移动数据库及其关键技术

本文介绍支持移动计算环境的新一代分布式数据库技术,即移动数据库,包括它的基本概念、系统模型和实现目标。并通过对移动数据库的二级复制体系结构的分析,指出了它的关键技术。     

嵌入式移动数据库中的移动Agent问题探讨

随着互联网络技术和无线通信技术的发展,嵌入式移动数据库技术已成为目前数据库领域的一个新的研究分支,文中对移动Agent技术进行了概要说明,在此基础上讨论了将移动Agent技术应用于嵌入式移动数据库中的优势,探讨了基于移动Agent的嵌入式移动数据库的体系结构以及将移动Agent引入后它的研究侧重点。     

移动客户机的缓存同步算法

1.移动客户机缓存简介在移动数据库系统中,移动客户机(MobileClient,简称MC)的缓存技术可以用于支持MC的断接操作,即在MC与数据库服务器中断网络连接时,允许用户继续对数据库进行操作。与服务器级复制相比,MC的缓存属于次一级的地位,它与服务器级复制互相配合,共同支持MC对移动数据库的访问,从而提高移动数据库的可用性。     

嵌入式移动数据库的应用与研究

随着移动计算技术的发展,移动数据库逐步走向应用,在嵌入式操作系统中移动数据库更显示出其优越性。本文研究了移动数据库的概念及架构,分析了移动数据库在应用中关键点,指出了移动数据库应用的具体方向。     

基于动态网格的移动对象索引

在移动对象数据库中,移动对象的数量可能会经常变化,这就给索引技术提出了新的挑战。移动对象索引技术的效率是移动对象数据库的一个重要研究课题。为了防止数据库由于移动对象数量的变化而导致性能锐减,本文在网格文件索引的基础上提出了一种动态网格索引技术。通过实验比较显示,它相对于静态索引具有更好的适应性。     

嵌入式移动数据库的应用与研究

随着移动计算技术的发展,移动数据库逐步走向应用,在嵌入式操作系统中移动数据库更显示出其优越性.本文研究了移动数据库的概念及架构,分析了移动数据库在应用中关键点,指出了移动数据库应用的具体方向.     

嵌入式移动数据库探秘

目前．随着移动技术的发展及智能移动终端的普及，人们对移动数据库实时处理和管理要求不断提高，嵌入式移动数据库越来越体现其优越性。嵌入式移动数据库技术已经成为一个十分活跃的研究领域，并引起了越采越广泛的关注。本文阐述了嵌入式移动数据库的概念，应用环境的特点，厦其目标的实现，并探讨了嵌入式移动数据库的几种关键技术。     

移动数据库自适应缓存管理及应用

针对移动计算环境,提出移动数据库自适应缓存管理概念,给出移动数据库自适应缓存模型。针对移动位置服务提出弹性分组压缩位向量法,针对断接性提出主动夭折与通知确认机制相结合法。详细给出移动数据库自适应缓存调度算法及实现并通过移动手机预约挂号系统的应用验证该方法的有效性。实际运行结果表明它能大大改善移动应用响应时间、降低系统资源开销,在支持移动位置服务及断接性等方面具有较好的性能,从而提升移动应用整体性能。     

基于智能Agent技术构建移动数据库系统模型的研究与实现

现有的移动数据库体系大都是在传统的基于固定网络的分布式数据库技术的基础上进行改进,但是这些改进并不能真正满足需求,尤其是当移动用户规模变的十分巨大的时候,这些体系就会明显的暴露其缺陷。对Agent和Multi-Agent的研究近几年来已成为分布式人工智能研究的一个热点。Agent是具有拟人智能特性的、驻留与活动于客观世界中的实体。Agent技术的自主性、主动性、反应性、移动性和社会性等优良特性,使它非常适合移动计算环境,理所当然成为实现移动数据库体系的首选。该文系统、深入地研究了基于Agent的移动数据库体系的模型系统,并实现了其在移动业务处理系统中的一般应用。     

基于移动Agent嵌入式移动数据库系统的研究

介绍嵌入式移动数据库的概念及特点,针对嵌入式移动数据库在用户规模巨大时出现的不足,提出将移动代理应用于嵌入式移动数据库.接着分析了移动代理的特点和移动代理应用于嵌入式移动数据库的好处,最后详细讨论了基于移动代理的嵌入式移动数据库系统模型、系统结构和系统实现.     

A survey of data replication techniques for mobile ad hoc network databases

A mobile ad hoc network (MANET) is a network that allows mobile servers and clients to communicate in the absence of a fixed infrastructure. MANET is a fast growing area of research as it finds use in a variety of applications. In order to facilitate efficient data access and update, databases are deployed on MANETs. These databases that operate on MANETs are referred to as MANET databases. Since data availability in MANETs is affected by the mobility and power constraints of the servers and clients, data in MANETs are replicated. A number of data replication techniques have been proposed for MANET databases. This paper identifies issues involved in MANET data replication and attempts to classify existing MANET data replication techniques based on the issues they address. The attributes of the replication techniques are also tabulated to facilitate a feature comparison of the existing MANET data replication works. Parameters and performance metrics are also presented to measure the performance of MANET replication techniques. In addition, this paper also proposes criteria for selecting appropriate data replication techniques for various application requirements. Finally, the paper concludes with a discussion on future research directions.     

基于移动数据库的Mobile Agent应用模型研究

基于移动计算环境的特点,使传统的客户/服务器模型己不能满足需要,人们需要一种更加灵活的体系结构。近年来,关于Mobile Agent的研究引起了广泛的关注。本文提出了一个基于mobile agent的移动数据库模型和相应的体系结构。     

J2MEMicroDB: a new Open Source lightweight database engine for J2ME mobile devices

J2ME is the development platform for mobile devices with larger support and availability in the market right now. Due to the minimalist definition of this architecture it does include neither API’s for data persistence management, like object serialization, and relational database access nor standard APIs to access a remote host. This paper presents J2MEMicroDB, an Open Source software that implements object serialization, a local relational database engine on the mobile device and a remote database access protocol that allows access to any JDBC database. In the design and implementation of J2MEMicroDB specific requirements and limitation of mobile devices have been considered. Even some performance improvements have been developed, like BTree indexing structures which improves significantly the efficiency of the searches, as the presented cross-platform benchmarking proves.     

基于COSMOS的移动数据库同步过程建模

介绍了COSMOS的基本概念,并通过一个保险信息系统中数据同步建模的实例,论述了采用COSMOS为移动数据库同步过程建模的一般方法。     

An energy-efficient mobile transaction processing method using random back-off in wireless broadcast environments

Broadcast is widely accepted as an efficient technique for disseminating data to a large number of mobile clients over a single or multiple channels. Due to the limited uplink bandwidth from mobile clients to server, conventional concurrency control methods cannot be directly applied. There has been many researches on concurrency control methods for wireless broadcast environments. However, they are mostly for read-only transactions or do not consider exploiting cache. They also suffer from the repetitive aborts and restarts of mobile transactions when the access patterns of mobile transactions are skewed. In this paper, we propose a new optimistic concurrency control method suitable for mobile broadcast environments. To prevent the repetitive aborts and restarts of mobile transactions, we propose a random back-off technique. To exploit the cache on mobile clients, our method keeps the read data set of mobile transactions and prefetches those data items when the mobile transactions are restarted. As other existing optimistic concurrency control methods for mobile broadcast environments does, it works for both read-only and update transactions. Read-only transactions are validated and locally committed without using any uplink bandwidth. Update transactions are validated with forward and backward validation, and committed after final validation consuming a small amount of uplink bandwidth. Our performance analysis shows that it significantly decreases uplink and downlink bandwidth usage compared to other existing methods.     

Indexing mobile objects using dual transformations

With the recent advances in wireless networks, embedded systems, and GPS technology, databases that manage the location of moving objects have received increased interest. In this paper, we present indexing techniques for moving object databases. In particular, we propose methods to index moving objects in order to efficiently answer range queries about their current and future positions. This problem appears in real-life applications such as predicting future congestion areas in a highway system or allocating more bandwidth for areas where a high concentration of mobile phones is imminent. We address the problem in external memory and present dynamic solutions, both for the one-dimensional and the two-dimensional cases. Our approach transforms the problem into a dual space that is easier to index. Important in this dynamic environment is not only query performance but also the update processing, given the large number of moving objects that issue updates. We compare the dual-transformation approach with the TPR-tree, an efficient method for indexing moving objects that is based on time-parameterized index nodes. An experimental evaluation shows that the dual-transformation approach provides comparable query performance but has much faster update processing. Moreover, the dual method does not require establishing a predefined query horizon.Received: 27 April 2003, Accepted: 11 May 2004, Published online: 14 September 2004Edited by: J. VeijalainenGeorge Kollios: Supported by NSF CAREER Award 0133825.Dimitrios Gunopulos: Supported by NSF ITR 0220148, NSF CAREER Award 9984729, NSF IIS-9907477, and NRDRP.Vassilis J. Tsotras: Supported by NSF IIS-9907477, NSF EIA-9983445 and the DoD.     

Dealing with fuzziness in active mobile database systems

Current needs of industry required the development of advanced database models like active mobile database systems. An active mobile database system can be designed by incorporation of triggering rules into a mobile computing environment in which the users are able to access a collection of database services using mobile and non-mobile computers at any location. Fuzzy concepts are adapted to the field of databases in order to deal with ambiguous, uncertain data. Fuzziness comes into picture in active mobile databases especially with spatial queries on moving objects. Incorporating fuzziness into rules would also improve the effectiveness of active mobile databases as it provides much flexibility in defining rules for the supported application. In this paper we present some methods to adapt the concepts developed for fuzzy systems to active mobile databases.     

创建移动学习的多媒体组件

该文提出了一个基于模板的生成多媒体组件的方案,适用于应用计算机或移动设备的教学。该研究领域结合了计算机科学、移动设备和电子学习的研究,被称为移动学习或者M-Learning。研究的目标是为处于任何地点的学习者提供获取电子学习资料的途径,让学习内容更适合移动设备的特点、交流环境、学习者的知识和喜好。该技术解决方案将充分发挥移动设备的潜力,广泛应用于教育领域。     

A concurrency control scheme for mobile transactions in broadcast disk environments

Broadcast disk technique has been often used to disseminate frequently requested data efficiently to a large volume of mobile clients over wireless channels. In broadcast disk environments, a server often broadcasts different data items with differing frequencies to reflect the skewed data access patterns of mobile clients. Previously proposed concurrency control methods for mobile transactions in wireless broadcast environments are focused on the mobile transactions with uniform data access patterns. These protocols perform poorly in broadcast disk environments where the data access patterns of mobile transactions are skewed. In broadcast disk environments, the time length of a broadcast cycle usually becomes large to reflect the skewed data access patterns. This will often cause read-only transactions to access old data items rather than the latest data items. Furthermore, updating mobile transactions will be frequently aborted and restarted in the final validation stage due to the update conflict of the same data items with high access frequencies. This problem will increase the average response time of the update mobile transactions and waste the uplink communication bandwidth. In this paper, we extend the existing FBOCC concurrency control method to efficiently handle mobile transactions with skewed data access patterns in broadcast disk environments. Our method allows read-only transactions to access the more updated data, and reduces the average response time of updating transactions through early aborts and restarts. Our method also reduces the amount of uplink communication bandwidth for the final validation of the update transactions. We present an in-depth experimental analysis of our method by comparing with existing concurrency control protocols. Our performance analysis shows that it significantly decreases the average response time and the amount of uplink bandwidths over existing methods.     

An indexing scheme for energy-efficient processing of content-based retrieval queries on a wireless data stream

Wireless data broadcasting is a popular data delivery approach in mobile computing environments, where the broadcasting servers usually adopt indexing schemes for mobile clients to energy-efficiently access data on a wireless broadcast stream. However, conventional indexing schemes use primary key attribute values to construct tree structures. Therefore, these schemes do not support content-based retrieval queries such as partial-match queries and range-queries. This paper proposes an indexing method that supports content-based retrieval queries on a wireless data stream. The method uses a tree-structured index, called B2V-Tree, which is composed of bit-vectors that are generated from data records through multi-attribute hashing. Through analysis and experiments, the effectiveness of the proposed method is shown.