Secured replication in peer-to-peer collaborative systems – PhD Defense Victorien Elvinger

A collaborative application allows multiple users to edit a shared content.
Collaborative peer-to-peer environments aim to design applications with
desirable properties: high-availability, low-latency, fault-tolerance,
and scalability.
Every peer (user) modifies her own copy of the content.
Concurrent modifications of the copies lead to their divergence.
Replication protocols are responsible for the convergence of copies.

These protocols assume the absence of malicious peers that compromise
the convergence of copies.
Can we secure the convergence of copies and preserve the properties of
collaborative peer-to-peer environment?
We propose two protocols to secure convergence.
The first protocol maintains a replicated and unforgeable log that
stores the modifications of the content.
Peers preserve the full log in order to foil the attacks of malicious
peers and to transmit it to new peers.
The second protocol enables the peers to truncate their log.
The log truncation relies on the concept of Stability.
A modification becomes stable once every modification added in the log
depends on it.
To join the collaboration, a peer retrieves a copy of
the content and a truncated log used for checking the copy authenticity.

A Conflict-free Replicated Data Type (CRDT) encapsulates a replication
Sequence CRDTs generally assume the integration of content modifications
in a causal order.
A delayed integration propagates slowness across the system.
The connection of a peer may lead to the integration of multiple
Can we remove these delays and these costly integrations?
We formalize a family of sequence CRDTs and we propose their
synchronization using delta states.
Delta states can be integrated in any order.
They are able to summarize several modifications.
We propose a sequence CRDT that takes advantage of our approach.


Emmanuelle Anceaume, directrice de recherche IRISA
Pascal Molli, professeur à l’Université de Nantes

Steve Kremer, directeur de recherche Inria Grand Est
Esther Pacitti, professeure à l’Université de Montpellier 2

François Charoy, professeur à l’Université de Lorraine
Gérald Oster, maître de conférence à l’Université de Lorraine

Soutenance de HDR – Claudia Ignat – 23/04 à 15h

Large-scale trustworthy distributed collaborative systems


Most existing collaborative systems rely on a central authority and
place personal information in the hands of a single large corporation
which is a perceived privacy threat. Moreover, these systems do not
scale well in terms of the number of users and their modifications. My
research work aims to move away from centralized authority-based
collaboration towards a large scale trust-based peer-to-peer
collaboration where control over data is given to users who can decide
with whom to share their data. The main advantages of peer-to-peer
collaborative systems are high scalability and resilience to faults and

First, I describe my contributions to the design and evaluation of
optimistic data replication algorithms. I also present my work on group
awareness specifically on what information should be provided to users
to prevent conflicting changes and to understand divergence when
conflicts cannot be avoided.

Secondly, I describe my contributions on large scale trustworthy
collaboration. I present a contract-based collaboration model where
contracts are specified by the data owners when they share the data and
user trust is assessed according to the observation of adherence to or
violation of contracts. For testing the proposed trust-based
collaboration model, I designed a user experiment employing trust game
and relying on a computational trust metric according to user exchanges
in this game.

Finally, I present my future research directions on secure and
trustworthy collaborative data management.

Keywords: distributed collaborative systems, operational transformation,
CRDT, group awareness, trust, contract-based collaboration,
authenticated logs, trust game, user studies

More details are available here:

Jury members
Prasun DEWAN, Professor at University of North Carolina at Chapel Hill
Valerie ISSARNY, Director of research at Inria
François TAIANI, Professor at Université de Rennes I

Sihem AMER-YAHIA, Director of research at CNRS
François CHAROY, Professor at Université de Lorraine
Isabelle CHRISMENT, Professor at Université de Lorraine
Fabien GANDON, Director of research at Inria
Pascal MOLLI, Professor at Université de Nantes

PhD Defense 3-2-2021 – Béatrice Linot – La confiance dans les situations de travail collaboratifs médiatisés par des environnements numériques

Beatrice will present her work the 3/2/2021 2pm in front of

Myriam Lewkowicz – Université de Technologie de Troyes
Franck Ganier – Université Bretagne Occidentale, LABSTICC
Caroline Rizza – Telecom Paris
Aurélie Montarnal  – École des Mines d’Albi-Carmaux\
Valérie L. Shalin – Wright State University



France has experienced several disasters in the last decade: Floods (Var, Alpes Maritimes (2015), Seine basin and Loire (2016) ; Storms Lothar, Martin (1999), Klaus (2009), Xynthia (2010) ; Terrorist attacks, Charlie Hebdo and Bataclan (2015), Nice (2016). All of these events have common properties: they are all unexpected. The resulting disorganization puts a premium on communication between different specialties (e.g. Police, firefighters, medical technicians etc.). Crisis involves a number of actors and poses important problems of communication and comprehension between them, in addition to technical difficulty. Crisis necessitates the establishment of distributed cooperative activities and mediation between teams that are unfamiliar with each other and have different experiences, expertise, cultures and organizations. Communication between specialties is essential  and  agree with this emphasis on communication, but enrich our understanding of the problem. Groupware systems aim to provide participants with common awareness, i.e., information about the presence, activities, and availability of the other participants in the same system. Independent of the software, recent analyses show that trust between partners is crucial during crisis management. Yet empirical studies in several domains (e.g., e-banking, civil security, healthcare, military, industries, etc.) reveal low participant confidence in these systems. Additionally, low confidence generates inappropriate behavior (e.g., altering and degrading performance technology users) reducing use, thereby affecting efficiency. The French tool CRISORSEC is intended to support information sharing among crisis actors. Yet, users question its utility, its form, its uses, its limits and its possible perverse effects. We suggest that understanding performance in different situations informs design requirements. In this thesis, we contribute towards addressing the aforementioned challenges. Specifically, the main contributions of this thesis are as follows:

– We propose a new model, Computer-supported Crisis Management Communication (3 C) to capture communication during crisis management when communication is mediated by computational tools.
– Combining theory and methods used in psychology, human factors, with computer science we propose to determine how and why trust and communication is degraded in relation to civil security.
–  Finally, we propose

design guidelines for digital devices that promote the sharing of information for the purpose of developing and maintaining shared situational awareness during collaborative activities.

We propose multi-level factors influencing trust and behavior of the operators during collaborative activities supported by computers (e.g., contextual factors, organizational factors, individual factors,) and particularly during information sharing. This permits the identification of elements necessary to recreate links broken by the computer in order to design tools offering conditions of trust in the framework of collaborative information sharing. The different contributions of the proposed approach are demonstrated and validated analytically and empirically through experimental results.

PhD Defense 14-1-2020 – Hoai Le Nguyen – Étude des conflits dans l’édition collaborative

Collaborative Editing (CE) has long captured the attention of Computer-supported-cooperative work (CSCW) researchers. Early researches about CE (in the 1990s and the early 2000) focused on describing different characteristics of CE based on interviewing people who had participated in some CE projects.
Some recent researches about CE started analyzing the logs of CE activities to study how people edit together with support of modern CE tools such as Git version control systems and Google Docs.

From the general view point, the process of CE is the continuous synchronization of `multiple, parallel streams of activity’ of collaborators. If the synchronization takes place less often, for example the development of a software project based on Git version control system, it is considered as `asynchronous’ work mode. And if the synchronization takes place within a small interval, for example editing a shared document in ShareLaTex, it is considered as `synchronous’ work mode.
The longer the divergence is, more conflicts are likely to happen during the synchronization.
Resolving conflicts is costly, especially after a long period of divergence. Understanding how often conflicts happen and how do user resolve conflict in real CE projects is important to ensure good performance and user experience in collaborative editing.
In the first part of this thesis, we borrow the collaboration traces of four large open source projects in Git version control system to conduct our analysis. We analyze different types of textual conflicts that arise during the development and how developers resolve these types of conflict. In particular regarding `adjacent-lines conflicts’, we found that users mostly resolve them by applying changes from both sites. Besides, we also analyze how often users use `roll-back to previous version’ as a way to resolve merge conflict.

The process of CE based on online collaborative editor is more specific. It can be split into several  `sessions’ of editing which are performed by a single author or several authors. They are denoted as `single-authored session’ and  `co-authored session’ respectively. This fragmentation process requires a predefined `interval’ or `maximum time gap’ which is not yet well defined in previous studies. In the second part of this thesis, we analyze the logs of CE works of students of an Engineering School using ShareLaTeX which were collected and anonymized for privacy purpose. By examining different `maximum time gaps’ from 30 seconds to 15 minutes on the logs we found that we can determinate a suitable `maximum time gap’ to split CE activities into sessions by evaluating the distribution of the `external-distance’.
Besides, we analysed the editing activities inside each `co-author sessions’. We borrow a [30 seconds, 10 characters] time-position window to examine these `potential conflict’ cases. The result shows that people rarely edit closely in both time-position. However, conflicts are more likely to happen in these cases.

PhD Defense 12-1-2020 : Quentin Laporte-Chabasse – Étude morpho-statistique des réseaux sociaux. Application aux collaborations inter-organisationnelles.


Decentralised collaborative applications address privacy, availability and security issues related to centralised collaborative platforms. Such applications are based on a peer-to-peer communication paradigm according to which all users are directly connected to one another. Collaborations tend to widen and spread beyond the borders of organisations. Under these circumstances, it is necessary to guarantee to users the control over their data, while keeping collaboration available. To that end, the social network that has built between collaborators may be used as topology. Lack of information on this trusted network leads us to develop an approach to study its morphological properties.

In this thesis, we develop and implement an approach to study the social structure of interactions in the context of inter-organisational collaborations. We propose a stochastic approach based on \aclp{ERGM} and spatial models. We define a formalism that highlights the structure of interactions and integrates the organisational dimension. We propose to use a Bayesian inference method, ABC Shadow, to overcome the issues related to the parameters estimation. This approach is applied to a real case study: the collaborations initiated by researchers in a laboratory. In particular, it highlights the low tendency for a researcher to create collaborative links with other laboratories. We show that this approach can be applied to other kinds of social interactions, such as interactions between pupils of a primary school. Finally, we present a parallelisation strategy of the Gibbs sampler aimed at processing larger graphs in a reasonable time.

PhD defense of Guillaume Rosinosky – Elasticity and BPMaaS – 23-1-2019

 Wednesday, January 23 2019 at 14:00 in room A008 in the LORIA.
The jury is composed of :
Walid Gaaloul – full professor at Telecom Sud Paris
Salima Benbernou – full professor at Université Paris Descartes (absent)
Malika Smail – associate professor at Université de Lorraine, LORIA
Parisa Ghodous – full professor at Université Lyon I, LIRIS
Duy Tran Quang – manager at Bonitasoft
François Charoy – full professor at Université de Lorraine, LORIA
Samir Youcef – associate professor at Université de Lorraine, LORIA
The availability of middleware platforms in the cloud, with “transparent” scalability, is a  progress for software developers and integrators. They can develop and deploy their applications without worrying about technical details.
However, the exploitation cost of a cloud infrastructure can quickly become important. Providers requires methods to reduce this cost by adapting the size of ressources to the needs of the customers. In this thesis, we focus on multi-tenant transactional web applications, more precisely on business processes execution engines. We propose methods allowing to optimize the operational costs of providers of business process execution “as a Service”  (BPMaaS) while ensuring a sufficient level of quality of service. This type of application do not scale well because of its persistence tier and of the transactional nature of operations. One must distribute the customers installations in order to optimize the cost, and sometimes move them depending of the needs of the customers.
These moves (or migrations) have an impact on the quality of service and they must be limited. First, we propose a method for measuring the size of resources in terms of  BPM tasks throughput, and then a method for measuring the impact of migrations we  evaluate, thus confirming our hypothesis. We also propose several linear optimization models and heuristics targeting resouce allocation and distribution of customers, while limiting the number of migrations. These models are based on the knowledge of the needs of  customers per time slot. We have experimented our three methods on the BPM solution Bonita, and demonstrated that they provide substantial savings on the infrastructure exploitation compared to a basic method.

ICSOC 2018 paper presentation by Guillaume Rosinosky

A Genetic Algorithm for Cost-Aware Business Processes Execution in the Cloud

Quentin Laporte Chabasse et Victorien Elvinger at 4th IEEE International Conference on Collaboration and Internet Computing

Quentin Laporte Chabasse and  Victorien Elvinger are at the 4th IEEE International Conference on Collaboration and Internet Computing to present our work

Link-Sign Prediction in Dynamic Signed Directed Social Networks
Quang-Vinh Dang and Claudia-Lavinia Ignat (Universite ́de Lorraine)

Claudia-Lavinia Ignat is doing a Keynote at CRIWG conference 2018

CRIWG 2018

24th International Conference on Collaboration and Technology

Costa de Caparica, Portugal — September 5-7, 2018

From group to large scale trustworthy distributed collaborative systems

From cognitive psychology to Trust Theory – by Siavash Atarodi – 30/3/2018 – B013

Seminar by Siavash Atarodi

From cognitive psychology to Trust Theory

This thesis, which was part of a European research project, focuses on the problem of the reluctance of elderly people to use ICTs. More specifically, it focuses on the psychosocial factors that influence the attitudes of people aged 62 and over towards ICTs. We conducted six studies in this framework, divided into two areas. The first axis, including two studies, adresses public strategies and practices for orienting older people towards ICTs. In the first one we analyzed the practices of the organizations involved in the orientation of the elderly towards gerontechnologies in the Lorraine region of France. It emerges that the access routes are very different according to the counties and communities, but also according to the first interlocutor requested by the elderly person and his / her relatives. The second study aimed to analyze public strategies and regulations encouraging and facilitating the use of ICT­ based services for the elderly in six regions of Europe. Different stages of development of these strategies emerged and a north / south lag was observed. In the second axis, with four studies, we examined from different angles the factors influencing the attitudes of the elderly towards ICTs. Our third study addressed the perceptions of older persons regarding ICTs and their perceived needs. We identified 22 perceptual items divided into eight components forming a scale of perceptions of ICTs as well as a scale of perceived needs including two components. The fourth study assessed the impact of previous experience with ICTs on perceptions of ICTs. We carried out analyzes of the variance of ICT perceptions depending on whether a computer was owned or not and the follow­up of computer literacy courses. The results showed that computer ownership and course tracking were associated with significantly more positive perceptions of ICTs. The fifth study analyzed the impact of the region of residence on perceptions of ICTs. We compared the perceptions of the elderly in six regions of the EU. We found coherence between public strategies for orienting older people to ICTs and the perceptions of older people regarding ICTs. Finally, our latest study focused on the analysis of factors influencing attitudes toward ICTs for different types of activities. Depending on the dependent variable, different factors were found, including perceptions of ICTs, perceived needs, prior experience, region of residence and socio­demographic variables.