Results 1 - 10
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97
Discovering similar multidimensional trajectories
- In ICDE
, 2002
"... We investigate techniques for analysis and retrieval of object trajectories in a two or three dimensional space. Such kind of data usually contain a great amount of noise, that makes all previously used metrics fail. Therefore, here we formalize non-metric similarity functions based on the Longest C ..."
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Cited by 253 (6 self)
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We investigate techniques for analysis and retrieval of object trajectories in a two or three dimensional space. Such kind of data usually contain a great amount of noise, that makes all previously used metrics fail. Therefore, here we formalize non-metric similarity functions based on the Longest Common Subsequence (LCSS), which are very robust to noise and furthermore provide an intuitive notion of similarity between trajectories by giving more weight to the similar portions of the sequences. Stretching of sequences in time is allowed, as well as global translating of the sequences in space. Efficient approximate algorithms that compute these similarity measures are also provided. We compare these new methods to the widely used Euclidean and Time Warping distance functions (for real and synthetic data) and show the superiority of our approach, especially under the strong presence of noise. We prove a weaker version of the triangle inequality and employ it in an indexing structure to answer nearest neighbor queries. Finally, we present experimental results that validate the accuracy and efficiency of our approach. 1
Efficient Concurrency Control for Broadcast Environments
"... A crucial consideration in environments where data is broadcast to clients is the low bandwidth available for clients to communicate with servers. Advanced applications in such environments do need to read data that is mutually consistent aswell as current. However, given the asymmetric communicatio ..."
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Cited by 56 (1 self)
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A crucial consideration in environments where data is broadcast to clients is the low bandwidth available for clients to communicate with servers. Advanced applications in such environments do need to read data that is mutually consistent aswell as current. However, given the asymmetric communication capabilities and the needs of clients in mobile environments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. We thus propose the use of a weaker correctness criterion called update consistency and outline mechanisms based on this criterion that ensure (1) the mutual consistency of data maintained by the server and read by clients, and (2) the currency of data read by clients. Using these mechanisms, clients can obtain data that is current and mutually consistent "off the air", i.e., without contacting the server to, say, obtain locks. Experimental results show a substantial reduction in response times as compared to existing (serializability-based) approaches. A further attractive feature of the approach is that if caching is possible at a client, weaker forms of currency can be obtained while still satisfying the mutual consistency of data.
Data Management in Location-Dependent Information Services
- IEEE Pervasive Computing
, 2002
"... this article, we discuss location -dependent information access in a mobile-pervasive environment, in particular in a cellular mobile system, and present new research issues arising from on-demand access, broadcast, and data caching ..."
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Cited by 40 (10 self)
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this article, we discuss location -dependent information access in a mobile-pervasive environment, in particular in a cellular mobile system, and present new research issues arising from on-demand access, broadcast, and data caching
Generating Semantics-Based Trajectories of Moving Objects
- INTERNATIONAL WORKSHOP ON EMERGING TECHNOLOGIES FOR GEO-BASED APPLICATIONS
, 2000
"... The domain of spatiotemporal applications is a treasure trove of new types of data as well as queries. For designing and testing novel data types and access methods that will support these applications, large spatiotemporal datasets are needed. As in many cases it is not possible to obtain rea ..."
Abstract
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Cited by 34 (5 self)
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The domain of spatiotemporal applications is a treasure trove of new types of data as well as queries. For designing and testing novel data types and access methods that will support these applications, large spatiotemporal datasets are needed. As in many cases it is not possible to obtain real datasets, either they do not exist or they are not accessible, synthetic datasets are governed by artificial parameters rather than by the (sometimes invisible) rules governing real-world behavior. In this work we show how, at least for some cases, one can generate spatiotemporal datasets that simulate real-world behavior. We illustrate example cases and translate them into appropriate calls of GSTD, a spatiotemporal data generator. The generated data is illustrated using two-dimensional snapshot pictures as well as three-dimensional (two spatial plus one temporal dimension) trajectory images.
Robust Similarity Measures for Mobile Object Trajectories
- Proc. of DEXA Workshops
, 2002
"... We investigate techniques for similarity analysis of spatio-temporal trajectories for mobile objects. Such kind of data may contain a great amount of outliers, which degrades the performance of Euclidean and Time Warping Distance. Therefore, here we propose the use of non-metric distance functions b ..."
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Cited by 31 (1 self)
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We investigate techniques for similarity analysis of spatio-temporal trajectories for mobile objects. Such kind of data may contain a great amount of outliers, which degrades the performance of Euclidean and Time Warping Distance. Therefore, here we propose the use of non-metric distance functions based on the Longest Common Subsequence (LCSS), in conjunction with a sigmoidal matching function. Finally, we compare these new methods to various L p Norms and also to Time Warping distance (for real and synthetic data) and we present experimental results that validate the accuracy and efficiency of our approach, especially under the strong presence of noise.
Broadcast Data Allocation for Efficient Access of Multiple Data Items in Mobile Environments
- ACM Mobile Networks and Applications
, 2003
"... The issue of data broadcast has received much attention in mobile computing. A periodic broadcast of frequently requested data can reduce the workload of the up-link channel and facilitate data access for the mobile user. Many approaches have been proposed to schedule data items for broadcasting. Ho ..."
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Cited by 24 (1 self)
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The issue of data broadcast has received much attention in mobile computing. A periodic broadcast of frequently requested data can reduce the workload of the up-link channel and facilitate data access for the mobile user. Many approaches have been proposed to schedule data items for broadcasting. However, the issues of accessing multiple data items on the broadcast channel are less discussed. Two problems are discussed in this paper, that is, deciding the content of the broadcast channel based on the queries from the clients, and scheduling the data items to be broadcast. We will show that these two problems are NP-complete. Different heuristics to these problems are presented and compared through performance evaluations.
Peer-to-Peer Cooperative Caching in Mobile Environments
- IEEE Computer Society
"... An infrastructure-based mobile environment is formed with a wireless network connecting mobile hosts (MHs) and mobile support stations (MSSs). MHs are clients equipped with portable devices, such as laptops, personal digital assistants, cellular phones and so on, while MSSs are stationary servers pr ..."
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Cited by 21 (1 self)
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An infrastructure-based mobile environment is formed with a wireless network connecting mobile hosts (MHs) and mobile support stations (MSSs). MHs are clients equipped with portable devices, such as laptops, personal digital assistants, cellular phones and so on, while MSSs are stationary servers provid-ing information access for the MHs residing in their service areas. The recent widespread deployment of
Proactive caching for spatial queries in mobile environments
- Data Engineering, 2005. ICDE 2005. Proceedings. 21st International Conference on
, 2005
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On the Effect of Group Mobility to Data Replication in Ad-Hoc Networks
- IEEE Trans. Mobile Computing
, 2006
"... The growth in wireless communication technologies attracts a considerable amount of attention in mobile ad-hoc networks. Since mobile hosts in an ad-hoc network usually move freely, the topol-ogy of the network changes dynamically and disconnection occurs frequently. These characteristics make a mob ..."
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Cited by 15 (0 self)
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The growth in wireless communication technologies attracts a considerable amount of attention in mobile ad-hoc networks. Since mobile hosts in an ad-hoc network usually move freely, the topol-ogy of the network changes dynamically and disconnection occurs frequently. These characteristics make a mobile ad-hoc network be likely to be separated into several disconnected partitions, and the data accessibility is hence reduced. Several schemes are proposed to alleviate the reduction of data accessibility by replicating data items. However, little research effort was elaborated upon exploiting the group mobility where the group mobility refers to the phenomenon that several mo-bile nodes tend to move together. In this paper, we address the problem of replica allocation in a mobile ad-hoc network by exploring group mobility. We first analyze the group mobility model and derive several theoretical results. In light of these results, we propose a replica allocation scheme to improve the data accessibility. Several experiments are conducted to evaluate the performance of the proposed scheme. The experimental results show that the proposed scheme is able to not only obtain higher data accessibility but also produce lower network traffic than prior schemes.
Stabilizing Consensus in Mobile Networks
- IN DCOSS
, 2006
"... Inspired by the characteristics of biologically-motivated systems consisting of autonomous agents, we define the notion of stabilizing consensus in fully decentralized and highly dynamic ad hoc systems. Stabilizing consensus requires non-faulty nodes to eventually agree on one of their inputs, bu ..."
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Cited by 15 (1 self)
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Inspired by the characteristics of biologically-motivated systems consisting of autonomous agents, we define the notion of stabilizing consensus in fully decentralized and highly dynamic ad hoc systems. Stabilizing consensus requires non-faulty nodes to eventually agree on one of their inputs, but individual nodes do not necessarily know when agreement is reached. First we show that, similar to the original consensus problem in the synchronous model, there exist deterministic solutions to the stabilizing consensus problem tolerating crash faults. Similarly, stabilizing consensus can also be solved deterministically in presence of Byzantine faults with the assumption that n > 3f where n is the number of nodes and f is the number of faulty nodes. Our main result is a Byzantine consensus protocol in a model in which the input to each node can change finitely many times during execution and eventually stabilizes. Finally we present an impossibility result for stabilizing consensus in systems of identical nodes.
