基于GPRS网络的强一致性两级缓存系统框架

无线移动环境中缓存的主要目的是减少对无线带宽资源的占用和节省电池能量,然而移动无线终端的漫游与经常断开连接又给缓存内容的一致性带来了一系列新的问题。本文针对目前运行的GPRS网络,提出了在用户端（移动终端）和GPRS骨干网中添加验证服务器VS（Validation Server）对数据进行两级缓存的系统框架和缓存强一致性策略。该框架简化了无线移动环境下维护缓存一致性的复杂性,有效地降低了对无线带宽的占用和数据库服务器的负载,支持移动终端断开连接的时间任意和在一个公众陆地移动通信网PLMN网内的漫游,具有很强的实用性。     

移动数据库中缓存技术的比较研究

缓存技术是提高数据访问性能的经典技术,已经在计算技术的很多方面得到了成功的应用。在移动计算环境中,由于设备和网络资源的限制,使得缓存技术的应用在移动数据库中显得非常重要。缓存技术的引入能有效减少带宽需求,降低通信成本以及节省移动计算机的能耗。然而,如何有效进行缓存维护从而确保一致性,一直是国内外研究的热点和难点。本文正是针对这一问题,对缓存一致性维护的各种研究方法的现状进行了深入剖析和探讨。     

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。     

移动环境下缓存弱一致性的研究

在移动环境下，客户缓存为提高客户一服务器数据库系统的整体性能提供了有效途径。缓存与服务方数据的同步策略是缓存研究的重要内容。移动环境下，考虑到网络的带宽、开销和可靠性等因素，客户有可能允许缓存维护弱一致性，即允许缓存与服务方数据存在偏差。本文针对基于语义的缓存，给出客户限定偏差范围的方法，并且提出基于有效期的缓存同步算法。     

稀疏机会网络中基于固定中继节点与消息相关性的缓存管理策略

针对稀疏机会网络中固定中继节点和移动节点间的相遇频率以及缓存资源的差异性问题,在多副本路由协议中,提出一种结合固定中继节点重要性和消息相关性的缓存管理策略。该策略通过交互固定节点和移动节点的接触信息和消息队列信息,减少固定中继节点缓存中冗余消息的数量,从而合理地利用固定中继节点的缓存资源。仿真结果表明,所提的缓存管理策略能够在保证消息传输成功率的基础上提高固定中继节点缓存空间的利用率。     

缓存技术在移动数据库中的应用研究

缓存技术是提高教据访问性能的经典技术,已经在计算技术的很多方面得到了成功的应用.在移动计算环境中,由于设备和网络资源的限制,缓存将发挥更加重要的作用.研究了移动数据库中的客户端缓存管理技术,重点讨论了缓存管理的缓存粒度、缓存一致性策略和缓存替换策略3个关键问题.     

基于P2P的3G流媒体代理缓存策略

3G时代已经到来,伴随着3G的快速发展,移动流媒体服务的需求迅速增长。由于移动网络带宽远达不到互联网的带宽,流媒体业务的增长将增加网络延迟,影响流媒体的观看质量,因此提出了一种新的基于P2P的3G流媒体缓存代理结构PSPA,配合PSPA设计了代理缓存置换策略SCOP,该设计能有效降低对移动核心网带宽的占用。最后,仿真实验和实验结果分析表明,PSPA体系与代理缓存置换策略SCOP的结合,能有效提高移动流媒体的服务质量,对3G流媒体的应用具有一定的参考价值。     

移动数据库中基于数据广播缓存一致性的研究

随着移动设备的普及以及移动基础设施的迅速发展,移动计算环境日益成熟。数据广播技术作为移动环境中的重要技术得到广泛的研究,本文着重的介绍了数据广播中缓存一致性的相关问题以及各种广播技术解决缓存一致性的特点。     

基于Oracle DCN的缓存一致性技术

针对J2EE多层架构应用中的缓存一致性问题,提出一个利用Oracle数据库更改通知(DCN)机制维护缓存一致性的方案,以分销资源计划系统为例,在中间层通过应用Java缓存系统来存储系统中频繁存取的数据库结果集,在数据层利用DCN机制维护缓存一致性,论述了相关实现技术。应用结果表明,该方案是有效和可行的。     

无线网络环境下的缓存策略研究

日益普及的无线网络和移动设备为普适的Internet接入提供了良好的硬件基础,缓存技术是普适Internet场景中人们进行信息共享和分发的关键技术之一.综述了两类无线网络环境,即基于基础设施无线网络环境和移动自组网中的缓存策略,具体包括缓存放置策略、缓存替换策略、缓存一致性维护算法.进而分析、讨论了上述策略的优缺点,并指出了缓存策略的发展趋势.     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

View-based model-driven architecture for enhancing maintainability of data access services

In modern service-oriented architectures, database access is done by a special type of services, the so-called data access services (DAS). Though, particularly in data-intensive applications, using and developing DAS are very common today, the link between the DAS and their implementation, e.g. a layer of data access objects (DAOs) encapsulating the database queries, still is not sufficiently elaborated, yet. As a result, as the number of DAS grows, finding the desired DAS for reuse and/or associated documentation can become an impossible task. In this paper we focus on bridging this gap between the DAS and their implementation by presenting a view-based, model-driven data access architecture (VMDA) managing models of the DAS, DAOs and database queries in a queryable manner. Our models support tailored views of different stakeholders and are scalable with all types of DAS implementations. In this paper we show that our view-based and model driven architecture approach can enhance software development productivity and maintainability by improving DAS documentation. Moreover, our VMDA opens a wide range of applications such as evaluating DAS usage for DAS performance optimization. Furthermore, we provide tool support and illustrate the applicability of our VMDA in a large-scale case study. Finally, we quantitatively prove that our approach performs with acceptable response times.     

A pragmatic multi-method investigation of discrepant technological events: Coping,attributions, and ‘accidental’ learning

Discrepant technological events or situations that entail a problem, a misunderstanding or a difficulty with the Information Technology (IT) being employed, are common in the workplace, and can lead to frustration and avoidance behaviors. Little is known, however, about how individuals cope with these events. This paper examines these events by using a multi-method pragmatic approach informed by coping theory. The results of two studies – a critical incident study and an experiment – serve to build and test, respectively, a theoretical model that posits that individuals use a variety of strategies when dealing with these events: they experience negative emotions, make external attributions, and adopt engagement coping strategies directed at solving the event, eventually switching to a disengagement coping strategy when they feel they have no control over the situation. Furthermore, users’ efforts may result in ‘accidental’ learning as they try to overcome the discrepant IT events through engagement coping. The paper ends with a discussion of the results in light of existing literature, future opportunities for research, and implications for practice.     

The Distributed Time-Triggered Simulation Scheme: Core Principles and Supporting Execution Engine

Distributed real-time simulation is a young technology field but its practice is under increasing demands. In recent years the author and his collaborators have been establishing a new approach called the distributed time-triggered simulation (DTS) scheme which is conceptually simple and easy to use but widely applicable. The concept was initiated in the course of developing a new-generation object-oriented real-time programming scheme called the time-triggered message-triggered object (TMO) programming scheme. Some fundamental issues inherent in distributed real-time simulation that were learned during recent experimental studies are discussed along with some approaches for resolving the issues. An execution engine developed to support both the TMOs engaged in control computation and the TMOs engaged in DTS is also discussed along with its possible extensions that will enable significantly larger-scale DTSs.     

Software-Konfigurationsmanagement in großen Softwareprojekten

Zusammenfassung Mit zunehmender Größe der Softwaresysteme verschärfen sich die für die Software-Herstellung typischen Probleme: Beherrschen großer Objektmengen, Erhalten der Systemkonsistenz, Kontrolle der ständigen Änderungseinflüsse und Gewährleisten einer langen Lebensdauer. Die Disziplin Konfigurationsmanagement bildet den methodischen Ansatz, diese Probleme besser zu beherrschen. Software-Konfigurationsmanagement faßt die Herstellung von Softwaresystemen als eine Abfolge von kontrollierten Änderungen an gesicherten Zwischen- und Endergebnissen auf. Dargestellt werden die Objekte und Funktionen des Software-Konfigurationsmanagements sowie die hierfür in großen Software-Projekten benötigten Methoden, Instanzen und Hilfsmittel.     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and     

Editorial:Brain-machine interface(BMI) and cyborg intelligence

正Brain-machine interfaces(BMIs)aim at building a direct communication pathway between the brain and an external device,and represent an area of research where significant progress has been made during the past decade.Based on BMIs,mind information can be read out by neural signals to control     

Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate     

SCIENCE CHINA Information Sciences SUBJECT INDEX TO VOLUME 57(2014)

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Information for Authors

正http://www.zju.edu.cn/jzus http://www.springerlink.com Aim The Journals of Zhejiang University-SCIENCE(A/B/C)are edited by the international board of distinguished Chinese and foreign scientists,and are aimed to present the latest developments and achievements in scientific research in China and overseas to the world’s scientific circles,especially to stimulate