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Computers, IEEE Transactions on

Issue 10 • Date Oct. 2002

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Displaying Results 1 - 14 of 14
  • Guest editorial: special section on data management systems and mobile computing

    Page(s): 1121 - 1123
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    Freely Available from IEEE
  • Query indexing and velocity constrained indexing: scalable techniques for continuous queries on moving objects

    Page(s): 1124 - 1140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (525 KB) |  | HTML iconHTML  

    Moving object environments are characterized by large numbers of moving objects and numerous concurrent continuous queries over these objects. Efficient evaluation of these queries in response to the movement of the objects is critical for supporting acceptable response times. In such environments, the traditional approach of building an index on the objects (data) suffers from the need for frequent updates and thereby results in poor performance. In fact, a brute force, no-index strategy yields better performance in many cases. Neither the traditional approach nor the brute force strategy achieve reasonable query processing times. This paper develops novel techniques for the efficient and scalable evaluation of multiple continuous queries on moving objects. Our solution leverages two complimentary techniques: Query Indexing and Velocity Constrained Indexing (VCI). Query Indexing relies on 1) incremental evaluation, 2) reversing the role of queries and data, and 3) exploiting the relative locations of objects and queries. VCI takes advantage of the maximum possible speed of objects in order to delay the expensive operation of updating an index to reflect the movement of objects. In contrast to an earlier technique that requires exact knowledge about the movement of the objects, VCI does not rely on such information. While Query Indexing outperforms VCI, it does not efficiently handle the arrival of new queries. Velocity constrained indexing, on the other hand, is unaffected by changes in queries. We demonstrate that a combination of Query Indexing and Velocity Constrained Indexing enables the scalable execution of insertion and deletion of queries in addition to processing ongoing queries. We also develop several optimizations and present a detailed experimental evaluation of our techniques. The experimental results show that the proposed schemes outperform the traditional approaches by almost two orders of magnitude. View full abstract»

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  • Efficient data allocation over multiple channels at broadcast servers

    Page(s): 1231 - 1236
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (622 KB) |  | HTML iconHTML  

    Broadcast is a scalable way of disseminating data because broadcasting an item satisfies all outstanding client requests for it. However, because the transmission medium is shared, individual requests may have high response times. In this paper, we show how to minimize the average response time given multiple broadcast channels by optimally partitioning data among them. We also offer an approximation algorithm that is less complex than the optimal and show that its performance is near-optimal for a wide range of parameters. Finally, we briefly discuss the extensibility of our work with two simple, yet seldom researched extensions, namely, handling varying sized items and generating single channel schedules. View full abstract»

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  • Processing distributed mobile queries with interleaved remote mobile joins

    Page(s): 1182 - 1195
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (877 KB) |  | HTML iconHTML  

    The query processing in a mobile computing environment involves join processing among different sites which include static servers and mobile computers. Because of the presence of asymmetric features in a mobile computing environment, the conventional query processing for a distributed database cannot be directly applied to a mobile computing system. In this paper, we first explore some unique features of a mobile environment and then, in light of these features, devise query processing methods for both join and query processing. Remote mobile joins are said to be effectual if they are, when being interleaved into a join sequence, able to reduce the amount of data transmission cost required for distributed mobile query processing. Since mobile relations are employed as reducers in our proposed query processing cost model, more mobile joins in the query processing lead to less data transmitted through the network. With proper scheduling, interleaving effectual remote mobile joins into a query scheduling can significantly reduce the total amount of data transmission among different sites. A simulator is developed to evaluate the performance of algorithms devised. Our results show that the approach of interleaving the processing of distributed mobile queries with effectual remote mobile joins is not only efficient, but also effective in reducing the total amount of data transmission cost required to process distributed mobile queries. View full abstract»

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  • General modeling and performance analysis for location management in wireless mobile networks

    Page(s): 1169 - 1181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB) |  | HTML iconHTML  

    Location management plays a significant role in current and future wireless mobile networks in effectively delivering services to the mobile users on the move. Many schemes have been proposed and investigated extensively in the last decade. However, most performance analyses were carried out either under simplistic assumptions on some time variables or via simulations. In this paper, we present a new analytical approach to investigate the tradeoff (cost) analysis for location management schemes under fairly general assumption. For two specific location management schemes, Pointer Forwarding Scheme (PFS) and Two-Location Algorithm (TLA), we present analytical formulae to compute the total costs. These formulae are easy to compute. Numerical results show that the traditional exponential model approximation may lead to a wrong decision in the tradeoff analysis. However, our analytical results can be easily used to find the appropriate parameters in PFS and TLA. View full abstract»

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  • Data allocation on wireless broadcast channels for efficient query processing

    Page(s): 1237 - 1252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (826 KB) |  | HTML iconHTML  

    Data broadcast is an excellent method for efficient data dissemination in the mobile computing environment. The application domain of data broadcast will be widely expanded in the near future, where the client is expected to perform complex queries or transactions on the broadcast data. To reduce the access latency for processing the complex query, it is beneficial to place the data accessed in a query close to each other on the broadcast channel. In this paper, we propose an efficient algorithm to determine the allocation of the data on the broadcast channel such that frequently co-accessed data are not only allocated close to each other, but also in a particular order which optimizes the performance of query processing. Our mechanism is based on the well-known problem named optimal linear ordering. Experiments are performed to justify the benefit of our approach. View full abstract»

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  • On transaction processing with partial validation and timestamp ordering in mobile broadcast environments

    Page(s): 1196 - 1211
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1539 KB) |  | HTML iconHTML  

    Conventional concurrency control protocols are inapplicable in mobile broadcast environments due to a number of constraints of wireless communications. Previous studies are focused on efficient processing of read-only transactions at the mobile clients, neglecting update transactions. In this paper, we design a new protocol for processing both read-only and update mobile transactions. The protocol can detect data conflicts at an early stage at the mobile clients and resolve data conflicts flexibly using dynamic adjustment of timestamp ordering. Early data conflict detection saves processing and communication resources, while dynamic adjustment of timestamp ordering allows more schedules of transaction executions such that unnecessary transaction aborts can be avoided. We performed extensive simulation studies to evaluate the effectiveness of these two features for the performance of the new protocol. The analysis of simulation results showed that both features are effective and contribute differently to the satisfactory performance of the protocol. View full abstract»

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  • Implementing automatic location update for follow-me database using VoIP and bluetooth technologies

    Page(s): 1154 - 1168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1026 KB) |  | HTML iconHTML  

    Personal Number (PN) service or Follow-me service allows a user to access telecommunication services with any terminal (e.g., fixed telephones or mobile phones) in any location within the service area. To provide this feature, the PN user needs to manually register with a phone number every time he/she enters a new location. If the user forgets to register the new phone number, the incoming calls will be misrouted. To provide user-friendly follow-me service, this paper proposes an automatic follow-me service (AFS) approach that automatically updates the PN records in the Follow-me database. The significance of our approach is that AFS can be integrated with existing Follow-me databases to automate PIN services offered by different PSTN service providers. We show how AFS can be implemented by using the Voice over IP and Bluetooth technologies. Then, we propose an analytic model to investigate the performance of AFS. The analytic results are validated by simulation experiments. Our study suggests how to select polling frequency to optimize the AFS performance. View full abstract»

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  • Multiversion data broadcast

    Page(s): 1224 - 1230
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB) |  | HTML iconHTML  

    Recently, broadcasting has attracted considerable attention as a means of disseminating information to large client populations in both wired and wireless settings. In this paper, we consider broadcasting multiple versions of data items to increase the concurrency of client transactions in the presence of updates. We introduce various techniques for organizing multiple versions on the broadcast channel. Performance results show that the overhead of supporting multiple versions can be kept low while providing a considerable increase in concurrency. Besides increasing the concurrency of client transactions, multiversion broadcast provides clients with the possibility of accessing multiple server states in a single broadcast cycle. Furthermore, multiversioning increases the tolerance of client transactions of disconnections from the broadcast channel. View full abstract»

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  • Cache invalidation and replacement strategies for location-dependent data in mobile environments

    Page(s): 1141 - 1153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB) |  | HTML iconHTML  

    Mobile location-dependent information services (LDISs) have become increasingly popular in recent years. However, data caching strategies for LDISs have thus far received little attention. In this paper, we study the issues of cache invalidation and cache replacement for location-dependent data under a geometric location model. We introduce a new performance criterion, called caching efficiency, and propose a generic method for location-dependent cache invalidation strategies. In addition, two cache replacement policies, PA and PAID, are proposed. Unlike the conventional replacement policies, PA and PAID take into consideration the valid scope area of a data value. We conduct a series of simulation experiments to study the performance of the proposed caching schemes. The experimental results show that the proposed location-dependent invalidation scheme is very effective and the PA and PAID policies significantly outperform the conventional replacement policies. View full abstract»

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  • Semantic data broadcast for a mobile environment based on dynamic and adaptive chunking

    Page(s): 1253 - 1268
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2353 KB) |  | HTML iconHTML  

    Database broadcast is an effective and scalable approach to disseminate information of high affinity to a large collection of mobile clients. A common problem of existing broadcast approaches is the lack of knowledge for a client to determine if all data items satisfying its query could be obtained from the broadcast. We therefore propose a semantic-based broadcast approach. A semantic descriptor is attached to each broadcast unit, called a data chunk. This semantic descriptor allows a client to determine if a query can be answered entirely based on broadcast items and, if needed, identify the precise definition of the remaining items in the form of a "supplementary" query. Data chunks can be of static or dynamic sizes and organized hierarchically. Their boundary can be determined on-the-fly, adaptive to the nature of client queries. We investigate different ways of organizing the data chunks over a broadcast channel to improve access performance. We introduce the data affinity index metric, which more accurately reflects client-perceived performance. A simulation model is built to evaluate our semantic-based broadcast schemes. View full abstract»

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  • Loop restructuring for data I/O minimization on limited on-chip memory embedded processors

    Page(s): 1269 - 1280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    In this paper, we propose a framework for analyzing the flow of values and their reuse in loop nests to minimize data traffic under the constraints of limited on-chip memory capacity and dependences. Our analysis first undertakes fusion of possible loop nests intra-procedurally and then performs loop distribution. The analysis discovers the closeness factor of two statements which is a quantitative measure of data traffic saved per unit memory occupied if the statements were under the same loop nest over the case where they are under different loop nests. We then develop a greedy algorithm which traverses the program dependence graph to group statements together under the same loop nest legally to promote maximal reuse per unit of memory occupied. We implemented our framework in Petit, a tool for dependence analysis and loop transformations. We compared our method with one based on tiling of fused loop nest and one based on a greedy strategy to purely maximize reuse. We show that our methods work better than both of these strategies in most cases for processors such as TMS320Cxx, which have a very limited amount of on-chip memory. The improvements in data I/O range from 10 to 30 percent over tiling and from 10 to 40 percent over maximal reuse for JPEG loops. View full abstract»

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  • Support for recovery in mobile systems

    Page(s): 1219 - 1224
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (273 KB) |  | HTML iconHTML  

    Mobile systems increasingly are being used for production-grade data-centered applications which require system support for transactional properties. For mobile applications, transactions can hide, to some extent, the infrastructure intrinsic to mobile systems, such as disconnection from the network, dozing, and storage limitations. In this paper, we introduce a framework to understand, specify, and reason about recovery support for transactional functionality, based on the notion of guarantees (promises one subsystem makes to another) and protocols (prescriptions for correct behavior). We apply our framework to a simple mobile system scenario, yielding an abstract specification that exposes the role of each component in achieving specific transactional semantics support, such as the redo-ability of committed updates that might be lost due to a failure; it also reveals unstated assumptions necessary for the correctness of recovery support. We also show how to reason about alternative ways of obtaining the desired transactional support and the requirements on the components to support recovery and transactions. View full abstract»

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  • TCOT-a timeout-based mobile transaction commitment protocol

    Page(s): 1212 - 1218
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    We present a transaction commit protocol, "Transaction Commit On Timeout (TCOT)," based on a "timeout" approach for Mobile Database Systems (MDS), which can be universally used to reach a final transaction termination decision (e.g., commit, abort, etc.) in any message-oriented system. Particularly suited for a wireless environment, a timeout mechanism is the only way to minimize the impact of the slow and unreliable wireless link. We compare TCOT to a modified version of 2PC to show its superiority based on commit time. View full abstract»

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Aims & Scope

The IEEE Transactions on Computers is a monthly publication with a wide distribution to researchers, developers, technical managers, and educators in the computer field.

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Meet Our Editors

Editor-in-Chief
Albert Y. Zomaya
School of Information Technologies
Building J12
The University of Sydney
Sydney, NSW 2006, Australia
http://www.cs.usyd.edu.au/~zomaya
albert.zomaya@sydney.edu.au