185,208 research outputs found
Moreau.
No full textMOREAU.
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Scalability and Robustness of a Network Resource Allocation System Using Market-Based Agents
No full textIn this paper, we consider issues associated with scalability and robustness in designing a market-based multi-agent system that allocates bandwidth in a communications network. Specifically, an empirical evaluation is carried out to assess the system performance under a variety of design configurations in order to provide an insight into network deployment issues. This extends our previous work in which we developed an application that makes use of market-based software agents that compete in decentralised marketplaces to buy and sell bandwidth resources in a network that is partitioned into regions, each with a separate market server. We investigate the average call success rate and average message load per market server, as the number of markets are scaled up in a fixed size network. The same investigations are performed in the presence of single market failures. Finally, for both the failure and non-failure cases, a trade-off is found between their average call success rates and message load per server in order to find an optimum number of regions to deploy in the network
Scalability and robustness of a market-based network resource allocation system
No full textIn this paper, we consider issues related to scalability and robustness in designing a market-based multi-agent system that allocates bandwidth in a communications network. Specifically, an empirical evaluation is carried out to assess the system performance under a variety of design configurations in order to provide an insight into network deployment issues. This extends our previous work in which we developed an application that makes use of market-based software agents that compete in decentralised marketplaces to buy and sell bandwidth resources. Our new results show that given a light to moderate network traffic load, partitioning the network into a few regions, each with a separate market server, gives a higher call success rate than by using a single market. Moreover, a trade-off in the number of regions was also noted between the average call success rate and the number of messages received per market server. Finally, given the possibility of market failures, we observe that the average call success rates increase with an increasing number of markets until a maximum is reached
Standardisation of Provenance Systems in Service Oriented Architectures --- White Paper
No full textThis White Paper presents provenance in computer systems as a mechanism by which business and e-science can undertake compliance validation and analysis of their past processes. We discuss an open approach that can bring benefits to application owners, IT providers, auditors and reviewers. In order to capitalise on such benefits, we make specific recommendations to move forward a standardisation activity in this domain
The Foundations for Provenance on the Web
No full textProvenance, i.e., the origin or source of something, is becoming an important concern, since it offers the means to verify data products, to infer their quality, to analyse the processes that led to them, and to decide whether they can be trusted. For instance, provenance enables the reproducibility of scientific results; provenance is necessary to track attribution and credit in curated databases; and, it is essential for reasoners to make trust judgements about the information they use over the Semantic Web. As the Web allows information sharing, discovery, aggregation, filtering and flow in an unprecedented manner, it also becomes very difficult to identify, reliably, the original source that produced an information item on the Web. Since the emerging use of provenance in niche applications is undoubtedly demonstrating the benefits of provenance, we contend that provenance can and should reliably be tracked and exploited on the Web, and we survey the necessary foundations to achieve such a vision. Using multiple data sources, we have compiled the largest bibliographical database on provenance so far. This large corpus allows us to analyse emerging trends in the research community. Specifically, using the CiteSpace tool, we identify clusters of papers that constitute research fronts, from which we derive characteristics that we use to structure our foundational framework for provenance on the Web. We note that such an endeavour requires a multi-disciplinary approach, since it requires contributions from many computer science sub-disciplines, but also other non-technical fields given the human challenge that is anticipated. To develop our vision, it is necessary to provide a definition of provenance that applies to the Web context. Our conceptual definition of provenance is expressed in terms of processes, and is shown to generalise various definitions of provenance commonly encountered. Furthermore, by bringing realistic distributed systems assumptions, we refine our definition as a query over assertions made by processes. Given that the majority of work on provenance has been undertaken by the database, workflow and e-science communities, we review some of their work, contrasting approaches, and focusing on important topics we believe to be crucial for bringing provenance to the Web, such as abstraction, collections, storage, queries, workflow evolution, semantics and activities involving human interactions. However, provenance approaches developed in the context of databases and workflows essentially deal with closed systems. By that, we mean that workflow or database management systems are in full control of the data they manage, and track their provenance within their own scope, but not beyond. In the context of the Web, a broader approach is required by which chunks of provenance representation can be brought together to describe the provenance of information flowing across multiple systems. This is the specific purpose of the Open Provenance Vision, which is an approach that consists of controlled vocabulary, serialization formats and interfaces that allow the provenance of individual systems to be expressed, connected in a coherent fashion, and queried seamlessly. In this context, the Open Provenance Model is an emerging community-driven representation of provenance, which has been actively used by some twenty teams to exchange provenance information according to the Open Provenance Vision. Having identified an open approach and a model for provenance, we then look at techniques that have been proposed to expose provenance over the Web. We also study how Semantic Web technologies have been successfully exploited to express, query and reason over provenance. Symmetrically, we also identify how Semantic Web technologies such as RDF underpinning the Linked Data effort bring their own difficulties with respect to provenance. A powerful argument for provenance is that it can help make systems transparent, so that it becomes possible to determine whether a particular use of information is appropriate under a set of rules. Such capability helps make systems and information accountable. To offer accountability, provenance itself must be authentic, and rely on security approaches that we review. We then discuss systems where provenance is the basis of an auditing mechanism to check past processes against rules or regulations. In practice, not all users want to check and audit provenance, instead, they may rely on measures of quality or trust; hence, we review emerging provenance-based approaches to compute trust and quality of data
Birrell's Distributed Reference Listing Revisited
No full textThe Java RMI collector is arguably the most widely used distributed garbage collector. Its distributed reference listing algorithm was introduced by Birrell in the context of Network Objects, where the description was informal and heavily biased toward implementation. In this paper, we formalise this algorithm in an implementation-independent manner, which allows us to clarify weaknesses of the initial presentation. In particular, we discover cases critical to the correctness of the algorithm that are not accounted for by Birrell. We use our formalisation to derive an invariant-based proof of correctness of the algorithm that avoids notoriously difficult temporal reasoning. Furthermore, we offer a novel graphical representation of the state transition diagram, which we use to provide intuitive explanations of the algorithm and to investigate its tolerance to faults in a systematic manner. Finally, we examine how the algorithm may be optimised, either by placing constraints on message channels or by tightening the coupling between application program and distributed garbage collector
Dynamic Discovery of Composable Type Adapters for Practical Web Services Workflow
No full textAs the Web Services and Grid community adopt Semantic Web technology, we observe a shift towards higher-level workflow composition and service discovery practices. While this provides excellent functionality to non-expert users, more sophisticated middleware is required to hide the details of service integration. By investigating a common Bioinformatics use case, we observe the need for Type Adaptor components to be inserted into Workflows to harmonise syntactically incompatible interfaces. In this paper, we propose a generic Type Adaptor description approach that can be used in conjunction with existing service registries to facilitate automatic syntactic mediation. We demonstrate our implementation before evaluating both the translation approach we employ, and the relative cost of using a registry for Type Adaptor discovery
Modelling & simulating chained negotiation to enable sharing of notifications
No full textNotification services (NSs) are middleware components providing asynchronous message delivery between publishers and consumers. Multiple interconnected NSs form a distributed NS, with each NS routing notifications between publishers and consumers at different locations, enabling consumers to share subscriptions, reducing the number of messages sent. Consumers can specify Quality of Service (QoS) levels when subscribing to a NS, using negotiation to find QoS levels acceptable to both parties. However, if consumers specify sufficiently different QoS levels, notifications cannot be shared and new subscriptions must be made. Chained negotiation can be used to negotiate QoS levels through intermediate NSs, enabling the reuse of existing subscriptions for additional consumers. In this paper, we present a chained negotiation engine, evaluating its performance and behaviour, showing that it enables negotiation over QoS while still sharing notifications, and that it provides better results for a consumer by negotiation directly with the publisher
R. Chevallier éd. Présence de Cicéron. Actes du Colloque des 25, 26 septembre 1982. Hommage au R. P. M. Testard
No full textMoreau Philippe. R. Chevallier éd. Présence de Cicéron. Actes du Colloque des 25, 26 septembre 1982. Hommage au R. P. M. Testard. In: Revue belge de philologie et d'histoire, tome 65, fasc. 1, 1987. Antiquité - Oudheid. pp. 163-164
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