A Generic API for Load Balancing in Structured P2P Systems

International audienceReal world datasets are known to be highly skewed, often leading to an important load imbalance issue for distributed systems managing them. To address this issue, there exist almost as many load balancing strategies as there are different systems. When designing a scalable distributed system geared towards handling large amounts of information, it is often not so easy to anticipate which kind of strategy will be the most efficient to maintain adequate performance regarding response time, scalability and reliability at any time. Based on this observation, we describe the methodology behind the building of a generic API to implement and experiment any strategy independently from the rest of the code, prior to a definitive choice for instance. We then show how this API is compatible with famous existing systems and their load balancing scheme. We also present results from our own distributed system which targets the continuous storage of events structured according to the Semantic Web standards, further retrieved by interested parties. As such, our system constitutes a typical example of a Big Data environment

Modular P2P-Based Approach for RDF Data Storage and Retrieval

International audienceOne of the key elements of the Semantic Web is the Resource Description Framework (RDF). Efficient storage and retrieval of RDF data in large scale settings is still challenging and existing solutions are monolithic and thus not very flexible from a software engineering point of view. In this paper, we propose a modular system, based on the scalable Content-Addressable Network (CAN), which gives the possibility to store and retrieve RDF data in large scale settings. We identified and isolated key components forming such system in our design architecture. We have evaluated our system using the Grid'5000 testbed over 300 peers on 75 machines and the outcome of these micro-benchmarks show interesting results in terms of scalability and concurrent queries

Componentising a scientific application for the grid

CoreGRID is a Network of Excellence funded by the European Commission under the Sixth Framework Programm

Évaluation d'une architecture de stockage RDF distribuée

Atelier "Ontologies et Jeux de Données pour évaluer le web sémantique (OJD)"Stocker des informations du web sémantique implique d'être capable de pouvoir potentiellement gérer de très importants volumes de données. D'où le besoin d'opter pour une solution forcément distribuée, entre autres de type pair-à-pair, pour pouvoir passer à l'échelle. Un système de stockage RDF réparti requiert de mettre en place un algorithme particulier pour la résolution des requêtes SPARQL. Les données étant distribuées à travers un réseau de pairs, il est nécessaire d'exécuter une partie de la requête sur certains de ces pairs, puis d'agréger et d'appliquer d'éventuelles conditions de filtrage sur les différents résultats intermédiaires obtenus, avant de pouvoir retourner les résultats finaux. Il existe actuellement une douzaine de benchmarks pour le RDF, mais aucun d'entre eux ne se présente comme étant pensé pour s'adapter à une architecture de stockage réparti. Dans cet article, nous mettons en évidence le nombre de résultats intermédiaires générés par les requêtes SPARQL, un aspect important dans un contexte distribué, et qui nous semble à l'heure actuelle négligé par les benchmarks pour le RDF

RDF Data Indexing and Retrieval: A survey of Peer-to-Peer based solutions

The Semantic Web enables the possibility to model, create and query resources found on the Web. Enabling the full potential of its technologies at the Internet level requires infrastructures that can cope with scalability challenges and support various types of queries. The attractive features of the Peer-to-Peer (P2P) communication model such as decentralization, scalability, fault-tolerance seems to be a natural solution to deal with these challenges. Consequently, the combination of the Semantic Web and the P2P model can be a highly innovative attempt to harness the strengths of both technologies and come up with a scalable infrastructure for RDF data storage and retrieval. In this respect, this survey details the research works that adopt this combination and gives an insight on how to deal with the RDF data at the indexing and querying levels.Le Web Sémantique permet de modéliser, créer et faire des requêtes sur les ressources disponibles sur le Web. Afin de permettre à ses technologies d'exploiter leurs potentiels à l'échelle de l'Internet, il est nécessaire qu'elles reposent sur des infrastructures qui puissent passer à l'échelle ainsi que de répondre aux exigences d'expressivité des types de requêtes qu'elles offrent. Les bonnes propriétés qu'offrent les dernières générations de systèmes pair-à- pair en termes de décentralisation, de tolérance aux pannes ainsi que de passage à l'échelle en font d'eux des candidats prometteurs. La combinaison du modèle pair-à-pair et des technologies du Web Sémantique est une tentative innovante ayant pour but de fournir une infrastructure capable de passer à l'échelle et pouvant stocker et rechercher des données de type RDF. Dans ce contexte, ce rapport présente un état de l'art et discute en détail des travaux autour de systèmes pair-à-pair qui traitent des données de type RDF à large échelle. Nous détaillons leurs mécanismes d'indexation de données ainsi que le traitement des divers types de requêtes offerts

Combining Grid and Cloud Resources by Use of Middleware for SPMD Application

International audienceDistributed computing environments have evolved from in-house clusters to Grids and now Cloud platforms. We, as others, provide HPC benchmarks results over Amazon EC2 that show a lower performance of Cloud resources compared to private resources. So, it is not yet clear how much of impact Clouds will have in high performance computing (HPC). But hybrid Grid/Cloud computing may offer opportunities to increase overall applications performance, while benefiting from in-house computational resources extending them by Cloud ones only whenever needed. In this paper, we advocate the usage of ProActive, a well established middleware in the grid community, for mixed Grid/Cloud computing, extended with features to address Grid/Cloud issues with little or no effort for application developers. We also introduce a framework, developed in the context of the DiscoGrid project, based upon the ProActive middleware to couple HPC domain-decomposition SPMD applications in heterogeneous multi-domain environments. Performance results coupling Grid and Cloud resources for the execution of such kind of highly communicating and processing intensive applications have shown an overhead of about 15%, which is a non-negligible value, but lower enough to consider using such environments to achieve a better cost-performance trade-off than using exclusively Cloud resources

Is there a role for cervicography in the detection of premalignant lesions of the cervix uteri?

The characteristics of cervicography and the Papanicolaou smear test have been compared for the detection of cervix lesions classified as CIN I or more. A total of 4,015 women were entered into the study. The sensitivity of cervicography is significantly higher (McNemar test, P < 0.0001), but its specificity remains significantly lower (McNemar test, P < 0.0001), and its higher sensitivity does not apply to lesions classified as CIN II or more (high-grade lesions). Hence, if patients with a positive screen result are to be referred for colposcopy-biopsy, cervicography is not a suitable alternative to the smear test for the screening of cervical cancer. However, cervicography can be envisaged as a complementary tool to the smear test because of (a) its higher capability to detect high-grade lesions among women less than 35 years old and (b) its potential superiority in following low-grade lesions. It may also serve as a tool for quality assurance audit of the smear test

Programming, Composing, Deploying for the Grid

Grids raise new challenges in the following way: heterogeneity of underlying machines/networks and runtime environments (types and performance characteristics), not a single administrative domain, versatility. So the need to have appropriate programming and runtime solutions in order to write, deploy then execute applications on such heterogeneous distributed hardware in an effective and efficient manner. We propose in this article a solution to those challenges which takes the form of a programming and deployment framework featuring parallel, mobile, secure and distributed objects and components

Inducible expression of beta defensins by human respiratory epithelial cells exposed to Aspergillus fumigatus organisms

<p>Abstract</p> <p>Background</p> <p><it>Aspergillus fumigatus</it>, a saprophytic mould, is responsible for life-threatening, invasive pulmonary diseases in immunocompromised hosts. The role of the airway epithelium involves a complex interaction with the inhaled pathogen. Antimicrobial peptides with direct antifungal and chemotactic activities may boost antifungal immune response.</p> <p>Results</p> <p>The inducible expression of defensins by human bronchial epithelial 16HBE cells and A549 pneumocyte cells exposed to <it>A. fumigatus </it>was investigated. Using RT-PCR and real time PCR, we showed an activation of hBD2 and hBD9 defensin genes: the expression was higher in cells exposed to swollen conidia (SC), compared to resting conidia (RC) or hyphal fragments (HF). The kinetics of defensin expression was different for each one, evoking a putative distinct function for each investigated defensin. The decrease of defensin expression in the presence of heat-inactivated serum indicated a possible link between defensins and the proteins of the host complement system. The presence of defensin peptide hBD2 was revealed using immunofluorescence that showed a punctual cytoplasmic and perinuclear staining. Quantification of the cells stained with anti hBD2 antibody demonstrated that SC induced a greater number of cells that synthesized hBD2, compared to RC or HF. Labelling of the cells with anti-hBD-2 antibody showed a positive immunofluorescence signal around RC or SC in contrast to HF. This suggests co-localisation of hBD2 and digested conidia. The HBD2 level was highest in the supernatants of cells exposed to SC, as was determined by sandwich ELISA. Experiments using neutralising anti-interleukine-1β antibody reflect the autocrine mechanism of defensin expression induced by SC. Investigation of defensin expression at transcriptional and post-transcriptional levels demonstrated the requirement of transcription as well as new protein synthesis during <it>A. fumigatus </it>defensin induction. Finally, induced defensin expression in primary culture of human respiratory cells exposed to <it>A. fumigatus </it>points to the biological significance of described phenomena.</p> <p>Conclusion</p> <p>Our findings provide evidence that respiratory epithelium might play an important role in the immune response during <it>Aspergillus </it>infection. Understanding the mechanisms of regulation of defensin expression may thus lead to new approaches that could enhance expression of antimicrobial peptides for potential therapeutic use during aspergillosis treatment.</p