Preventing Location-Based Identity Inference in Anonymous Spatial Queries

The increasing trend of embedding positioning capabilities (for example, GPS) in mobile devices facilitates the widespread use of location-based services. For such applications to succeed, privacy and confidentiality are essential. Existing privacy-enhancing techniques rely on encryption to safeguard communication channels, and on pseudonyms to protect user identities. Nevertheless, the query contents may disclose the physical location of the user. In this paper, we present a framework for preventing location-based identity inference of users who issue spatial queries to location-based services. We propose transformations based on the well-established K-anonymity concept to compute exact answers for range and nearest neighbor search, without revealing the query source. Our methods optimize the entire process of anonymizing the requests and processing the transformed spatial queries. Extensive experimental studies suggest that the proposed techniques are applicable to real-life scenarios with numerous mobile users.     

Handling High-Level Queries in Location-Based Services for User Groups

In this paper we deal with the high level management of data involved in Location-Based Services in order to accommodate corresponding queries. A series of techniques are employed on major components of an LBS, namely mobile users, application environment and selected services. First, a grouping technique generalizes the spatio-temporal data describing the mobile users' movement. The environment is represented under a combined spatial and content hierarchy according to the application at hand. Finally, in the service component, relational operators are formed to support relative spatio-temporal queries, while lifeline data types are constructed to extract and compare behavioral trend patterns among the formed user groups. We show how all proposed techniques communicate under a common database schema. Answers to characteristic queries demonstrate the applicability of this work.     

Nearest Neighbor Queries in Shared-Nothing Environments

In this paper, we propose an efficient solution to the problem of nearest neighbor query processing in declustered spatial databases. Recently a branch-and-bound nearest neighbor finding (BB-NNF) algorithm has been designed to process nearest neighbor queries in R-trees. However, this algorithm is strictly serial (branch-and-bound oriented) and its performance degrades, during processing of a nearest neighbor query, if applied to a parallel environment, since it does not exploit any kind of parallelization. We develop an efficient query processing strategy for parallel nearest neighbor finding (P-NNF), assuming a shared nothing multi-processor architecture, where the processors communicate via a network. In our method, the relevant sites are activated simultaneously. In order to achieve this goal, statistical information is used. The efficiency measure is the response time of a given query. Experimental results, based on real-life and synthetic datasets, show that the proposed method outperforms the branch-and-bound method by factors.     

Effcient Distributed Skyline Queries for Mobile Applications

In this paper, we consider skyline queries in a mobile and distributed environment, where data objects are distributed in some sites (database servers) which are interconnected through a high-speed wired network, and queries are issued by mobile units (laptop, cell phone, etc.) which access the data objects of database servers by wireless channels. The inherent properties of mobile computing environment such as mobility, limited wireless bandwidth, frequent disconnection, make skyline queries more complicat...     

手机客户端食品添加剂查询系统初探

“民以食为天”,近年来食品安全问题在我国得到了巨大的关注,接连不断发生的恶性食品安全事故促使我们必须采取有效措施有效遏制在食品生产经营中滥用食品添加剂行为。本文对通过手机客户端食品添加刺查询系统的建设原则、建设目标及平台设计等方面进行了初步探讨。     

Collaborative Multimedia Presentations in Mobile Environments

Distributed multimedia documents systems, distributed video servers are examples of multimedia presentations involving collaboration among multiple information sources. In such applications, objects have to be retrieved from their sources and presented to users according to specified temporal relationships. Objects retrieval in these collaborative applications is influenced by their presentation times, durations, and network throughput available to their sources. Replication of objects amongst the set of collaborating systems gives a choice for object retrieval. Client going through a multimedia presentation can be in a mobile environment. Here, object retrievals from collaborating servers are carried out by base stations to which the client is attached. Mobile client then downloads objects from the base station.In this paper, we present a graph-search based algorithm for computing and negotiating throughput requirements of collaborating multimedia presentations with replicated objects in a mobile environment. This algorithm maximizes the number of cached objects (that have already been played) for handling operations such as reverse presentation.     

Cost Estimation for Queries Experiencing Multiple Contention States in Dynamic Multidatabase Environments

Accurate query cost estimation is crucial to query optimization in a multidatabase system. Several estimation techniques for a static environment have been suggested in the literature. To develop a cost model for a dynamic environment, we recently introduced a multistate query-sampling method. It has been shown that this technique is promising in estimating the cost ofa query run in any given contention state for a dynamic environment. In this paper, we study a new problem on how to estimate the cost of a large query that may experience multiple contention states. Following the discussion of limitations for two simple approaches, i.e., single state analysis and average cost analysis, we propose two novel techniques to tackle this challenge. The first one, called fractional analysis, is suitable for a gradually and smoothly changing environment, while the second one, called the probabilistic approach, is developed for a rapidly and randomly changing environment. The former estimates a query cost by analyzing its fractions, and the latter estimates a query cost based on Markov chain theory. The related issues including cost formula development, error analysis, and comparison among different approaches are discussed. Experiments demonstrate that the proposed techniques are quite promising in solving the new problem. Received 5 January 2001 / Revised 6 June 2001 / Accepted in revised form 9 July 2001 Correspondence and offprint requests to: Qiang Zhu, Department of Computer and Information Science, The University of Michigan – Dearborn, Dearborn, MI 48128, USA. Email: qzhu@umich.eduau     

移动计算中基于Mobile Agent的数据库访问技术

本文针对传统基于应用程序方式的数据库机制在移动计算环境中所存在的不足，分别提出了移动计算环境中基于Mobile Agent的集中式数据库和分布式异种数据库访问技术，并利用IBM开发的Aglets在一个宽带无线IP网络上进行了原理实验，实验结果表明这种技术在移动计算环境中明显提高了数据库访问的性能。     

Data Consistency for Cooperative Caching in Mobile Environments

The trend toward wireless communications and advances in mobile technologies are increasing consumer demand for ubiquitous access to Internet-based information and services. A 3D framework provides a basis for designing, analyzing, and evaluating strategies to address data consistency issues in mobile wireless environments. A proposed relay-peer-based cache consistency protocol offers a generic and flexible method for carrying out cache invalidation     

Location-Based Services

Today, location information is in the hands of the masses. The success of location in pervasive computing has exposed new challenges and opportunities for researchers including making location sensing more robust, accurate, deployable, secure, and developer-friendly. This special issue showcases papers that describe recent research that addresses these challenges.     

Efficient Processing of Continual Range Queries for Location-Aware Mobile Services

Efficient processing of continual range queries is important in providing location-aware mobile services. In this paper, we study a new main memory-based approach to indexing continual range queries to support location-aware mobile services. The query index is used to quickly answer the following question continually: “Which moving objects are currently located inside the boundaries of individual queries?” We present a covering tile-based (COVET) query index. A set of virtual tiles are predefined, each with a unique ID. One or more of the virtual tiles are used to strictly cover the region defined by an individual range query. The query ID is inserted into the ID lists associated with the covering tiles. These covering tiles touch each other only at the edges. A COVET index maintains a mapping between a covering tile and all the queries that contain that tile. For any object position, search is conducted indirectly via the covering tiles. More importantly, a COVET-based query index allows query evaluation to take advantage of incremental changes in object locations. Computation can be saved for those objects that have not moved outside the boundaries of covering tiles. Simulations are conducted to evaluate the effectiveness of the COVET index and compare virtual tiles of different shapes and sizes.     

一种基于移动环境的语义缓存一致性维护技术

在深入研究缓存失效广播技术和语义缓存的基础上,提出了一种新的基于移动环境的语义缓存一致性维护技术——基于语义缓存的异步有状态（BSCAS）技术。BSCAS技术可以支持移动客户的各种断接方式,减少无线通信的开销,让移动客户有更好的自治性。     

无线移动环境中的拉式实时并发控制机制

考虑到诸如带宽、移动性、频繁断接等限制,传统可串行化并发控制协议显得过于严格而无法满足移动实时数据库环境的要求。该文首先形式化定义并分析了弱可串行化正确性准则,弱可串行化比传统冲突可串行化宽松且能始终保证数据库的一致性。进而给出了一种适宜于移动实时数据库的弱可串行化并发控制协议WMHP-2PL。最后性能实验证实了新协议的有效性。     

Light-Weight Currency Management Mechanisms in Mobile and Weakly-Connected Environments

This paper discusses the currency management mechanisms used in Deno, an object replication system designed for use in mobile and weakly-connected environments. Deno primarily differs from previous work in implementing an asynchronous weighted-voting scheme via epidemic information flow, and in committing updates in an entirely decentralized fashion, without requiring any server to have complete knowledge of system membership.We first give an overview of Deno, discussing its voting scheme, proxy mechanism, basic API, and commit performance. We then focus on the issue of currency management. Although there has been much work on currency management in synchronous, strongly-connected environments, this issue has not been explored in asynchronous, weakly-connected environments. We present currency management mechanisms, based on peer-to-peer currency exchanges, that enable light-weight replica creation, retirement, and currency redistribution while maintaining the correctness of the underlying consistency protocol. We also demonstrate that peer-to-peer currency exchanges can be used to exponentially converge to arbitrary target currency distributions, without the need for any server to have global system information.     

Fuzzy Motion Planning of Mobile Robots in Unknown Environments

A fuzzy algorithm is proposed to navigate a mobile robot from a given initial configuration to a desired final configuration in an unknown environment filled with obstacles. The mobile robot is equipped with an electronic compass and two optical encoders for dead-reckoning, and two ultrasonic modules for self-localization and environment recognition. From the readings of sensors at every sampling instant, the proposed fuzzy algorithm will determine the priorities of thirteen possible heading directions. Then the robot is driven to an intermediate configuration along the heading direction that has the highest priority. The navigation procedure will be iterated until a collision-free path between the initial and the final configurations is found. To show the feasibility of the proposed method, in addition to computer simulation, experimental results will be also given.     

移动计算环境中并发控制协议的研究

提出了多版本乐观并发控制协议(MVOCC),缩短了只读事务的响应时间,减少了通信开销,避免了不必要的事务重启动。实验结果表明该协议优于OCC协议和TO协议。     

动态环境中移动机器人地图构建的研究进展

大部分现有的移动机器人地图构建方法都是基于静态环境的假设,而实际应用中移动机器人的工作环境是随时间变化的.综述了动态环境中移动机器人地图构建的最新研究进展,介绍了基于地图、基于运动和基于跟踪的检测动态障碍物的各种方法,分析比较了动态环境中移动机器人过滤运动障碍物传感器观测信息和结合运动障碍物传感器观测信息构建环境地图的主要方法,并总结了各种方法的优缺点.探讨了动态环境中移动机器人地图构建存在的难点问题,并展望了该领域的研究方向.     

Global Level Path Planning for Mobile Robots in Dynamic Environments

This paper presents a self-adapting approach to global level path planning in dynamic environments. The aim of this work is to minimize risk and delays in possible applications of mobile robots (e.g., in industrial processes). We introduce a hybrid system that uses case-based reasoning as well as grid-based maps for decision-making. Maps are used to suggest several alternative paths between specific start and goal point. The casebase stores these solutions and remembers their characteristics. Environment representation and casebase design are discussed. To solve the problem of exploration vs. exploitation, a decision-making strategy is proposed that is based on the irreversibility of decisions. Forgetting strategies are discussed and evaluated in the context of case-based maintenance. The adaptability of the system is evaluated in a domain based on real sensor data with simulated occupancy probabilities. Forgetting strategies and decision-making strategies are evaluated in simulated environments. Experiments show that a robot is able to adapt in dynamic environments and can learn to use paths that are less risky to follow.