A comparison using APPL and PVM for a parallel implementation of an unstructured grid generation program

Efforts to parallelize the VGRIDSG unstructured surface grid generation program are described. The inherent parallel nature of the grid generation algorithm used in VGRIDSG was exploited on a cluster of Silicon Graphics IRIS 4D workstations using the message passing libraries Application Portable Parallel Library (APPL) and Parallel Virtual Machine (PVM). Comparisons of speed up are presented for generating the surface grid of a unit cube and a Mach 3.0 High Speed Civil Transport. It was concluded that for this application, both APPL and PVM give approximately the same performance, however, APPL is easier to use

Robust Query Optimization Methods With Respect to Estimation Errors: A Survey

International audienceThe quality of a query execution plan chosen by a Cost-Based Optimizer (CBO) depends greatly on the estimation accuracy of input parameter values. Many research results have been produced on improving the estimation accuracy, but they do not work for every situation. Therefore, "robust query optimization" was introduced, in an effort to minimize the sub-optimality risk by accepting the fact that estimates could be inaccurate. In this survey, we aim to provide an overview of robust query optimization methods by classifying them into different categories, explaining the essential ideas, listing their advantages and limitations, and comparing them with multiple criteria

Commentary on "can state and local governments rely on alternative tax sources?"

State finance ; Local finance

Argumentation systems and belief functions

Uncertain knowledge can be represented in the framework of argumentation systems. In this framework, uncertainty is expressed using so-called assumptions. Depending on the setting of the assumptions, a given hypothesis of interest can be proved or falsified. The main goal of assumption-based reasoning is to determine the set of all supporting arguments for a given hypothesis. Such a supporting argument is a particular setting of assumptions. The assignment of probabilities to assumptions leads to the framework of probabilistic argumentation systems and allows an additional quantitative judgement of a given hypothesis. One possibility to compute the degree of support for a given hypothesis is to compute first the corresponding set of supporting arguments and then to derive the desired result. The problem of this approach is that the set of supporting arguments is sometimes very huge and can't be represented explicitly. This thesis proposes an alternative way for computing degrees of support which is often superior to the first approach. Instead of computing a symbolic result from which the numerical result is derived, we avoid symbolic computations right away. This can be done due to the fact that degree of support corresponds to the notion of normalized belief in Dempster-Shafer theory. We will show how a probabilistic argumentation system can be transformed into a set of independent mass functions. For efficient computations, the local computation framework of Shenoy is used. In this framework, computation is based on a message-passing scheme in a join tree. Four different architectures could be used for propagating potentials in the join tree. These architectures correspond to a complete compilation of the knowledge which allows to answer queries fast. In contrast, this thesis proposes a new method which corresponds to a partial compilation of the knowledge. This method is particularly interesting if there are only a few queries. In addition, it can prevent that the join tree has to be reconstructed in order to answer a given query. Finally, the language ABEL is presented. It allows to express probabilistic argumentations systems in a convenient way. We will show how several examples from different domains can be modeled using ABEL. These examples are also used to point out important aspects of the computational theory presented in the first chapters of this thesis.Das Konzept der Argumentations-Systeme dient dem Zweck der Darstellung von insicherer oder unpräziser Information. Unsicherheit wird in Argumentations- Systemen durch sogenannte Annahmen dargestellt. Eine gegebene Hypothese kann dann in Abhängigkeit der Annahmen bewiesen oder verworfen werden. Hauptaufgabe des Annahmen-basierten Schliessens ist die Bestimmung von Argumenten welche eine gegebene Hypothese stützen. Die Zuordnung von Wahrscheinlichkeiten zu den Annahmen führt zum Konzept der probabilistischen Argumentations-Systeme. Eine zusätzliche quantitative Beurteilung einer gegebenen Hypothese wird dadurch möglich. Ein erster Ansatz den Grad der Unterstützung einer Hypothese zu berechnen besteht darin, zuerst die Menge aller stützenden Argumente zu berechnen Das gewünschte numerische Resultat kann dann daraus abgeleitet werden. Häufig ist dieser Ansatz jedoch nicht durchführbar weil die Menge der unterstützenden Argumente zu gross und deshalb nicht explizit darstellbar ist. In dieser Arbeit stellen wir einen alternativen Ansatz zur Berechnung des Grades der Unterstützung einer Hypothese vor. Dieser alternative Ansatz ist oft effizienter als der erste Ansatz. Anstatt ein symbolisches Zwischenresultats zu berechnen von welchem dann das numerische Endresultat abgeleitet wird, vermeiden wir symbolisches Rechnen schon ganz zu Beginn. Dies ist möglich weil der Grad der Unterstützung zum Begriff der Glaubwürdigkeit in der Dempster-Shafer Theorie äquivalent ist. Wir werden zeigen wie ein gegebenes probabilistisches Argumentations-System in eine Menge von equivalenten Mass Funktionen überführt werden kann. Als Grundlage für die Berechnungen wird das Konzept der Valuations Netzwerke verwendet. Dadurch wird versucht, die Berechnungen möglichst effizient durchzuführen. Es gibt dabei vier verschiedene Rechenarchitekturen. Diese vier Rechenarchitekturen entsprechen einer vollständigen Kompilation der vorhandenen Informationen. Der Vorteil davon ist, dass Abfragen dann sehr schnell beantwortet werden können. Im Gegensatz dazu stellen wir in dieser Arbeit eine neue Methode vor die eher einer partiellen Kompiliation der vorhandenen Informationen entspricht. Diese neue Methode ist vorallem interessant, falls nur wenige Abfragen zu beantworten sind. Des weitern kann diese Methode verhindern, dass ein Valuationsnetz zur Beantwortung einer Abfrage neu konstruiert werden muss. Zum Schluss geben wir eine Einführung in die Modellierspreche ABEL. Diese Sprache erlaubt, probabilistische Argumentations-Systeme auf eine geeignete und komfortable Art und Weise zu formulieren. Wir zeigen wie Beispiele aus verschiedenen Anwendungsgebieten mit ABEL modelliert werden können. Diese Beispiele werden auch dazu verwendet, wichtige Aspekte der in den ersten Kapiteln dieser Arbeit dargestellten Rechentheorie zu unterstreichen

Engineering Agile Big-Data Systems

To be effective, data-intensive systems require extensive ongoing customisation to reflect changing user requirements, organisational policies, and the structure and interpretation of the data they hold. Manual customisation is expensive, time-consuming, and error-prone. In large complex systems, the value of the data can be such that exhaustive testing is necessary before any new feature can be added to the existing design. In most cases, the precise details of requirements, policies and data will change during the lifetime of the system, forcing a choice between expensive modification and continued operation with an inefficient design.Engineering Agile Big-Data Systems outlines an approach to dealing with these problems in software and data engineering, describing a methodology for aligning these processes throughout product lifecycles. It discusses tools which can be used to achieve these goals, and, in a number of case studies, shows how the tools and methodology have been used to improve a variety of academic and business systems

Active yellow pages: a pipelined resource management architecture for wide-area network computing

This paper describes a novel, pipelined resource management architecture for computational grids. The design is based on two key realizations. One is that resource management involves a sequence of tasks that is best handled by a pipeline. As shown in the paper, this approach results, in a scalable architecture for decentralized scheduling. The other realization is that static aggregation of resources for improved scheduling is inadequate in wide-area computing environments because the needs of users and jobs change with both, location and time. The described architecture addresses this problem by dynamically aggregating resources in a manner that continuously optimizes system response. This is accomplished by way of an active yellow pages directory that allows aggregation constraints to be (re)defined on the fly. An initial prototype of the active yellow pages service has been deployed in the PUNCH network computing environment. Experiences with the production PUNCH system and preliminary results from controlled experiments indicate that the active yellow pages service performs well.Peer Reviewe

Survey on Quality of Observation within Sensor Web Systems

The Sensor Web vision refers to the addition of a middleware layer between sensors and applications. To bridge the gap between these two layers, Sensor Web systems must deal with heterogeneous sources, which produce heterogeneous observations of disparate quality. Managing such diversity at the application level can be complex and requires high levels of expertise from application developers. Moreover, as an information-centric system, any Sensor Web should provide support for Quality of Observation (QoO) requirements. In practice, however, only few Sensor Webs provide satisfying QoO support and are able to deliver high-quality observations to end consumers in a specific manner. This survey aims to study why and how observation quality should be addressed in Sensor Webs. It proposes three original contributions. First, it provides important insights into quality dimensions and proposes to use the QoO notion to deal with information quality within Sensor Webs. Second, it proposes a QoO-oriented review of 29 Sensor Web solutions developed between 2003 and 2016, as well as a custom taxonomy to characterise some of their features from a QoO perspective. Finally, it draws four major requirements required to build future adaptive and QoO-aware Sensor Web solutions