8,330 research outputs found
Towards trustworthy self-optimization for distributed systems
Abstract. The increasing complexity of computer-based technical systems requires new ways to control them. The initiatives Organic Computing and Autonomic Computing address exactly this issue. They demand future computer systems to adapt dynamically and autonomously to their environment and postulate so-called self-* properties. These are typically based on decentralized autonomous cooperation of the system's entities. Trust can be used as a means to enhance cooperation schemes taking into account trust facets such as reliability. The contributions of this paper are algorithms to manage and query trust information. It is shown how such information can be used to improve self-* algorithms. To quantify our approach evaluations have been conducted
Recommended from our members
Personal mobile grids with a honeybee inspired resource scheduler
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The overall aim of the thesis has been to introduce Personal Mobile Grids (PMGrids)
as a novel paradigm in grid computing that scales grid infrastructures to mobile devices and extends grid entities to individual personal users. In this thesis, architectural designs as well as simulation models for PM-Grids are developed.
The core of any grid system is its resource scheduler. However, virtually all current conventional grid schedulers do not address the non-clairvoyant scheduling problem, where job information is not available before the end of execution. Therefore, this thesis proposes a honeybee inspired resource scheduling heuristic for PM-Grids (HoPe) incorporating a radical approach to grid resource scheduling to tackle this problem. A detailed design and implementation of HoPe with a decentralised self-management and adaptive policy are initiated.
Among the other main contributions are a comprehensive taxonomy of grid systems as well as a detailed analysis of the honeybee colony and its nectar acquisition process (NAP), from the resource scheduling perspective, which have not been presented in any previous work, to the best of our knowledge.
PM-Grid designs and HoPe implementation were evaluated thoroughly through a strictly controlled empirical evaluation framework with a well-established heuristic in high throughput computing, the opportunistic scheduling heuristic (OSH), as a benchmark algorithm. Comparisons with optimal values and worst bounds are conducted to gain a clear insight into HoPe behaviour, in terms of stability, throughput, turnaround time and speedup, under different running conditions of number of jobs and grid scales.
Experimental results demonstrate the superiority of HoPe performance where it
has successfully maintained optimum stability and throughput in more than 95%
of the experiments, with HoPe achieving three times better than the OSH under
extremely heavy loads. Regarding the turnaround time and speedup, HoPe has
effectively achieved less than 50% of the turnaround time incurred by the OSH, while doubling its speedup in more than 60% of the experiments.
These results indicate the potential of both PM-Grids and HoPe in realising futuristic grid visions. Therefore considering the deployment of PM-Grids in real life scenarios and the utilisation of HoPe in other parallel processing and high throughput computing systems are recommended
Towards adaptive multi-robot systems: self-organization and self-adaptation
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The development of complex systems ensembles that operate in uncertain environments is a major challenge. The reason for this is that system designers are not able to fully specify the system during specification and development and before it is being deployed. Natural swarm systems enjoy similar characteristics, yet, being self-adaptive and being able to self-organize, these systems show beneficial emergent behaviour. Similar concepts can be extremely helpful for artificial systems, especially when it comes to multi-robot scenarios, which require such solution in order to be applicable to highly uncertain real world application. In this article, we present a comprehensive overview over state-of-the-art solutions in emergent systems, self-organization, self-adaptation, and robotics. We discuss these approaches in the light of a framework for multi-robot systems and identify similarities, differences missing links and open gaps that have to be addressed in order to make this framework possible
Calculating and Aggregating Direct Trust and Reputation in Organic Computing Systems
The growing complexity of current computer systems requires a high amount of administration, which poses an increasingly challenging task for manual administration. The Autonomic and Organic Computing Initiatives have introduced so called self-x properties, including self-configuration, self-optimization, self-healing, and self-protection, to allow administration to become autonomous. Although research in this area revealed promising results, it expects all participants to further the system goal, i.e., their benevolence is assumed. In open systems, where arbitrary participants can join the systems, this benevolence assumption must be dropped, since such a participant may act maliciously and try to exploit the system. This introduces a not yet considered uncertainty, which needs to be addressed.
In human society, trust relations are used to lower the uncertainty of transactions with unknown interaction partners. Trust is based on past experiences with someone, as well as recommendations of trusted third parties. In this work trust metrics for direct trust, reputation, confidence, and an aggregation of them are presented. While the presented metrics were primarily designed to improve the self-x properties of OC systems they can also be used by applications in Multi-Agent-Systems to evaluate the behavior of other agents. Direct trust is calculated by the Delayed-Ack metric, that assesses the reliability of nodes in Organic Computing systems. The other metrics are general enough to be used with all kinds of contexts and facets to cover any kind of trust requirements of a system, as long as corresponding direct trust values exist. These metrics include reputation (Neighbor-Trust), confidence, and an aggregation of them.
Evaluations based on an Automated Design Space Exploration are conducted to find the best configurations for each metric, especially to identify the importance of direct trust, reputation, and confidence for the total trust value. They illustrate, that reputation, i.e., the recommendations of others, is an important aspect to evaluate the trustworthiness of an interaction partner. In addition, it is shown that a gradual change of priority from reputation to direct trust is preferable instead of a sudden switch when enough confidence in the correctness of ones own experiences is accumulated. All evaluations focus on systems with volatile behavior, i.e., system participants change their behavior over time. In such a system, the ability to adapt fast to behavior changes has turned out to be the most important parameter.Die steigende Komplexität aktueller Systeme benötigt einen hohen Grad an Administration, was eine wachsende Herausforderung für die manuelle Administration darstellt. Die Autonomic- und Organic-Computing Initiativen haben so genannte Selbst-x Eigenschaften vorgestellt, unter anderem Selbst-Konfiguration, Selbst-Optimierung, Selbst-Heilung sowie Selbst-Schutz, die eine autonome Administration erlauben. Obwohl die Forschung in diesem Gebiet erfolgversprechende Ergebnisse geliefert hat, wird von allen Teilnehmern erwartet, dass sie das Systemziel vorantreiben, d.h., ihr Wohlwollen wird vorausgesetzt. In offenen Systemen, in denen beliebige Teilnehmer dem System beitreten können, muss diese Wohlverhaltensannahme fallen gelassen werden, da solche Teilnehmer bösartig handeln und versuchen können, das System auszunutzen.
In einer menschlichen Gesellschaft werden Vertrauensbeziehungen dazu benutzt, die Unsicherheit von Transaktionen mit unbekannten Interaktionspartnern zu mindern. Vertrauen basiert auf den bisherigen Erfahrungen mit Jemandem und auf Empfehlungen von Dritten. In dieser Arbeit werden Trust-Metriken für direkten Trust, Reputation, Konfidenz und deren Aggregation vorgestellt. Obwohl die vorgestellten Metriken hauptsächlich dafür entworfen wurden, die Selbst-x Eigenschaften von Organic-Computing Systemen zu verbessern, können sie ebenso von Applikationen in Multi-Agenten-Systemen benutzt werden, um das Verhalten anderer Agenten einschätzen zu können. Direkter Trust wird durch die Delayed-Ack Metrik berechnet, welche die Zuverlässigkeit von Knoten in Organic-Computing Systemen einschätzt. Die anderen Metriken sind allgemein genug gehalten, um in jedem Kontext und jeder Facette benutzt werden zu können, in dem ein System operiert, solange ein Trust-Wert für direkten Trust existiert. Diese Metriken beinhalten Reputation (Neighbor-Trust), Konfidenz und die Aggregation dieser.
Es werden Evaluationen basierend auf einer automatischen Design Space Exploration durchgeführt, um die beste Konfiguration für jede Metrik zu finden, um dabei speziell die Wichtigkeit von direktem Trust, Reputation und Konfidenz auf den gesamten Trust-Wert zu identifizieren. Sie veranschaulichen, dass Reputation, d.h. die Vorschläge Dritter, ein wichtiger Aspekt ist, um die Vertrauenswürdigkeit eines Interaktionspartners einschätzen zu können. Zusätzlich zeigen sie, dass ein gradueller Wechsel von Reputation zu eigenen Erfahrungen einem plötzlichen Wechsel vorzuziehen ist, wenn genug Zuversicht auf die Korrektheit der eigenen Erfahrungen vorhanden ist. Alle Auswertungen befassen sich mit Systemen mit unbeständigem Verhalten, d.h. Systemteilnehmer ändern ihr Verhalten über die Zeit. In solch einem System hat sich herausgestellt, dass die Fähigkeit, sich schnell an Verhaltensänderungen anpassen zu können, der wichtigste Faktor ist
State-of-the-art in aerodynamic shape optimisation methods
Aerodynamic optimisation has become an indispensable component for any aerodynamic design over the past 60 years, with applications to aircraft, cars, trains, bridges, wind turbines, internal pipe flows, and cavities, among others, and is thus relevant in many facets of technology. With advancements in computational power, automated design optimisation procedures have become more competent, however, there is an ambiguity and bias throughout the literature with regards to relative performance of optimisation architectures and employed algorithms. This paper provides a well-balanced critical review of the dominant optimisation approaches that have been integrated with aerodynamic theory for the purpose of shape optimisation. A total of 229 papers, published in more than 120 journals and conference proceedings, have been classified into 6 different optimisation algorithm approaches. The material cited includes some of the most well-established authors and publications in the field of aerodynamic optimisation. This paper aims to eliminate bias toward certain algorithms by analysing the limitations, drawbacks, and the benefits of the most utilised optimisation approaches. This review provides comprehensive but straightforward insight for non-specialists and reference detailing the current state for specialist practitioners
- …