Self-Healing Protocols for Connectivity Maintenance in Unstructured Overlays

In this paper, we discuss on the use of self-organizing protocols to improve the reliability of dynamic Peer-to-Peer (P2P) overlay networks. Two similar approaches are studied, which are based on local knowledge of the nodes' 2nd neighborhood. The first scheme is a simple protocol requiring interactions among nodes and their direct neighbors. The second scheme adds a check on the Edge Clustering Coefficient (ECC), a local measure that allows determining edges connecting different clusters in the network. The performed simulation assessment evaluates these protocols over uniform networks, clustered networks and scale-free networks. Different failure modes are considered. Results demonstrate the effectiveness of the proposal.Comment: The paper has been accepted to the journal Peer-to-Peer Networking and Applications. The final publication is available at Springer via http://dx.doi.org/10.1007/s12083-015-0384-

The environmental impact of the consumption of fishery and aquaculture products in France

In the context of climate change, diet is a key driver of environmental impacts. Previous research has emphasized the environmental benefit of increasing consumption of fishery and aquaculture products (FAPs) in Europe. However, increasing the proportion of FAPs in consumer diets could also lead to a transfer of environmental damage from earth to sea. It is thus important to evaluate the environmental impacts of FAPs on marine ecosystems globally. For that purpose, an original database characterizing the origin of FAPs consumed in France has been constructed, and matched to indicators of environmental impact. Use of the database revealed that the FAPs in the French diets (1.7 Mt live weight) had a corresponding primary production required (PPR) worth 1252 Mt, with an impact per ton of product live weight worth 2622 kg CO2 eq. for climate change, 18 kg PO(4)(3)(-)eq. for eutrophication, and 26,604 MJ for energy use. Some heterogeneity across species was found, implying that the species composition of the FAPS consumed had a strong influence on environmental footprint. Furthermore, production methods also substantially affect global impact. The results show that, among FAPS consumed in France, trawled crustaceans and farmed shrimps or prawns are the greatest contributors to global warming (27,800 and 13,344 kg CO2 eq. per ton live weight, respectively), despite good performances regarding trophic level based ecosystem indicators (a PPR of 3 and 9 Mt respectively). Shellfish register the smallest footprint both globally and at ecosystem level (545 kg CO2 eq., 1 kg PO43- eq., 10,414 MJ, and a PPR of 5 Mt per ton live weight). Our result suggest that, to avoid a transfer of environmental burden from land to sea, policies aimed at promoting consumption of FAPs in European diets should be refined to take account of differential impacts across species, origin and production methods of those FAPs. (C) 2021 Elsevier Ltd. All rights reserved.Peer reviewe

Using language technologies to support individual formative feedback

In modern educational environments for group learning it is often challenging for tutors to provide timely individual formative feedback to learners. Taking the case of undergraduate Medicine, we have found that formative feedback is generally provided to learners on an ad-hoc basis, usually at the group, rather than individual, level. Consequently, conceptual issues for individuals often remain undetected until summative assessment. In many subject domains, learners will typically produce written materials to record their study activities. One way for tutors to diagnose conceptual development issues for an individual learner would be to analyse the contents of the learning materials they produce, which would be a significant undertaking. CONSPECT is one of six core web-based services of the Language Technologies for Lifelong Learning (LTfLL) project. This European Union Framework 7-funded project seeks to make use of Language Technologies to provide semi-automated analysis of the large quantities of text generated by learners through the course of their learning. CONSPECT aims to provide formative feedback and monitoring of learners’ conceptual development. It uses a Natural Language Processing method, based on Latent Semantic Analysis, to compare learner materials to reference models generated from reference or learning materials. This paper provides a summary of the service development alongside results from validation of Version 1.0 of the service

The pragmatic proof: hypermedia API composition and execution

Machine clients are increasingly making use of the Web to perform tasks. While Web services traditionally mimic remote procedure calling interfaces, a new generation of so-called hypermedia APIs works through hyperlinks and forms, in a way similar to how people browse the Web. This means that existing composition techniques, which determine a procedural plan upfront, are not sufficient to consume hypermedia APIs, which need to be navigated at runtime. Clients instead need a more dynamic plan that allows them to follow hyperlinks and use forms with a preset goal. Therefore, in this paper, we show how compositions of hypermedia APIs can be created by generic Semantic Web reasoners. This is achieved through the generation of a proof based on semantic descriptions of the APIs' functionality. To pragmatically verify the applicability of compositions, we introduce the notion of pre-execution and post-execution proofs. The runtime interaction between a client and a server is guided by proofs but driven by hypermedia, allowing the client to react to the application's actual state indicated by the server's response. We describe how to generate compositions from descriptions, discuss a computer-assisted process to generate descriptions, and verify reasoner performance on various composition tasks using a benchmark suite. The experimental results lead to the conclusion that proof-based consumption of hypermedia APIs is a feasible strategy at Web scale.Peer ReviewedPostprint (author's final draft

Reliable Composite Web Services Execution: Towards a Dynamic Recovery Decision

AbstractDuring the execution of a Composite Web Service (CWS), different faults may occur that cause WSs failures. There exist strategies that can be applied to repair these failures, such as: WS retry, WS substitution, compensation, roll-back, or replication. Each strategy has advantages and disadvantages on different execution scenarios and can produce different impact on the CWS QoS. Hence, it is important to define a dynamic fault tolerant strategy which takes into account environment and execution information to accordingly decide the appropriate recovery strategy. We present a preliminary study in order to analyze the impact on the CWS total execution time of different recovery strategies on different scenarios. The experimental results show that under different conditions, recovery strategies behave differently. This analysis represents a first step towards the definition of a model to dynamically decide which recovery strategy is the best choice by taking into account the context-information when the failure occurs

Eighth Workshop and Tutorial on Practical Use of Coloured Petri Nets and the CPN Tools, Aarhus, Denmark, October 22-24, 2007

This booklet contains the proceedings of the Eighth Workshop on Practical Use of Coloured Petri Nets and the CPN Tools, October 22-24, 2007. The workshop is organised by the CPN group at the Department of Computer Science, University of Aarhus, Denmark. The papers are also available in electronic form via the web pages: http://www.daimi.au.dk/CPnets/workshop0