移动数据库技术研究

当前无线网络的飞速发展带动了移动数据库的发展,移动数据库和传统的固定数据库的区别在于其断接性和动态性,移动终端设备在各个无线节点的频繁切换也给移动数据库的事务处理带来一定的困难,目前移动数据库支持事务在服务器和客户端双向处理的机制。文章具体研究了移动数据库技术。     

移动实时数据库的时间一致性研究

在实际应用中,实时的移动数据库系统不仅需要确保事务完成的最后期限,而且还需保证事务处理的时态一致性,为此研究了移动实时数据库的时间一致性.从移动实时数据库时间特性的定义出发,分析实时事务的时间一致性限制因素,提出实时事务的时间一致性维护策略.性能测试结果表明,乐观协议OPT-Wait与基于锁的协议VL-HP各有优劣,在延误截止时间率方面,OPT-Wait协议比VL-HP协议性能好.     

基于大数据量的电商鲜花系统设计与实现

为了解决传统花店经营销售存在的区域性与时效性等问题,将互联网技术运用于传统花店经营销售模式中,该系统采用客户/服务器结构,客户端需要通过介质多样的广域网与服务端通讯,主要解决由于网络的不可靠性,常常出现的传输过程中交易数据的丢失,造成客户端与服务端的交易不完整或数据不一致,导致商家的资金风险和信誉问题.通过数据库主从模式给数据加锁的方式,保证了数据库事务的一致性和数据库准确性问题.     

无线分布式系统中基于移动Agent的日志分析

在分布式系统中,利用移动Agent主动读取和分析各结点的数据库事务日志,并与其他结点的移动Agent相互协作,共同完成数据的校验和检测,从而实现整个系统数据的一致性、完整性,利用该方法实现了多结点无线分布式系统中SQL Server2000数据库数据的一致性存储,并在工程实践中取得了满意的效果。     

确保时态一致性的实时并发控制协议

实时控制系统通常需要维护大量的时态数据对象,这些时态数据对象是现实世界不断变化的物理环境的逻辑表示.应用事务通过对时态数据对象的访问来产生最终的控制活动.在实际应用中,实时控制系统不仅需要确保事务能在规定的期限内完成,也需要保证事务存取的是时态一致性的数据对象.传统的实时并发控制协议强调事务截止期的满足,而忽略了事务对其所存取数据对象有时态一致性需求.本文首先给出了数据和事务时态一致性的形式化定义,在此基础上,提出了一种新的能确保时态一致性的实时并发控制协议:时态一致性高优先级两段锁协议(TCHP-2PL).为了实现更好的实时性能,我们对TCHP-2PL进行了改进,通过引入相似性概念,提出了TCHP-2PL的改进版本:STCHP-2PL.性能测试结果显示,STCHP-2PL在确保时态一致性的同时仍能保证很好的实时性能.     

一种基于移动计算环境的并发控制策略

针对移动计算环境中传统的并发控制机制并不足以支持移动事务执行的问题,提出一种新的事务管理机制以提高移动事务的处理效率.文中着重研究移动事务的并发控制机制,提出了一种基于动态计时器机制的并发控制策略.该策略主要是在锁管理器中添加动态计时器,通过调整事务执行队列以及动态的分配事务执行时间,达到减少事务的重启次数,提高事务提交率的目的.性能测试表明,所提出的并发控制策略能提高移动计算环境下事务的成功率.     

简讯

赛门铁克启动新客户端策略。2003年12月9日,赛门铁克启动了新客户端策略一致性计划,促进远程和移动客户端安全策略的执行。另外,公司和思科正在开展一项协作计划,将其安全解决方案和思科的入网控制计划联合起来,全力控制病毒和蠕虫等造成的破坏。     

基于IIPP和移动Agent的冗余数据一致性的研究与实现

冗余技术在提高数据可靠性和可用性方面发挥了重要作用,随之而来的数据一致性问题成为研究热点。提出一个基于IIPP和移动Agent的一致模型,在IIPP思想的指导下,应用Agent具有移动特性和处理任务的特性来进行事务的发送、转换及分发等操作,从而实现数据的弱一致性。该模型在实际应用中得到了很好的验证,提高了系统的智能性、高效性及自适应性。     

分布式移动代理系统的事务管理及死锁检测研究

讨论了并发执行的移动代理间的一致性控制问题,给出了移动代理的形式模型及其交互执行的正确性准则,然后基于上述模型,提出了一种有效的分布式死锁检测算法,该算法具有独立于网络的拓扑结构,死锁的检测和事务代理的执行异步操作,不对代理的移动性施加任何限制等特点。     

单线图在移动GIS的沿布

通过获取单线图数据文件,在移动端解析沿布的方式,实现单线图在移动GIS上的快速动态沿布;移动端保留时间段内的文件数据和实现本地化的图形操作,减少移动端对移动网络的过多依赖,减轻服务器的计算压力同时提升客户端的响应速度;依据实际需要逐条显示单线图,提升单线图在客户端的显示质量,提高客户的满意度。     

面向移动计算环境的混合式数据同步机制

提出混合式数据同步机制,有机融合集中式和ad hoc架构,设置自组织域(SOD, self-organization domain),减少了同步数据通信量和数据同步服务器负载;提出基于节点能力值的数据分发策略,根据移动终端综合处理能力值来建立SOD树分发路径,实现同步数据的高效分发;还提出了基于轨迹变更的增量捕获策略,采用触发器捕获操作日志,用净化方法合并操作日志得到净增量数据。实验结果表明,混合式数据同步机制能更好地维护移动计算环境中数据的一致性,缩短同步响应时间,减少同步数据通信量,降低同步服务器负载。     

Adaptation Mechanisms for Transactions in Mobile Computing Environments

Advances in wireless communication technologies and portable computers have turned mobile computing into a reality. These environments are characterized by a high dynamism that can hamper the execution of applications. This paper presents a set of adaptation mechanisms that can be used within a transaction context to overcome the high dynamism and resource restrictions of the mobile environment. Three adaptation mechanisms were proposed: isolation level, operation mode and transaction mobility.     

Mobile Payment Based on Transaction Certificate Using Cloud Self‐Proxy Server

Recently, mobile phones have been recognized as the most convenient type of mobile payment device. However, they have some security problems; therefore, mobile devices cannot be used for unauthorized transactions using anonymous data by unauthenticated users in a cloud environment. This paper suggests a mobile payment system that uses a certificate mode in which a user receives a paperless receipt of a product purchase in a cloud environment. To address mobile payment system security, we propose the transaction certificate mode (TCM), which supports mutual authentication and key management for transaction parties. TCM provides a software token, the transaction certificate token (TCT), which interacts with a cloud self‐proxy server (CSPS). The CSPS shares key management with the TCT and provides simple data authentication without complex encryption. The proposed self‐creating protocol supports TCM, which can interactively communicate with the transaction parties without accessing a user's personal information. Therefore, the system can support verification for anonymous data and transaction parties and provides user‐based mobile payments with a paperless receipt.     

一种基于GPRS网络的缓存一致性策略

提出了在GPRS网络中加入一个验证服务器VS维护无线移动环境下的缓存一致性的策略,利用GPRS骨干网中SGSN的有关移动终端的位置信息和用户访问的局域性,有针对性地只向在线终端发送所缓存数据的失效信息,有效地降低异步传输中的信息量。性能分析表明,该策略简化了维护缓存一致性的复杂性,使用很少的移动终端计算量,支持任意断开连接时间和一个PLMN网内的漫游。     

Survey on the causal consistency of data

Causal consistency is one of the important projects to ensure data consistency in distributed storage.The current research focuses on causal consistency including optimization of clock method,design of the protocol and the optimization of operation transaction sequence.In the actual cloud environment,in addition to clock skew and query amplification,there are also insecure factors such as Trojans and untrusted third parties,which will destroy the causal consistency metadata stored by users,and the consistency of user’s operating results,even affect the availability of the storage environment.From the perspective of performance improvement and security in distributed storage,the clock synchronization,data replications,analysis and design of server protocol,related research progress of the serialization of operational affairs were introduced combined with consensus mechanisms such as blockchain.At the same time,their principlest,advantages,limitations,and different utilities in terms of security constraints were discussed,and then the future development trends and follow-up research directions were point out at last,which would provide a reference and help for the research in this field.     

基于代理的移动数据库研究

近年来,无线技术的发展促进了移动计算的研究,但是多数移动数据库系统使用传统的客户机/服务器模式或单代理模式处理移动查询,进而产生了数据大量迁移的问题。文章提出了一种基于多移动代理技术的移动数据库查询处理模型,旨在减少处理过程中的数据迁移量,提高移动环境下查询分布式异构数据库的性能。     

Design and performance studies of an adaptive cache retrieval scheme in a mobile computing environment

In a mobile computing system, as users move to a new service area, the new server is usually considered to take over the execution of running programs for mobile users from the previous server so as to reduce the communication overhead of a mobile system. This procedure is referred to as service handoff. Note that when service handoff occurs, the new server will lose its advantage for cache access. To remedy this, we explore in this paper several cache retrieval schemes to improve the efficiency of cache retrieval. In particular, we analyze the impact of using a coordinator buffer to improve the overall performance of cache retrieval. Moreover, in light of the properties of transactions (i.e., temporal locality of data access among transactions), we devise a Dynamic and Adaptive cache Retrieval scheme (DAR) that can utilize proper cache methods according to some specific criteria to deal with the service handoff situation in a mobile computing environment. Performance of these cache retrieval schemes is analyzed and a system simulator is developed to validate our results. We devise a systematic procedure for determining the optimal operating points of DAR. Our experimental results show that by adaptively adopting the advantages of different cache retrieval methods, DAR significantly outperforms other schemes and is particularly effective for a mobile computing environment.     

一种基于虚拟应用的安全防泄漏系统

针对目前日益严重的信息资产泄露问题,在对比已有的信息泄露的防御技术基础上,提出一种＂基于虚拟应用的安全防泄漏系统＂,通过集中运算、虚拟应用技术,在服务器上为每一个用户的应用构建独立的计算环境;采用远程桌面、SSLVPN技术保证集中计算环境中数据与用户操作终端的安全隔离;同时基于信息在服务器集中存储和运算,实现终端无痕（用户终端没有数据计算痕迹）,防止数据在应用过程中泄露;最后采用统一认证和应用授权发布,管理用户对数据的访问和输出控制。     

An efficient algorithm for dynamic task offloading using cloudlets in mobile cloud computing

It is a visible fact that the growth of mobile devices is enormous. More computations are required to be carried out for various applications in these mobile devices. But the drawback of the mobile devices is less computation power and low available energy. The mobile cloud computing helps in resolving these issues by integrating the mobile devices with cloud technology. Again, the issue is increased in the latency as the task and data to be offloaded to the cloud environment uses WAN. Hence, to decrease the latency, this paper proposes cloudlet‐based dynamic task offloading (CDTO) algorithm where the task can be executed in device environment, cloudlet environment, cloud server environment, and integrated environment. The proposed algorithm, CDTO, is tested in terms of energy consumption and completion time.