Energy-Efficient Mobile Cache Invalidation

Caching data in a wireless mobile computer can significantly reduce the bandwidth requirement. However, due to battery power limitation, a wireless mobile computer may often be forced to operate in a doze or even totally disconnected mode. As a result, the mobile computer may miss some cache invalidation reports. In this paper, we present an energy-efficient cache invalidation method for a wireless mobile computer. The new cache invalidation scheme is called grouping with cold update-set retention (GCORE). Upon waking up, a mobile computer checks its cache validity with the server. To reduce the bandwidth requirement for validity checking, data objects are partitioned into groups. However, instead of simply invalidating a group if any of the objects in the group has been updated, GCORE retains the cold update set of objects in a group if possible. We present an efficient implementation of GCORE and conduct simulations to evaluate its caching effectiveness. The results show that GCORE can substantially improve mobile caching by reducing the communication bandwidth (thus energy consumption) for query processing.     

移动数据库技术的缓存管理策略研究

移动数据库的缓存技术使客户机通过缓存少量的服务器数据项,便能拥有较高的处理速度,而且,它也是解决移动数据库频繁断接性问题的关键技术。文章研究了缓存管理策略在移动数据库中的应用,重点研究了缓存管理策略三大关键问题：缓存粒度、缓存一致性以及缓存替换,提出了一种基于统计与优先级原则解决缓存一致性问题的新思路。     

“Cache and Carry” for Location Management in Mobile Information Systems

Recent development of hardware technologies such as communication medium which advances from wired to wireless has led to the emergence of mobile information systems. A major problem in such a mobile information system is how to locate mobile clients. This is named the location management issue. Two major costs are involved in managing a mobile client's location: the movement cost and the locating cost. Past methods can only minimize one of the two costs, but not both. The major contribution of this paper is to present methods that minimize both costs simultaneously. Our performance analysis proves that the proposed methods are superior to the past ones.     

MODEC: A Multi-Granularity Mobile Object-Oriented Database Caching Mechanism, Prototype and Performance

An inherent limitation in mobile data access is due to the unreliable and low bandwidth wireless communication channel. Caching of useful database items from database server in local storage of mobile clients is effective in reducing data access latency and wireless bandwidth consumption. In the event of disconnection, cached data can also serve the purpose of partial query processing. In this paper, we present the implementation and evaluate a new caching mechanism for object-oriented database systems in a mobile environment called MODEC. MODEC possesses the capabilities of performing caching at multiple granularities and adapting to changes in data access pattern, providing improved performance through tolerating limited inconsistency to read-only transactions. This caching capabilities is supported via standard ODMG modeling constructs. The prototype of MODEC is implemented using ODE database. Empirical system performance results are obtained from experiments on the prototype with data from a real-life database. The results are validated against results obtained via detailed simulation studies on MODEC. Both sets of results are found to be consistent and are in favor of our MODEC mechanism in providing a feasible solution to the mobile data access problem under the constraints in a mobile environment.     

嵌入式移动数据库的客户机端Cache管理

嵌入式移动数据库是一个具有广阔应用前景的新兴技术,具有嵌入式系统和移动计算的应用特点,有许多关键技术亟待研究和解决。主要论述数据广播技术中客户机端Cache的管理,通过对移动数据库应用中Cache的替换策略、数据预取策略和数据一致性问题的讨论,探讨如何更好地减小客户机端访问请求的平均响应时间。     

移动自组网络组密钥管理框架

许多应用于军事、紧急救灾等场合的移动自组网络需要安全组通信支持,然而节点的移动性、链路不可靠以及多跳通信延迟等特点使移动自组网络的组密钥管理面临巨大的挑战。基于秘密共享机制和RSA非对称机密体制提出了一种新的移动自组网络组密钥管理框架DGKMF,该框架具有不依赖网络拓扑结构、组密钥局部生成以及有效维护组密钥的一致性的特点。模拟实验表明,DGKMF在组密钥更新成功率和延迟等方面均优于其他协议和算法。     

移动数据库技术及其在军事领域的应用研究

首先介绍了移动数据库和移动计算的基本原理,接着讨论了该技术在军事领域应用时应解决的关键技术,给出了军事应用的硬件性能、信息实时性及数据安全性等技术要求,最后归纳了该技术在军事领域的典型应用,并指出了该领域的一些热点和难点问题。     

A mobility-aware dynamic database caching scheme for wireless mobile computing and communications

This paper describes a mobility-aware dynamic database caching scheme for wireless mobile computing and communications. A mobile-floating agent scheme is proposed, in which caching techniques are cognizant of the mobile nature of mobile users and the location-sensitive nature of mobile systems. The mobile-floating agent maintains a second class cache in the fixed network and employs Barbara's invalidation reports broadcasting cache consistency strategies to maintain a dynamic cache consistent with the first class cache in the mobile client. The invalidation reports broadcasting scheme is combined with knowledge of the mobility behavior of each individual mobile user and broadcasts of invalidation reports only occur within the user's mobility area. The evaluation results show that, for a large system (200 cells), this scheme can reduce the system cost by more than 87%, for even highly mobile users, compared with a fully replicated database system.Recommended by: Daniel Barbara, Ravi Jain and Narayanan Krishnakumar     

一种基于移动代理的分布式入侵检测的体系结构

首先介绍了移动代理技术,并提出了一种基于移动代理的分布式入侵检测的体系结构,最后结合几种入侵的实例,来说明该体系结构的工作原理。     

A Framework for Management of Semistructured Probabilistic Data

This paper describes the theoretical framework and implementation of a database management system for storing and manipulating diverse probability distributions of discrete random variables with finite domains, and associated information. A formal Semistructured Probabilistic Object (SPO) data model and a Semistructured Probabilistic Query Algebra (SP-algebra) are proposed. The SP-algebra supports standard database queries as well as some specific to probabilities, such as conditionalization and marginalization. Thus, the Semistructured Probabilistic Database may be used as a backend to any application that involves the management of large quantities of probabilistic information, such as building stochastic models. The implementation uses XML encoding of SPOs to facilitate communication with diverse applications. The database management system has been implemented on top of a relational DBMS. The translation of SP-algebra queries into relational queries are discussed here, and the results of initial experiments evaluating the system are reported. Work performed while a Ph.D. student at the University of Kentucky.     

A Fast Parallel Clustering Algorithm for Large Spatial Databases

The clustering algorithm DBSCAN relies on a density-based notion of clusters and is designed to discover clusters of arbitrary shape as well as to distinguish noise. In this paper, we present PDBSCAN, a parallel version of this algorithm. We use the ‘shared-nothing’ architecture with multiple computers interconnected through a network. A fundamental component of a shared-nothing system is its distributed data structure. We introduce the dR*-tree, a distributed spatial index structure in which the data is spread among multiple computers and the indexes of the data are replicated on every computer. We implemented our method using a number of workstations connected via Ethernet (10 Mbit). A performance evaluation shows that PDBSCAN offers nearly linear speedup and has excellent scaleup and sizeup behavior.     

A Low-Cost Checkpointing Technique for Distributed Databases

For distributed databases, checkpointing is used to ensure an efficient way to perform global reconstruction. However, the need for global reconstruction is infrequent. Most current checkpointing approaches for distributed databases are too expensive during run time. Some of them allow the checkpointing process to run in parallel with normal transactions at the cost of more data and resource contention, which in turn causes longer response time for normal transactions. Thus, an efficient way to checkpoint distributed databases is needed to avoid degrading the system performance. This paper presents a low-cost solution, called Loosely Synchronized Local Fuzzy Checkpointing (LSLFC), to these problems. LSLFC supports global reconstruction, and our performance study shows that LSLFC has little overhead during run time.     

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。     

基于用户查询日志的双级缓存结构设计

文章针对目前分布式缓存系统命中率低和查询处理时间长的问题,在分析某中文搜索引擎于2009年9月查询日志集的用户查询特征和热点内容分布特征的基础上,设计并实现了包括静态缓存和动态缓存的双级缓存结构。最后,从理论分析和实验数据两方面,论证了基于查询日志的双级缓存结构在性能方面更具优越性。     

移动客户机中缓存技术的应用研究

在移动计算环境中,移动性和断接性是它的最主要的两个特点.为了支持断接操作,数据时常需要先存储到移动客户机中.缓存技术成为移动计算环境中的重要技术.本文研究了基于广播技术中客户机端缓存的管理技术,讨论了缓存管理的粒度问题、缓存一致性策略和缓存替换策略三个关键问题.     

移动应用集成:框架、技术与挑战

随着移动互联网的广泛普及和飞速发展,出现了大量的移动应用,其种类和数量还在不断增加.手机制造商、电信运营商和互联网服务提供商等纷纷推出自己的移动应用商店,移动应用已经成为互联网发展的一种新模式.移动应用的相关信息分布在应用商店、专业论坛及社交网络中,由于其信息的多样性、异构性、动态性,给移动应用集成带来了巨大挑战.移动应用集成的主要任务是研究如何把海量的移动应用及其相关信息有效地集成起来,为用户提供高质量的搜索、发现和推荐服务.移动应用集成还是一个比较新的研究领域,文中提出了一个移动应用集成的基本框架,对移动应用集成中的关键技术进行了分析总结,在此基础上对未来的研究方向及挑战进行了阐述.     

移动数据库关键技术研究

文章介绍了移动数据库的概念、体系结构,阐述了移动数据库的特点,详细分析了移动数据库的复制与缓存、移动事务、数据广播等关键技术.     

移动数据库关键技术研究

文章介绍了移动数据库的概念、体系结构，阐述了移动数据库的特点，详细分析了移动数据库的复制与缓存、移动事务、数据广播等关键技术：     

面向移动终端的图片动态适配系统的设计与实现

本文设计并实现了一个面向移动终端的图片动态适配系统。该系统基于动态适配技术,提供针对移动终端的图片适配业务,能够通过配置文件对图片质量、图片尺寸、图片格式、图片特性(动画、透明背景等)进行灵活的适配控制,使用缓存机制缩短适配时间提高系统性能,并且可以通过分布式部署增加图片适配业务量。经过测试,该图片动态适配系统在通用性、系统性能和适配效果上均表现良好。