Efficient Renaming in Sequence CRDTs Nicolas, Matthieu; Oster, Gerald; Perrin, Olivier
IEEE transactions on parallel and distributed systems,
2022-Dec.-1, 2022-12-1, 2022-12-01, Letnik:
33, Številka:
12
Journal Article
Recenzirano
Odprti dostop
To achieve high availability, large-scale distributed systems have to replicate data and to minimise coordination between nodes. For these purposes, literature and industry increasingly adopt ...Conflict-free Replicated Data Types (CRDTs) to design such systems. Conflict-free Replicated Data Types (CRDTs) are new specifications of existing data types, e.g., Set or Sequence. While CRDTs have the same behaviour as previous specifications in sequential executions, they actually shine in distributed settings as they natively support concurrent updates. To this end, CRDTs embed in their specification conflict resolution mechanisms. These mechanisms usually rely on identifiers attached to elements of the data structure to resolve conflicts in a deterministic and coordination-free manner. Identifiers have to comply with several constraints, such as being unique or belonging to a dense total order. These constraints may hinder the identifier size from being bounded. Identifiers hence tend to grow as the system progresses, which increases the overhead of CRDTs over time and leads to performance issues. To address this issue, we propose a novel Sequence CRDT which embeds a renaming mechanism. It enables nodes to reassign shorter identifiers to elements in an uncoordinated manner. Experimental results demonstrate that this mechanism decreases the overhead of the replicated data structure and eventually minimises it.
Summary
Wikis are one of the most important tools of Web 2.0 allowing users to easily edit shared data. However, wikis offer limited 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. Real‐time collaborative editing reduces conflicts as the time frame for concurrent work is very short. In this paper, we propose extending wiki systems with real‐time collaboration. We propose an automatic merging solution adapted for rich content wikis. Our solution relies on an operational transformation algorithm defined for high level operations that capture user actions such as move, merge, and split.
Collaboration graphs are relevant sources of information to understand behavioural tendencies of groups of individuals. The study of these graphs enables figuring out factors that may affect the ...efficiency and the sustainability of cooperative work. For example, such a collaboration involves researchers who develop relationships with their external counterparts to address scientific challenges. As relations and projects change over time, the evolution of social structures must be tackled. We propose a statistical approach considering different structural collaboration patterns and captures the dynamic of the relational structures over the years. Our approach combines spatial processes modelling and Exponential Random Graph Models used to analyse social processes. Since the normalising constant involved in classical Markov Chain Monte Carlo (MCMC) approaches is intractable, the inference remains challenging. To overcome this issue, we propose a Bayesian tool that relies on the recent ABC Shadow algorithm. The method is illustrated on real data sets from an open archive of scholarly documents. Through a simple formalism, our approach highlights the interactions between the different types of social relations at stake in the collaboration network.
A Teaching System to Learn Programming Quinson, Martin; Oster, Gérald
Proceedings of the 2015 ACM Conference on Innovation and Technology in Computer Science Education,
06/2015
Conference Proceeding
Odprti dostop
The Programmer's Learning Machine (PLM) is an interactive exerciser for learning programming and algorithms. Using an integrated and graphical environment that provides a short feedback loop, it ...allows students to learn in a (semi)-autonomous way. This generic platform also enables teachers to create specific programming microworlds that match their teaching goals. This paper discusses our design goals and motivations, introduces the existing material and the proposed microworlds, and details the typical use cases from the student and teacher point of views.
This highly practical book provides useful drawing directives to clinicians involved in the assessment and treatment of individuals, families, and groups in both inpatient and outpatient settings. ...The authors present many case histories to show how the various aspects of drawing techniques can be integrated and applied in clinical practice. "Using Drawings in Assessment and Therapy" is vividly illustrated with over 90 drawings, which are used to describe how the therapeutic interaction can be enhanced by adding this method to the clinician's repertoire.
This second edition condenses and synthesizes a variety of drawing directives that aid clinicians in the assessment process and in therapy. It also features updated literature reviews, with new case studies and accompanying art work. All therapists who are involved or interested in art therapy will gain a wealth of information, insight, and practical tips from this thorough volume.
The ever growing request for digital information raises the need for content distribution architectures providing high storage capacity, data availability and good performance. While many simple ...solutions for scalable distribution of quasi-static content exist, there are still no approaches that can ensure both scalability and consistency for the case of highly dynamic content, such as the data managed inside wikis. We propose a peer-to-peer solution for distributing and managing dynamic content, that combines two widely studied technologies: Distributed Hash Tables (DHT) and optimistic replication. In our “universal wiki” engine architecture (UniWiki), on top of a reliable, inexpensive and consistent DHT-based storage, any number of front-ends can be added, ensuring both read and write scalability, as well as suitability for large-scale scenarios.
The implementation is based on Damon, a distributed AOP middleware, thus separating distribution, replication, and consistency responsibilities, and also making our system transparently usable by third party wiki engines. Finally, UniWiki has been proved viable and fairly efficient in large-scale scenarios.
Distributed groupware systems provide computer support for manipulating objects such as a text document or a filesystem, shared by two or more geographically separated users. Data replication is a ...technology to improve performance and availability of data in distributed groupware systems. Indeed, each user has a local copy of the shared objects, upon which he may perform updates. Locally executed updates are then transmitted to the other users. This replication potentially leads, however, to divergent (i.e. different) copies. In this respect, Operational Transformation (OT) algorithms are applied for achieving convergence of all copies, i.e. all users view the same objects. Using these algorithms users can exchange their updates in any order since the convergence should be ensured in all cases. However, the design of such algorithms is a difficult and error-prone activity since building the correct updates for maintaining good convergence properties of the local copies requires examining a large number of situations. In this paper, we present the modelling and deductive verification of OT algorithms with algebraic specifications. We show in particular that many OT algorithms in the literature do not satisfy convergence properties unlike what was stated by their authors.
Abstract
Respiratory syncytial virus (RSV) infection is the most common cause of lower respiratory tract infection and the leading cause of hospitalization among young children, incurring high annual ...costs among US children under the age of 5 years. Palivizumab has been found to be effective in reducing hospitalization and preventing serious lower respiratory tract infections in high-risk infants. This paper presents a systematic review of the cost-effectiveness studies of palivizumab and describes the main highlights of a round table discussion with clinical, payer, economic, research method, and other experts. The objectives of the discussion were to (1) review the current state of clinical, epidemiology, and economic data related to severe RSV disease; (2) review new cost-effectiveness estimates of RSV immunoprophylaxis in US preterm infants, including a review of the field’s areas of agreement and disagreement; and (3) identify needs for further research.
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