2023Activity reportProject-TeamCOAST

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  25 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)  28 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  27 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  18
• algorithms based on commutative replicated data types (CRDT)  26.

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 24, 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 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  15.

Recently, we also proposed new approaches for augmenting business processes. By relying mainly on data analysis, machine learning algorithms, and complex event processing, we exploited the data generated by business process execution (event data, event logs) and improved these processes from different perspectives such as instance scheduling and event management in an IoT environment 20.

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 and with the PhD thesis of Lisa Formentini who will study the impact of the COVID lockdown on firefighters work practices and ecology of artefacts.

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. In this context, in order to decrease the overhead of the replicated data structure, we proposed a CRDT for Sequence which embeds a renaming mechanism 23. The domain of collaborative editing requires us to consider the problem of access control of participants 11 and group key management 10.

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 algorithms 7 and on group key management 10 for IPFS (InterPlanetary File System) peer-to-peer storage and we will transfer it to hive.

6.1 New software

7.1 Distributed Access Control using CRDTs

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

Existing access control mechanisms mainly based on a central authority feature several difficulties in the context of collaborative systems. In the case of a federation of organizations, agreeing on an authority that manages the access rights is almost impossible. The lack of a central authority raises issues of group management such as joining and leaving the group as well as rights revocation. Indeed, it should be possible for a partner to revoke granted rights without contacting an external authority. Moreover, current access control mechanisms feature performance issues that are critical for real-time collaboration when the number of updates is high. Indeed, delays are too high for sending at each user action an access request and waiting for its answer from a trusted central authority which maintains the security policies. In order to avoid the use of a central server that stores all data, we propose that access rights as well as data are replicated.

We proposed CRDT algorithms for the synchronisation of access rights that were composed with CRDT algorithms for data synchronisation. In the face of concurrent edits on the access rights and the document, conflicts are likely to occur. For instance, users might execute operations on the document while their rights of executing these operations are concurrently revoked. An important feature of collaborative applications is to allow multiple dynamic administrators that can modify users access rights (e.g. read or write) to the shared documents. In the face of dynamic groups of administrators conflicts might get complex. For instance, an administrator might assign an access right to a user, while concurrently this administrator right is removed. We proposed a replicated access control mechanism that manages a collaborative document with multiple, dynamic administrators. Besides maintaining consistency over the replicated document state and access rights, our CRDT solution preserves document integrity and prevents unauthorized modifications. An a posteriori enforcement is provided in order to correct the document state by compensating the effect of unauthorized modifications. Based on causality mechanisms, operations on document are mapped to intervals of authorisations where a right is enabled or disabled. This allows us to generate the appropriate compensations to the document state even after unauthorized operations have been integrated 11.

7.2 CRDTs for Mutable Data in Peer-to-peer Storage Systems

Participants: Quentin Acher, Claudia-Lavinia Ignat, Shadi Ibrahim.

The continuous growth in data volume increases the interest in using peer-to-peer systems not only to store static data (i.e., immutable data) but also to store and share mutable data – data that are updated and modified by multiple users. Unfortunately, current peer-to-peer systems are mainly optimized to manage immutable data. Thus, each modification creates a new copy of the file, which leads to a high useless network usage.

Conflict-free Replicated Data Types (CRDTs) are specific data types built in a way that mutable data can be managed without the need for consensus-based concurrency control. In 7 we demonstrated the potential benefits of integrating CRDTs in the InterPlanetary File System (IPFS), an open-source widely used peer-to-peer content sharing system, meant to become the storage layer of the decentralized web. In an attempt to fill the gap between theory and practice, we provided the first quantitative measurement of the performance of CRDTs in IPFS. We introduced IM-CRDT (InterPlanetary Merkle-CRDT), an implementation of Merkle-CRDTs in IPFS that focuses on set data types. Experiments on Grid’5000 showed that IM-CRDT reduces the data transfer of an update by up to 99.96% and the convergence time by 54.6%-62.6%. More importantly, we find that IM-CRDT can sustain low convergence time under concurrent updates.

7.3 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 14 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.

7.4 Distributed Delivery Service for Group Key Agreement Protocols

Participants: Davide Frey, Claudia-Lavinia Ignat, Amine Ismail, Ludovic Paillat (, Mathieu Turuani.

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 a fully distributed Delivery Service 10. 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.

7.5 Ethereum’s storage enhancement

Participants: Jean-Philippe Eisenbarth, Olivier Perrin, Thibaut Cholez.

Blockchains face many challenges in time, among which the ever-growing storage needs for blockchain data. In particular, Ethereum is quickly approaching the 1 TB storage limit for a node. This may significantly reduce the candidates able to run an Ethereum fullnode.

In 2023 we proposed an elegant way to reduce the storage needs of an Ethereum node by leveraging Ethereum’s DHT (Distributed Hash Table) to distribute the storage of old blocks and receipts (what we called cold data). Indeed, Ethereum’s peer-to-peer (P2P) network is based on a well-known architecture named Kademlia that can efficiently retrieve data at the P2P network level with a logarithmic complexity. However, while fully functional, Ethereum’s DHT is under-exploited so far and only used to list contacts (known nodes) but not to store any blockchain data. To understand why, we investigated the Ethereum’s past and current storage and synchronization strategies and we explained why the distribution of the storage makes much sense today, blocks being no more executed since genesis block by a new node. We then proposed and evaluated a new synchronization strategy that takes advantage of Ethereum’s DHT wasted potential, is fully backward compatible with current clients and does not affect any core mechanism of the Ethereum blockchain. We provided an implementation of our new synchronization mechanism exploiting Ethereum’s DHT in Geth. Our evaluation on a private Ethereum instance proved the validity of the solution. When applied to an Ethereum peer, our solution saves roughly 60% of the storage of a node (360 GB) which represents a total of 12 PB of data at the network scale 8, 9.

7.6 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 experience12, 13.

8.1 Bilateral contracts with industry

9.1 National initiatives

10.1 Promoting scientific activities

10.2 Teaching - Supervision - Juries

10.3 Popularization

11.1 Major publications

• 1 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
• 2 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
• 3 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
• 4 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
• 5 inproceedingsL.Ludovic Paillat, C.-L.Claudia-Lavinia Ignat, D.Davide Frey, M.Mathieu Turuani and A.Amine Ismail. Design of an Efficient Distributed Delivery Service for Group Key Agreement Protocols.Lecture Notes in Computer Science (LNCS)FPS 2023 - 16th International Symposium on Foundations & Practice of SecurityBordeaux, FranceDecember 2023, 1-16HAL
• 6 inproceedingsG.Guillaume Rosinosky, S.Samir Youcef and F.Francois Charoy. A Genetic Algorithm for Cost-Aware Business Processes Execution in the Cloud.Lecture Notes in Computer ScienceICSOC 2018 - The 16th International Conference on Service-Oriented ComputingICSOC 2018: Service-Oriented Computing11236Hangzhou, ChinaSpringerNovember 2018, 14HAL

11.2 Publications of the year

11.3 Cited publications

• 15 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
• 16 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
• 17 inproceedingsQ. V.Quang Vinh Dang and C.-L.Claudia-Lavinia Ignat. Computational Trust Model for Repeated TrustGames. Proceedings of the 15th IEEE International Conference on Trust, Security and Privacy in Computing and Communications (TrustCom 2016) Tianjin, ChinaAugust 2016, URL: https://hal.inria.fr/hal-01351250back to text
• 18 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
• 19 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, 1-22HALDOIback to text
• 20 phdthesisA.Abir Ismaili-Alaoui. Methodology for an Augmented Business Process Management in IoT Environment.Université de Lorraine ; Université Mohammed V (Rabat)December 2022HALback to text
• 21 inproceedingsH.-L.Hoang-Long Nguyen, J.-P.Jean-Philippe Eisenbarth, C.-L.Claudia-Lavinia Ignat and O.Olivier Perrin. Blockchain-Based Auditing of Transparent Log Servers.The 32nd Annual IFIP WG 11.3 Conference on Data and Applications Security and Privacy (DBSec 2018)Proceeding of Data and Applications Security and Privacy XXXII - 32nd Annual IFIP WG 11.3 ConferenceBergamo, ItalyJuly 2018, 21-37URL: https://hal.archives-ouvertes.fr/hal-01917636back to text
• 22 inproceedingsH.-L.Hoang-Long Nguyen, C.-L.Claudia-Lavinia Ignat and O.Olivier Perrin. Trusternity: Auditing Transparent Log Server with Blockchain.Companion of the The Web Conference 2018Lyon, FranceApril 2018, 79-80URL: https://hal.inria.fr/hal-01883589DOIback to text
• 23 phdthesisM.Matthieu Nicolas. Ré-identification sans coordination dans les types de données répliquées sans conflits (CRDTs).Université de LorraineDecember 2022HALback to text
• 24 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
• 25 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
• 26 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
• 27 articleY.Yasushi Saito and M.Marc Shapiro. Optimistic Replication.Computing Surveys371March 2005, 42--81URL: http://doi.acm.org/10.1145/1057977.1057980back to text
• 28 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