移动计算环境下的同步模型研究

结合缓存技术和移动数据库技术,在现有的同步模型的基础上,提出了一个改进的同步模型--基于Web内容和数据集同步的同步复制模型,满足了移动计算的要求.客户端缓存部分数据和网页,允许在网络断连的情况下仍可以在客户端操作,通过同步模型的同步,保持客户端与服务器之间的数据的一致性.     

基于操作日志的完井数据同步模型

同步技术是提高移动数据库系统性能的一项关键技术。依托完井移动平台,结合完井业务数据,提出一种基于操作日志的移动数据同步处理模型,重点分析了该模型中的日志序列的生成以及冲突的消解,并给出了具体的实现算法。该模型允许移动终端在断接状态下对本地副本数据进行操作,并通过移动事务日志记录用户行为,当重新连接时,根据服务器返回的日志序列进行同步处理,使系统最终收敛于一致性状态。同时还引入了日志合并、时间戳等方法,有效减少了移动终端的资源消耗,提高了同步效率。实验表明该算法能快速高效地完成客户端与服务器之间的数据更新与交互。     

移动数据库缓存模型研究

针对移动数据库系统性能有待提高的问题,提出了一种移动数据库缓存模型。采用基于消息摘要的同步算法,通过比较移动客户端与服务器消息摘要表中的消息摘要值,完成缓存同步,维护移动客户端缓存与服务器数据的一致性;该模型还考虑了数据的时效性与事务的优先级,设计了一种基于价值函数的缓存替换算法。实验结果表明,随着缓存数据个数的增加,所提算法的缓存命中率高于最近最少使用(LRU)和LA2U算法,同时随着访问频率的增加,事务的重启率低于LRU和LA2U,有效提高了移动数据库缓存的性能。     

移动数据库管理系统客户端MDM2Lite的设计与开发

MDM2是在DM3基础上设计的一个移动数据库原型系统。它针对移动计算的特点设计了客户端DBMS,并提出虚拟服务器的概念。文章主要讨论了MDM2客户端DBMSMDM2Lite如何有效地支持移动环境下的断接操作、数据同步以及和移动相关的操作,最后通过一个具体实例描述了其主要工作流程。     

移动数据库系统乐观事务处理策略

在移动数据库系统中，计算平台的移动性，频繁的断接性以及长事务等特性使得传统的事务处理模式不再适用，为了解决移动数据中的事处处理问题，提出了一种新的移动事务处理模型－乐观两阶段提交移动事务模型（O2PC－MT），该模型采用乐观并发控制与两阶段提交协议相结合的方法，对移动事务的长事务特性提供了灵活与有效的支持，此外，该模型允许移动计算机分多发送中务操作，且在事务执行过程中可以任意移动，从而提供了对交互式事务及随意移动性的支持，实验结果表明，与基于两段锁协议及其变形的其它移动事务处理模型相比，O2PC－MT提高了系统的事务吞吐率并改善了系统的总体性能。     

移动数据库中数据复制同步处理策略的研究

同步技术是保证复制移动数据库系统一致性的一项关键技术,鉴于目前移动复制同步技术存在通讯数据量大,存储空间消耗多,尤其是在网络带宽下降时,不能及时更新客户端的数据,导致移动事务执行失败等缺陷。通过UTLRSP（Union Transaction-Level Result-Set Propagation,关联事务结果集）复制同步模型结合数据广播技术,并利用基于优先级的增量更新算法实现客户端与中心数据库服务器的数据同步处理。实验结果表明,与两级复制机制相比,UTLRSP模型将事务作相关联处理,且只保存事务结果,有效降低了存贮空间的消耗,减小了同步过程中通讯数据量;基于优先级的增量更新算法根据数据新鲜度排列优先级,保证在无线网络带宽下降时新鲜度最高的数据先传输,提高了数据的传输效率、动态新鲜度以及客户端的可扩展性。     

气象移动办公系统应用研究

随着信息科技的发展,移动办公技术可以使用户把现有的计算机办公应用借助互联网和无线网络扩展到手机、PDA或其他智能终端上。该文针对气象部门工作需求,建立了气象移动办公系统。实现公文管理、企业通讯录管理、配置管理、监控管理、权限管理等模块在移动客户端上的相应操作,为人员提供了移动信息化服务。     

气象移动办公系统应用研究

随着信息科技的发展,移动办公技术可以使用户把现有的计算机办公应用借助互联网和无线网络扩展到手机、PDA或其他智能终端上。该文针对气象部门工作需求,建立了气象移动办公系统。实现公文管理、企业通讯录管理、配置管理、监控管理、权限管理等模块在移动客户端上的相应操作,为人员提供了移动信息化服务。     

无线移动环境中基于移动Agent的实时构件组装机制研究

由于无线网络较窄、昂贵的带宽，及移动设备自身有限的硬件能力，在无线移动环境中进行实时构件组装调用时面临着更多的技术挑战，需要一种高效、可靠的机制给予支持。本文提出一种基于移动Agent的无线网络环境构件组装调用机制。该机制利用移动Agent作为移动客户端与构件服务器之间交互的中介，提供了灵活、可配置的组装结构，从而有效避免移动客户端不必要的访问操作，节省了移动客户端的无线网络连接开销，与其他机制相比有着较高的执行效率；同时该机制可有效支持移动客户端发生故障后的状态恢复，从而确保运行过程的可靠性。最后本文通过实验分析了MAWA机制的可靠性与高效性。     

基于Web Service的车险移动查勘系统

随着移动通信技术的高速发展以及移动通信设备的普及,各种移动应用系统应运而生,给人们的工作、生活带来了极大的方便.实现基于Web Service的车险移动查勘系统,该系统基于Android系统,采用3G通信技术.以Web Service处理车险业务.客户端使用JSR172调用Web Service来传递车险数据,从而实现移动客户端和服务器端的通信.系统有良好的交互界面,操作简单、方便,不仅能提高查勘效率和理赔服务质量,还可以进一步拓展其它业务.     

基于移动数据库的事务处理模型的研究

对移动数据库的关键技术之一事务处理进行了分析与探讨。在分析现有移动事务处理模型的基础上，结合研究开发的嵌入式移动数据库系统SwiftDB，提出增加接入代理层的事务处理系统结构，并根据移动计算环境的特点和具体应用需求，分析了移动节点上事务状态，改进两级复制模型的移动事务解决方案。     

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.     

Utilizing national public-key infrastructure in mobile payment systems

Payments are the locomotive behind any business domain. It has been predicted that mobile payments will become one of the most successful mobile services, and the security of payments is an important requirement. However, it is difficult to strongly authenticate mobile users remotely and provide an adequate level of non-repudiation of transactions. In this article, we argue that a nationwide public-key infrastructure supported by governmental bodies can be used in a mobile payment system. Not only does it provide strong security, but it also makes the system open to any mobile user, merchant, or financial service provider. Two payment protocols are described: one for virtual point-of-sale payments, and one for vending machine payments. We argue that such a system can be implemented using open development platforms, and its performance is adequate for enabling swift transactions. A prototype of a system which accepts virtual point-of-sale payments is implemented, and its performance and usability are evaluated.     

移动数据库广播的并发控制算法研究

在基于数据广播的移动信息服务中,由于更新数据和广播数据两个过程是并发执行的,所以移动客户将面临接收数据不一致性问题。为此,该文提出了一种基于规则的并发控制算法来解决以上问题。在允许同步更新的情况下采用事件-条件-操作规则来进行无冲突的数据广播。该算法对移动机和数据库服务器的影响很小,同时又为基于广播的移动计算提供了数据一致性服务。     

An economics-based negotiation scheme among mobile devices in mobile grid

In this paper, we propose an economics-based distributed negotiation scheme among mobile devices in mobile grid. In our model, there are energy negotiation and transactions between buyer devices and seller devices. Dynamic allocation of energy resources in mobile grid is performed through online transactions within markets. Mobile devices can be sellers and buyers that use optimization algorithms to maximize predefined utility functions during their transactions. Seller device agents sell the underlying energy resources of the mobile device. Buyer device agent makes buying decisions within the budget constraints to acquire energy resources. An economics-based negotiation algorithm among mobile devices is proposed. The proposed algorithm decomposes mobile grid system optimization problem into a sequence of two sub-problems. In the simulation, the performance evaluation of economics-based negotiation algorithm is evaluated.     

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.     

基于移动AGENT系统的网络分布式数据访问

给出了一个访问网络数据库的移动Agent的系统,该系统建立在ECP协议和移动Agent基础上,用纯JAVA代码实现,利用ECP在提高通信效率的情况下访问网络分布式数据库。     

无线数据广播中动静结合分片段移动实时事务模型

无线广播环境非对称通信等的诸多限制以及数据访问者的移动性及实时性等需求,使平坦事务模型及现有移动事务模型都无法满足无线数据广播中移动实时事务处理的要求。从无线数据广播环境特点出发,针对移动应用需求特征,提出了一种动静结合分片段移动实时事务模型。     

基于移动AGENT系统的网络分布式数据访问

给出了一个访问网络数据库的移动Agent的系统,该系统建立在ECP协议和移动Agent基础上,用纯JAVA代码实现,利用ECP在提高通信效率的情况下访问网络分布式数据库。     

支持断接的移动实时事务调度

在移动计算环境中,事务移动性和频繁断接使得传统实时事务调度机制不足以支持移动实时事务的执行。该文给出了一个支持无线网络频繁断接的软实时事务调度协议SSRTD。该协议是基于事务具有扩展截止期和结果相似性进行设计的,并可根据移动主机的连接状况决定事务执行结果的发送时间。通过性能测试,表明所提出的调度策略能提高移动实时事务的成功率。