http://doi.acm.org/10.1145/274444.274447back to text