Contributions à la réplication de données dans les systèmes distribués à grande échelle

Data replication is a key mechanism for building a reliable and efficient data management system. Indeed, by keeping several replicas for each piece of data, it is possible to improve durability. Furthermore, well-placed copies reduce data accesstime. However, having multiple copies for a single piece of data creates consistency problems when the data is updated. Over the last years, I made contributions related to these three aspects: data durability, data access performance and data consistency. RelaxDHT and SPLAD enhance data durability by placing data copies smartly. Caju, AREN and POPS reduce access time by improving data locality and by taking popularity into account. To enhance data lookup performance, DONUT creates efficient shortcuts taking data distribution into account. Finally, in the replicated database context, Gargamel parallelizes independent transactions only, improving database performance and avoiding aborting transactions. My research has been carried out in collaboration with height PhD students, four of which have defended. In my future work, I plan to extend these contributions by (i) designing a storage system tailored for MMOGs, which are very demanding, and (ii) designing a data management system that is able to re-distribute data automatically in order to scale the number of servers up and down according to the changing workload, leading to a greener data management.La réplication de données est une technique clé pour permettre aux systèmes de gestion de données distribués à grande échelle d'offrir un stockage fiable et performant. Comme il gère un nombre suffisant de copies de chaque donnée, le système peut améliorer la pérennité. De plus, la présence de copies bien placées réduit les temps d'accès. Cependant, cette même existence de plusieurs copies pose des problèmes de cohérence en cas de modification. Ces dernières années, mes contributions ont porté sur ces trois aspects liés à la réplication de données: la pérennité des données, la performance desaccès et la gestion de la cohérence. RelaxDHT et SPLAD permettent d'améliorer la pérennité des données en jouant sur le placement des copies. Caju, AREN et POPS permettent de réduire les temps d'accès aux données en améliorant la localité et en prenant en compte la popularité. Pour accélérer la localisation des copies, DONUT crée des raccourcis efficaces prenant en compte la distribution des données. Enfin, dans le contexte des bases de données répliquées,Gargamel permet de ne paralléliser que les transactions qui sont indépendantes, améliorant ainsi les performances et évitant tout abandon de transaction pour cause de conflit. Ces travaux ont été réalisés avec huit étudiants en thèse dont quatre ont soutenu. Pour l'avenir, je me propose d'étendre ces travaux, d'une part en concevant un système de gestion de données pour les MMOGs, une classe d'application particulièrement exigeante; et, d'autre part, en concevant des mécanismes de gestion de données permettant de n'utiliser que la quantité strictement nécessaire de ressources, en redistribuant dynamiquement les données en fonction des besoins, un pas vers une gestion plus écologique des données

Performance analysis of content discovery for ad-hoc tactile networks

Tactile Internet evolves communications to encompass sensory information such as smell and haptic sensations combining ultra-low latency with extremely high availability, reliability, and security. Tactile Internet is realized through underpinning technologies such as Multi-access Edge and Fog computing which facilitate decentralized infrastructures and machine to machine (M2M) communications. Mobile ad-hoc networks (MANETs) form the foundation layer of such infrastructures, enabling direct communication between autonomous and decentralized devices such as sensors and vehicles. Among other applications, autonomous ad hoc vehicular networks (VANETs) and vehicle to vehicle (V2V) communications require efficient content discovery and quality of data transfer. The mobility patterns of vehicles within this communication model could effect the quality of data exchanged between devices in a tactile network. Several mobility models exist describing mobility patterns of mobile users in MANETs. In this paper, we present a first performance study to evaluate the impact of different mobility models on content discovery techniques for tactile Internet comprising of fast-moving vehicles and devices. This study combines direct and derived mobility metrics evaluating impact on content discovery and content dissemination using NS-3. Our simulation results indicate that unstructured techniques may not scale well within a tactile network of fast moving vehicles while maintaining low latency and could suffer from performance degradation in a saturated environment. Furthermore, simulation results also demonstrate the resilience of the unstructured content discovery protocol in mobility scenarios with proactive routing and diverse behavior

Science in a Digital Society

This report describes the main rational, objectives and outcomes of an institutional workshop - deliverable of the Action SIDSO (14099) for 2011 co- organised with the Anticipation at JRC Action and The Calouste Gulbenkian Foundation in Lisbon. The workshop explored in an anticipatory mode how current and emergent ICT will affect the conduct of scientific research in the future. Presentations and discussions focused on specific aspects related to emergent methods for engaging society and publics on scientific issues, new approaches for data sharing, mass computing, sharing of analytical tools, evaluating results and disseminating findings. Attention was also paid to impacts and security aspects associated with those approaches, namely related to scientific data and tools access, dissemination and deployment. The workshop recommended a number of fields where more thorough attention needs to be given.JRC.G.6-Digital Citizen Securit

A Novel Multi-View Table Tennis Umpiring Framework

This research investigates the development of a low-cost multi-view umpiring framework, as an alternative to the current expensive systems that are almost exclusively restricted to elite professional sports. Table tennis has been selected as the testbed because, while automating the process is challenging, it has many different complex match elements including the service, return and rallies, which are governed by a strict set of regulations. The focus is mainly on the rally element rather than the whole match. Ball detection and tracking in video frames are undertaken to determine reliably the ball position relative to key reference objects like the table surface and net, and the ball’s flight path is used to determine the rally’s status. While a low-cost option has benefits, it is technically challenging due to the limited number of cameras and generally low video resolution used. This thesis presents a portable multi-view umpiring framework that identifies each state change in a rally. It makes three significant contributions to knowledge: i) a reliable ball detection strategy that accurately detects the location of the ball in low-resolution sequences; ii) a novel framework for ball tracking using a multi-view system, and iii) a new state-machine based evaluation system for analysing table tennis rallies. In a series of ten different test scenarios, the system achieved an average of 94% system detection rate and 100% accurate decisions. A test sequence of duration 1 s can be processed in 8 s, leading to a delay of only 7 s, which is considered acceptable for practical purposes. This solution has the potential to reform the way matches are umpired, providing objectivity in resolving disputed decisions. It affords an economic technology for amateur players, while the multi-view facility is extendible to other relevant ball-based sports. Finally, the ball flight path analysis mechanism can be a valuable training tool for skills development

Unchaining Collective Intelligence for Science, Research and Technology Development by Blockchain-Boosted Community Participation

Since its launch just over a decade ago by the cryptocurrency Bitcoin, the distributed ledger technology (DLT) blockchain has followed a breathtaking trajectory into manifold application spaces. This paper analyses how key factors underpinning the success of this ground-breaking “internet of value” technology, such as staking of collateral (“skin in the game”), competitive crowdsourcing, crowdfunding, and prediction markets, can be applied to substantially innovate the legacy organization of science, research and technology development (RTD). Here, we elaborate a highly integrative, community-based strategy where a token-based crypto-economy supports finding best possible consensus, trust and truth through adding unconventional elements known from reputation systems, betting, secondary markets and social networking. These tokens support the holder’s formalized reputation, and are used in liquid-democracy style governance and arbitration within projects or community-driven initiatives. This participatory research model serves as a solid basis for comprehensively leveraging collective intelligence by effectively incentivizing contributions from the crowd, such as intellectual property (IP), work, validation, assessment, infrastructure, education, assessment, governance, publication, and promotion of projects. On the analogy of its current blockbusters like peer-to-peer structured decentralized finance (“DeFi”), blockchain technology can seminally enhance the efficiency of science and RTD initiatives, even permitting to fully stage operations as a chiefless Decentralised Autonomous Organization (DAOs)

Scalable Internet auctions

Current Internet based auction services rely, in general, on a centralised auction server; applications with large and geographically dispersed bidder client bases are thus supported in a centralised manner. Such an approach is fundamentally restrictive as too many users can overload the server, making the whole auction process unresponsive. Further, such an architecture can be vulnerable to server's failures, if not equipped with sufficient redundancy. In addition, bidders who are closer to the server are likely to have relatively faster access to the server than remote bidders, thereby gaining an unfair advantage. To overcome these shortcomings, this thesis investigates ways of enabling widely distributed, arbitrarily large number of auction servers to cooperate in conducting an auction. Allowing a bidder to register with anyone of the auction servers and place bids there, coupled with periodic exchange of auction information between servers forms the basis of the solution investigated to achieve scalability, responsiveness and fairness. Scalability and responsiveness are achieved since the total load is shared amongst many bidder servers; fairness is achieved since bidders are able to register with their local servers. The thesis presents the design and implementation of an hierarchically structured distributed Internet auction system. Protocols for inter-server cooperation are presented. Each server may be replicated locally to mask node failures. Performance evaluations of centralised and distributed configurations are performed to show the advantages of the distributed configuration over the centralised one.EThOS - Electronic Theses Online ServiceIranian Ministry of Science, Research and Technology : Isfahan UniversityGBUnited Kingdo

Electronic Imaging & the Visual Arts. EVA 2015 Florence

Information Technologies of interest for Culture Heritage are presented: multimedia systems, data-bases, data protection, access to digital content, Virtual Galleries. Particular reference is reserved to digital images (Electronic Imaging & the Visual Arts), regarding Cultural Institutions (Museums, Libraries, Palace – Monuments, Archaeological Sites). The International Conference includes the following Sessions: Strategic Issues; New Technologies & Applications; New 2D-3D Technical Developments & Applications; Virtual Galleries – Museums and Related Initiatives; Access to the Culture Information. Two Workshops regard: International Cooperation; Innovation and Enterprise