We address the issue of measuring storage, or query load distribution fairness in peer-to-peer data management systems. Existing metrics may look promising from the point of view of specific peers, while in reality be...
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ISBN:
(纸本)1424408024
We address the issue of measuring storage, or query load distribution fairness in peer-to-peer data management systems. Existing metrics may look promising from the point of view of specific peers, while in reality being far from optimal from a global perspective. Thus, first we define the requirements and study the appropriateness of various statistical metrics for measuring load distribution fairness towards these requirements. The metric proposed as most appropriate is the Gini coefficient (G). Second, we develop novel distributed sampling algorithms to compute G on-line, with high precision, efficiently, and scalably. Third, we show how G can readily be utilized on-line by higher-level algorithms which can now know when to best intervene to correct load imbalances. Our analysis and experiments testify for the efficiency and accuracy of these algorithms, permitting the online use of a rich and reliable metric, conveying a global perspective of the distribution.
The problem of trajectory similarity in moving object databases is a relatively new topic in the spatial and spatiotemporal database literature. Existing work focuses on the spatial notion of similarity ignoring the t...
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ISBN:
(纸本)1424408024
The problem of trajectory similarity in moving object databases is a relatively new topic in the spatial and spatiotemporal database literature. Existing work focuses on the spatial notion of similarity ignoring the temporal dimension of trajectories and disregarding the presence of a general-purpose spatiotemporal index. In this work, we address the issue of spatiotemporal trajectory similarity search by defining a similarity metric, proposing an efficient approximation method to reduce its calculation cost, and developing novel metrics and heuristics to support k-most-similar-trajectory search in spatiotemporal databases exploiting on existing R-tree-like structures that are already found there to support more traditional queries. Our experimental study, based on real and synthetic datasets, verifies that the proposed similarity metric efficiently retrieves spatiotemporally similar trajectories in cases where related work fails, while at the same time the proposed algorithm is shown to be efficient and highly scalable.
The content-based publish/subscribe (pub/sub) paradigm for system design is becoming increasingly popular, offering unique benefits for a large number of data-intensive applications. Coupled with the peer-to-peer tech...
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ISBN:
(纸本)1424408024
The content-based publish/subscribe (pub/sub) paradigm for system design is becoming increasingly popular, offering unique benefits for a large number of data-intensive applications. Coupled with the peer-to-peer technology, it can serve as a central building block for such applications deployed over a large-scale network infrastructure. A key problem toward the creation of large-scale content-based pub/sub infrastructures relates to dealing efficiently with continuous queries (subscriptions) with rich predicates on string attributes; in this work we study the problem of efficiently and accurately matching substring queries to incoming events.
Dense clinical data like 3D Computed Tomography (CT) scans can be visualized together with real-time imaging for a number of medical intervention applications. However, it is difficult to provide a fused visualization...
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It is well known that both space and the spatial organization play an important role in our work and learning environments as well as in everyday life. There is a definite need for many persons to design their space a...
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It is well known that both space and the spatial organization play an important role in our work and learning environments as well as in everyday life. There is a definite need for many persons to design their space along with an expert and to preview it in order to test its functionality. Many times there is a need for the inhabitants and workers to collaborate in order to co-design their space from distance. Multi-user 3D virtual environments are a powerful form of collaborative telecommunication applications, enabling the users to share a common three dimensional space and interact with each other as well as with the environment surrounding them, in order to collaboratively solve problems or aid learning processes. This paper presents the work done for extending a multi-user virtual environments platform, to support collaborative spatial design applications. Furthermore, a usage scenario is presented concerning the collaborative design of a classroom for educational purposes.
Wireless sensor networks are comprised of a vast number of ultra-small autonomous computing, communication and sensing devices, with restricted energy and computing capabilities, that co-operate to accomplish a large ...
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In this work we study the combination of multicost routing and variable transmission power in wireless ad-hoc networks. In multicost routing, each link is assigned a cost vector consisting of several parameters. These...
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In this work we study the combination of multicost routing and variable transmission power in wireless ad-hoc networks. In multicost routing, each link is assigned a cost vector consisting of several parameters. These parameters are treated separately and are combined at the end of the algorithm using various optimization functions, corresponding to different routing schemes, for selecting the optimal path. The cost parameters we use are the hop count, the interference caused, the node residual energies, and the node transmission powers. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multicost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.
It is more convenient to talk about changes in a domainspecific way than to formulate them at the programming construct level or-even worse-purely lexical level. Using aspect-oriented programming, changes can be modul...
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It is more convenient to talk about changes in a domainspecific way than to formulate them at the programming construct level or-even worse-purely lexical level. Using aspect-oriented programming, changes can be modularized and made reapplicable. In this paper, selected change types in web applications are analyzed. They are expressed in terms of general change types which, in turn, are implemented using aspect-oriented programming. Some of general change types match aspect-oriented design patterns or their combinations.
Data propagation in wireless sensor networks is usually performed as a multihop process. To deliver a single message, the resources of many sensor nodes are used and a lot of energy is spent. Recently, a novel approac...
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Data propagation in wireless sensor networks is usually performed as a multihop process. To deliver a single message, the resources of many sensor nodes are used and a lot of energy is spent. Recently, a novel approach is catching momentum because of important applications; that of having a mobile sink move inside the network area and collects the data with low energy cost. Here we extend this line of research by proposing and evaluating three new protocols. Our protocols are novel in a) investigating the impact of having many mobile sinks; b) in weak models with restricted mobility, proposing and evaluating a mix of static and mobile sinks; and c) proposing a distributed protocol that tends to equally spread the sinks in the network to further improve performance. Our protocols are simple, based on randomization and assume locally obtainable information. We perform an extensive evaluation via simulation; our findings demonstrate that our solutions scale very well with respect to the number of sinks and significantly reduce energy consumption and delivery delay
In this paper, we study the burstification effect on the TCP synchronization and TCP congestion window mechanism. It is shown that short assembly times are optimal for flows with similar characteristics, while large a...
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ISBN:
(纸本)9781424414321
In this paper, we study the burstification effect on the TCP synchronization and TCP congestion window mechanism. It is shown that short assembly times are optimal for flows with similar characteristics, while large assembly time provide a higher notion of fairness. In addition, this paper analyzes the synchronization of multiple TCP flows when aggregated together over the same optical bursts. It is shown that there is a strong TCP synchronization effect upon burst losses, in the sense that flows’ windows increase/decrease simultaneously, resulting to a significant variation of outgoing traffic. These deficiencies may be dealt with employing a multi-queue burst assembly scheme with different timers and taking into account the TCP dynamics.
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