3,675 research outputs found
Tree structure data change detection method
The new method, increasing efficiency and reliability of change detection in three structures in the Internet data under indetermination of data structure (DTD, XML-Schema) is proposed in this paper. The Boolean linear programming problem was
solved in two exact methods – modified Balazs with filter and modified DP method and A modified method for selecting a
neural network architecture was proposed. There is also considered publish/subscribe system description enhanced with core module, which provides notifications of changes to subscribers only in case they occurred
Cordies:Expressive event correlation in distributed systems
Complex Event Processing (CEP) is the method of choice for the observation of system states and situations by means of events. A number of systems have been introduced that provide CEP in selected environments. Some are restricted to centralised systems, or to systems with synchronous communication, or to a limited space of event relations that are defined in advance. Many modern systems, though, are inherently distributed and asynchronous, and require a more powerful CEP. We present Cordies, a distributed system for the detection of correlated events that is designed for the operation in large-scale, heterogeneous networks and adapts dynamically to changing network conditions. With its expressive language to describe event relations, it is suitable for environments where neither the event space nor the situations of interest are predefined but are constantly adapted. In addition, Cordies supports Quality-of-Service (QoS) for communication in distributed event correlation detection
Discreet - Pub/Sub for Edge Systems
The number of devices connected to the Internet has been growing exponentially over
the last few years. Today, the amount of information available to users has reached a
point that makes it impossible to consume it all, showing that we need better ways to
filter what kind of information is sent our way. At the same time, while users are online
and access all this information, their actions are also being collected, scrutinized and
commercialized with little regard for privacy.
This thesis addresses those issues in the context of a decentralized Publish/Subscribe
solution for edge systems. Working at the edge of the Internet aims to prevent centralized
control from a single entity and lessen the chance of abuse. Our goal was to devise a
solution that achieves efficient message delivery, with good load-balancing properties,
without revealing its participants subscription interests to preserve user privacy.
Our solution uses cryptography and probabilistic data sets as a way to obfuscate event
topics and user subscriptions. We modeled a cooperative solution, where publisher and
subscriber nodes work in concert to route events among themselves, by leveraging a onehop
structured overlay. By using an experimental evaluation, we attest the scalability and
general performance of the proposed algorithms, including latency, false negative and
false positive rates, and other useful metrics.O número de aparelhos ligados a Internet têm vindo a crescer exponencialmente ao
longo dos últimos anos. Hoje em dia, a quantidade de informação que os utilizadores
têm disponível, chegou a um ponto que torna impossível o seu total consumo. Isto leva
a que seja necessário encontrarmos melhores formas de filtrar a informação que recebemos.
Ao mesmo tempo, as ações do utilizadores estão a ser recolhidas, examinadas e
comercializadas, sem qualquer respeito pela privacidade.
Esta tese trata destes assuntos no contexto de um sistema Publish/Subscribe descentralizado,
para sistemas na periferia. O objectivo de operar na preferia da Internet está
em prevenir o controlo centralizado por uma única entidade e diminuir a oportunidade
para abusos. O nosso objectivo foi conceber uma solução que realiza entrega de mensagens
eficientemente, com boas propriedades na distribuição de carga e sem revelar on
interesses dos participantes, de forma a preservar a sua privacidade.
A nossa solução usa criptografia e estruturas de dados probabilísticas, como uma
forma de ofuscar os tópicos dos eventos e as subscrições dos utilizadores. Modelamos
o sistema com o objectivo de ser uma solução cooperativa, onde ambos os tipos de nós
Editores e Assinantes trabalham em concertadamente para encaminhar eventos entre
eles, ao fazerem uso de uma estrutura de rede sobreposta com um salto. Fazendo uma
avaliação experimental testámos a escalabilidade e o desempenho geral dos algoritmos
propostos, incluindo a latência, falsos negativos, falsos positivos e outras métricas úteis
Conflict-Free Replicated Data Types in Dynamic Environments
Over the years, mobile devices have become increasingly popular and gained improved
computation capabilities allowing them to perform more complex tasks such as
collaborative applications. Given the weak characteristic properties of mobile networks,
which represent highly dynamic environments where users may experience regular involuntary
disconnection periods, the big question arises of how to maintain data consistency.
This issue is most pronounced in collaborative environments where multiple users interact
with each other, sharing a replicated state that may diverge due to concurrency
conflicts and loss of updates.
To maintain consistency, one of today’s best solutions is Conflict-Free Replicated Data
Types (CRDTs), which ensure low latency values and automatic conflict resolution, guaranteeing
eventual consistency of the shared data. However, a limitation often found on
CRDTs and the systems that employ them is the need for the knowledge of the replicas
whom the state changes must be disseminated to. This constitutes a problem since it is
inconceivable to maintain said knowledge in an environment where clients may leave
and join at any given time and consequently get disconnected due to mobile network
communications unreliability.
In this thesis, we present the study and extension of the CRDT concept to dynamic
environments by introducing the developed P/S-CRDTs model, where CRDTs are coupled
with the publisher/subscriber interaction scheme and additional mechanisms to
ensure users are able to cooperate and maintain consistency whilst accounting for the
consequent volatile behaviors of mobile networks. The experimental results show that
in volatile scenarios of disconnection, mobile users in collaborative activity maintain
consistency among themselves and when compared to other available CRDT models, the
P/S-CRDTs model is able to decouple the required knowledge of whom the updates must
be disseminated to, while ensuring appropriate network traffic values
A Tour of MOOS-IvP Autonomy Software Modules
This paper provides an overview of the MOOS-IvP autonomy software modules. The MOOS-IvP collection of software, i.e., codebase, described here has been developed and is currently maintained by three organizations - Oxford University, Massachusetts Institute of Technology (MIT), and the Naval Undersea Warfare Center (NUWC) Division Newport Rhode Island. The objective of this paper is to provide a comprehensive list of modules and provide for each (a) a general description of functionality, (b) dependency relationships to other modules, (c) rough order of magnitude in complexity or size, (d) authorship, and (e) current and planned distribution access
Cross-layer Peer-to-Peer Computing in Mobile Ad Hoc Networks
The future information society is expected to rely heavily on wireless technology. Mobile access to the Internet is steadily gaining ground, and could easily end up exceeding the number of connections from the fixed infrastructure. Picking just one example, ad hoc networking is a new paradigm of wireless communication for mobile devices. Initially, ad hoc networking targeted at military applications as well as stretching the access to the Internet beyond one wireless hop. As a matter of fact, it is now expected to be employed in a variety of civilian applications. For this reason, the issue of how to make these systems working efficiently keeps the ad hoc research community active on topics ranging from wireless technologies to networking and application systems.
In contrast to traditional wire-line and wireless networks, ad hoc networks are expected to operate in an environment in which some or all the nodes are mobile, and might suddenly disappear from, or show up in, the network. The lack of any centralized point, leads to the necessity of distributing application services and responsibilities to all available nodes in the network, making the task of developing and deploying application a hard task, and highlighting the necessity of suitable middleware platforms.
This thesis studies the properties and performance of peer-to-peer overlay management algorithms, employing them as communication layers in data sharing oriented middleware platforms. The work primarily develops from the observation that efficient overlays have to be aware of the physical network topology, in order to reduce (or avoid) negative impacts of application layer traffic on the network functioning. We argue that cross-layer cooperation between overlay management algorithms and the underlying layer-3 status and protocols, represents a viable alternative to engineer effective decentralized communication layers, or eventually re-engineer existing ones to foster the interconnection of ad hoc networks with Internet infrastructures. The presented approach is twofold. Firstly, we present an innovative network stack component that supports, at an OS level, the realization of cross-layer protocol interactions. Secondly, we exploit cross-layering to optimize overlay management algorithms in unstructured, structured, and publish/subscribe platforms
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