Distributed location-based query processing on large volumes of moving items

Recently, new techniques to efficiently manage current and past location information of moving objects have received significant interests in the area of moving object databases and location-based service systems. In this paper, we exploit query processing schemes for location management systems, which consist of multiple data processing nodes to handle massive volume of moving objects such as cellular phone users.To show the usefulness of the proposed schemes, some experimental results showing performance factors regarding distributed query processing are explained. In our experiments, we use two kinds of data set: one is generated by the extended GSTD simulator and another is generated by the real-time data generator which generates location sensing reports of various types of users having different movement patterns.     

考虑运动对象位置不确定性的位置管理策略

以传统轨道模型为基础,观测构造运动对象历史信息统计样本并分析其特征,设计了基于样本统计的位置预测模型,更好地考虑了运动对象运动随机性的特点,提高了位置预测的准确性;然后在该模型的基础上设计了一种为管理运动对象位置不确定性而设定最佳阈值的方法,这种方法相对于传统的静态阈值策略减少了位置更新的信息代价开销;最后,采用一种基于时间和空间划分的Grid模型构造索引结构,给出了管理运动对象位置信息进行区域查询和kNN（k-Nearest Neighbor）查询的实现过程和算法,是一种进行运动对象位置相关查询的可行性方案.     

一种基于安全索引的位置隐私保护方法

基于位置的服务(location based services, LBS)为人们日常生活带来极大便利的同时也严重地威胁到用户的隐私.为了在保护用户位置隐私的同时降低用户的查询代价,提出了一种基于安全索引的位置隐私保护方法(location privacy protection method based on secure index, LPPMSI).LPPMSI不需要用户搜集数据信息,数据拥有者为虚假位置信息建立安全索引.用户能够安全、快速地检索到虚假位置信息,服务器再执行基于虚假位置的LBS.并且还提出了基于滑动窗口的候选位置选择算法,有效减少候选位置选择时间.实验结果表明,LPPMSI在不改变隐私保护能力的前提下,不需要用户花费大量时间搜集数据分布及查询概率信息.     

Tracking data management using topology of moving object database system for moving object constrained trajectory in LBS application

Advances in wireless technologies and positioning technologies and spread of wireless devices, an interest in LBS (Location Based Service) is arising. To provide location based service, tracking data should have been stored in moving object database management system (called MODBMS) with proper policies and managed efficiently. So the methods which acquire the location information at regular time intervals then, store and manage have been studied. In this paper, we suggest tracking data management techniques using topology that is corresponding to the moving path of moving object. In our techniques, we update the MODBMS when moving object arrived at a street intersection or a curved road which is represented as the node in topology and predict the location at past and future with attribute of topology and linear function. In this technique, location data that are corresponding to the node in topology are stored, thus reduce the number of update and amount of data. Also in case predicting the location, because topology are used as well as existing location information, accuracy for prediction is increased than applying linear function or spline function.     

公路网上移动对象连续k近邻查询的一种方法

公路网上移动对象连续k近邻查询是最近时空数据库查询中的一个研究热点,它是在一个时间段内找到离查询点最近的K个移动对象.我们分析了现有查询方法,存在的问题主要是运动对象位置随时间而频繁变化以至于不能及时更新运动对象的信息而导致返回KNN结果不正确.为了解决这些问题,采用一种距离预计算方法,使计算量减少,从而为更新通讯获得更多时间.通过实验证明,我们提出的方法是有效的.     

基于代理重加密的VANETs中安全位置服务

提供车辆位置服务是车载网络(vehicle ad hoc networks, VANETs)的重要应用。而用户(车辆行驶人)希望他的位置信息只能暴露于他授权的消息发送者,这就涉及位置隐私问题。提出基于代理重加密的安全位置服务算法(proxy re-encryption- based secure location service, PRESLS)。PRESLS算法采用中心管理模式,并由交通信息港(traffic information center, TIC)扮演中心管理者,且由TIC维持车辆轨迹数据,同时,TIC作为车辆与路边设施单元的中介,使得路边设施单元能安全地共享轨迹数据。利用代理重加密算法,使得轨迹数据不仅对未授权的实体,而且对TIC也是隐匿的,进而实现了位置数据所保密性。通过安全性能分析和基于地图位置服务(map-based location service, MBLS)的实验评估PRESLS算法的性能。分析表明,车辆能够控制仅由车辆允可的路边设施单元才能接入车辆的轨迹数据。同时,基于MBLS的实验数据表明,PRESLS算法在维持车辆轨迹数据安全的同时,并没有降低位置查询成功率。     

A shortest path algorithm for moving objects in spatial network databases

One of the most important kinds of queries in Spatial Network Databases （SNDB） to support location-based services （LBS） is the shortest path query. Given an object in a network, e.g. a location of a car on a road network, and a set of objects of interests, e.g. hotels, gas station, and car, the shortest path query returns the shortest path from the query object to interested objects. The studies of shortest path query have two kinds of ways, online processing and preprocessing. The studies of preprocessing suppose that the interest objects are static. This paper proposes a shortest path algorithm with a set of index structures to support the situation of moving objects. This algorithm can transform a dynamic problem to a static problem. In this paper we focus on road networks. However, our algorithms do not use any domain specific information, and therefore can be applied to any network, This algorithm＇s complexity is O（klog2i）, and traditional Diikstra＇s comolexitv is O（（i ＋ k）^2）.     

ORDBMS的新特性及其对查询优化的影响

讨论了ORDBMS的一些新特性,ORDBMS应该支持用户自定义的数据类型和函数;存储机制能够支持复杂对象或大对象;其索引结构必须是类属的;它还必须支持数据和函数的继承。讨论了这些特性对查询优化策略的影响,指出传统DBMS的优化策略将不能适应这些新特性,提出了基于成本的查询优化模型。     

分布式网络中 CKNN 查询的 BORA 优化汇聚

针对时空数据库中,移动对象轨迹的连续K近邻查询(continuous K nearest neighbor query,CKNN)的查询效率较低的问题,以及在分布式的移动对象数据库(moving objects databases,MOD)环境下,提升对应查询结果的数据汇聚效率问题进行了研究.在CKNN查询中,设计优化了查询海滩线的更新算法,通过在轨迹数据结构中增加更新标志位,减少了轨迹线段参与的判定运算;同时在假设的类网格覆盖的分布式空间环境下,利用基于Bresenham覆盖的路由汇聚(Bresenham-based overlay for routing and aggregation,BORA)方法,进行查询结果的汇聚;并针对不同近邻参数、轨迹数目、移动对象速度、汇聚方式等对查询时间的影响进行了仿真实验;仿真结果表明,不同参数数值的增加延长了处理时间,基于BORA的汇聚方式比一般的汇聚方式节省了更多的处理时间,提高了系统查询及处理的效率.     

基于幂次变换和区域收缩算法的运动目标检测与定位

运动目标分割与跟踪是计算机视觉中的重要研究课题,而目标检测与定位是其中的必要步骤,对分割与跟踪效果影响很大.在此提出一种新的运动目标检测与定位方法,该方法在差分二值图像上,通过区域收缩定位到运动像素密度较大的区域,从而实现运动目标定位.在多目标情况下,先通过幂次变换突出不同位置的目标,然后再通过区域收缩实现目标定位,给出目标的特征矩形,便于进一步的跟踪与识别.该方法不需要任何关于目标数的先验知识,对噪声鲁棒性较强.文中给出的实验结果证明该算法的有效性.     

数据集成系统中数据源描述的框架方法

查询重组是数据集成系统中必不可少的模块之一 ,关于数据源的内容以及它们之间联系的描述 ,是其首要任务 .在基于IA(InformationAgent)的数据集成系统中 ,可以利用多Agent系统中的匹配 (Matchmaking)机制来实现查询重组 ,本文首先给出在这种环境下查询重组模块的工作流程 ,然后提出一种知识表示中的框架来描述数据源和用户查询 ,以便系统高效地进行框架匹配和查询改写     

移动对象的建模和查询

本文提出一种离散时空轨迹模型来表示数据库系统中的移动对象的方法。这种模型不仅支持过去和现在位置信息的查询，而且支持未来查询。     

时空数据模型的初步设计

时空数据库用于模拟和查询位置或形状随时间改变的移动对象。提出了用于表示移动对象的时空数据类型和扩展数据类型。并在此基础上,对时空操作符也作了相应的概括。该数据模型便于实现,并能较好地支持时空查询。     

时空数据模型的初步设计

时空数据库用于模拟和查询位置或形状随时间改变的移动对象。提出了用于表示移动对象的时空数据类型和扩展数据类型。并在此基础上，对时空操作符也作了相应的概括。该数据模型便于实现，并能较好地支持时空查询。     

LBS系统安全性

LBS（基于位置服务）是利用移动用户的位置信息,为用户提供的一种新型的增值服务。用户位置信息具有天然的敏感性,加之目前专门针对LBS的政策法规的缺位,如何防止用户位置信息的泄露便成为一个亟待解决的问题。对此,该文首先通过分析LBS系统的架构、服务流程来阐述目前已经应用于LBS系统的安全隐私保护措施。之后提出一些目前仍然...     

基于双树双索引结构的移动查询方法

为实现对有限范围内海量移动对象的有效索引,构建通用的移动查询解决方案,针对移动对象在道路网格中的运动特点,提出了预测实时运动速度的速度积累模型和预测未来聚集位置的基于双树双索引结构的移动对象查询方法.双树双索引结构利用网格划分思想构建空间分割树,实现对现有GG TPR-tree查询结构的拓展,并结合GG TPR-tree索引及建立于内存中的Hash索引以满足各种类型的移动查询请求.仿真实验表明,在回答受限范围内海量移动对象的确定性查询和统计性查询时,与传统方法相比,双树双索引结构在查询结果准确率方面有明显的改善.     

移动对象时空拓扑关系模型

时空拓扑关系是移动对象时空特性研究的一个重要内容。针对二维欧氏空间内的平面移动对象,建立基于时间片的时空数据模型。并基于点集理论定义移动对象时空拓扑关系的定性模型,表达为由9交模型描述的时态拓扑关系和空间拓扑关系的复合。同时提出其时空拓扑有效性、可计算性约束及其计算规则,进而给出移动对象动态时空特征的表达方法。该模型提出了一种移动对象时空拓扑关系的表达和计算方法,有效的刻画其动态特征,可以为移动对象数据库及其时空查询提供理论基础     

数据流管理系统关键技术研究

传统数据库系统用于需要持久稳固的数据存储和复杂查询的应用,然而近几年许多的应用证明这种数据模式和查询范例是不适合的,如传感器数据位置跟踪、工厂装配线管理、金融证券管理、Internet流量监控、Web使用日志、电话呼叫记录、和事务日志的在线分析等,在这些应用背景中信息按照数据值序列的形式自然产生,都需要及时地处理大规模的潜在快速的异步的数据流.本文回顾近来数据流管理系统领域的相关工作和流项目的研究情况;分析了连续查询处理的新需求和挑战;重点研究包括数据模式,系统结构,连续查询语言,调度方法,相关算法和查询评价等关键技术.     

Indexing large moving objects from past to future with PCFI

In moving object database, the moving objects' current position must be kept in memory, also to the trajectory, in some case, as same as the future. But the current existing indexes such as SEB tree, SETI tree, 2+3R tree, 2 3RT tree and etc. can only provide the capability for past and current query, and the TPR Tree, TPR * Tree and etc. can only provide the capability for current and future query. None of them can provide a strategy for indexing the past, current and also the future information of moving objects. In this paper, we propose the past current future Index (PCFI Index) to index the past, current & future information of the moving objects. It is the combination of SETI tree and TPR * tree, the SETI liking index is used for indexing the historical trajectory segments except the front line structure, and the moving objects' current positions, velocities are indexed via the in memory frontline structure which mainly implemented with TPR * tree. Considering the large update operations on TPR tree of large population, a hash table considering cache sensitivity is also introduced. It works with the frontline part, leading a bottom up update of the tree. The performance analysis proves that the PCFI index can handle most of the query efficiently and provides a uniform solution for the trajectory query, time slice query, internal query and moving query.     

Tracking data management using topology of moving object database system for moving object constrained trajectory in LBS application

Advances in wireless technologies and positioning technologies and spread of wireless devices, an interest in LBS (Location Based Service) is arising. To provide location based service, tracking data should have been stored in moving object database management system (called MODBMS) with proper policies and managed efficiently. So the methods which acquire the location information at regular time intervals then, store and manage have been studied. In this paper, we suggest tracking data management techniques using topology that is corresponding to the moving path of moving object. In our techniques, we update the MODBMS when moving object arrived at a street intersection or a curved road which is represented as the node in topology and predict the location at past and future with attribute of topology and linear function. In this technique, location data that are corresponding to the node in topology are stored, thus reduce the number of update and amount of data. Also in case predicting the location,because topology are used as well as existing location information, accuracy for prediction is increased than applying linear function or spline function.