面向对象数据库技术及其前景分析

面向对象数据库作为第三代数据库具有前两代数据库无法比拟的优点,满足复杂数据结构和海量存储需要,是新型数据库如多媒体数据库、空间数据库、演绎数据库、工程数据库实现的基础。具体分析了面向对象数据库技术的基本特征、优势、存在的问题,并对面向对象数据库技术未来前景做了预测。     

基于OCI和ODBC异构数据库通用接口设计

文中分析了ODBC和OCI数据库接口的特点,为解决异构数据库的共享,提出了一种数据库应用程序连接数据库的方法———通用数据库接口。首先明确了通用数据库接口模块在系统中的位置,接着分析了该接口模块具备的具体功能,介绍了模块设计中的三个层次,然后总结了该接口模块的优点。封装了ODBC和OCI的通用数据库接口,可以实现异构数据库的互连,同时可以提高系统的性能。通过数据库调用函数来实现对异构数据库的操作,该通用数据库接口具有通用、简单、可扩展、可优化等特点。     

组态软件中的历史数据处理过程

实时数据库中历史数据是系统定时从实时数据库中采样,保存到历史数据库中的数据,用户需要时可随时从历史数据库中访问历史数据。历史数据库包含内存历史数据库和磁盘历史数据库。内存历史数据库关注的是测点近期数据的组织方式;磁盘历史数据库管理的对象是历史数据文件和管理信息文件。本文描述了磁盘历史数据库的文件结构、缓冲区进行了描述,并阐述了磁盘历史数据库的实现技术。     

基于SQL Server数据库完整性约束的几点探讨

数据库的完整性约束是设计数据库的核心内容,一个数据库的完整性约束设计的好坏,直接影响到这个数据库的性能,同时也会影响数据库的开发,因此一个好的数据库需要严格考虑其完整性约束。本文对SQL Server 2000数据库中的完整性约束进行了探讨,并用T-SQL语句对数据库完整性约束进行了设计,从而实现了在数据库中存储数据的完整性、正确性和一致性。     

基于OCI和ODBC异构数据库通用接口设计

文中分析了ODBC和OCI数据库接口的特点．为解决异构数据库的共享，提出了一种数据库应用程序连接数据库的方法——通用数据库接口。首先明确了通用数据库接口模块在系统中的位置，接着分析了该接口模块具备的具体功能，介绍了模块设计中的三个层次，然后总结了该接口模块的优点。封装了0DBC和OCI的通用数据库接口．可以实现异构数据库的互连，同时可以提高系统的性能。通过数据库调用函数来实现对异构数据库的操作，该通用数据库接口具有通用、简单、可扩展、可优化等特点。     

面向企业网数据库信息的安全技术研究

从数据库信息安全的防护角度对面向企业网络的数据库信息安全展开了分析讨论,简单介绍了常见数据库安全措施和数据库信息安全的关键问题,重点提出了企业网数据库信息的加密改进思想。对数据库加密平台的实现展开了讨论,从加密模型框架和加密字典的设计两个角度完成了面向企业网数据库的信息安全设计。     

关于Access数据库安全性研究

数据库安全性问题是一直是围绕着数据库管理的重要问题,数据库数据的丢失以及数据库被非法用户的侵入使得数据库安全性的研究尤为重要。本文以比较常用的Access数据库为例围绕数据库的安全性技术作了分析,并介绍了数据库安全策略。     

与数据库结构无关的数据库备份存储研究

针对传统的数据库备份,数据库的备份与源数据库的结构特征紧密相关,备份中心存储资源严重浪费的现状,提出了一种与数据库结构无关的数据库备份的存储方法。通过数据封装、多级索引等技术在备份中心实现数据库备份数据的存放形式与源数据库的数据结构无关,实现了不同种类数据库的备份数据共享一个存储平台。实验结果表明,该方法不仅能实现不同种类数据库共享存储,而且有效地提高了系统资源的使用效率。     

ADO数据库访问技术在脚本语言中的应用

介绍了ADO数据库技术的原理,对在不同数据库、不同脚本语言下利用ADO数据库技术访问数据库进行了探讨。     

Delphi应用程序中如何使用事务进行数据更新

数据库事务处理是数据库应用开发中的常见问题。了解和掌握数据库事务对于数据库应用系统设计者来说相当重要。本文首先数据库事务做了简单描述,并详细介绍了Delphi中用于实现数据库事务的TDataBase构件的重要属性和方法。     

Affinity-Based Network Interfaces for Efficient Communication on Multicore Architectures

Improving the network interface performance is needed by the demand of applications with high communication requirements (for example, some multimedia, real-time, and high-performance computing applications), and the availability of network links providing multiple gigabits per second bandwidths that could require many processor cycles for communication tasks. Multicore architectures, the current trend in the microprocessor development to cope with the difficulties to further increase clock frequencies and microarchitecture efficiencies, provide new opportunities to exploit the parallelism available in the nodes for designing efficient communication architectures. Nevertheless, although present OS network stacks include multiple threads that make it possible to execute network tasks concurrently in the kernel, the implementations of packet-based or connection-based parallelism are not trivial as they have to take into account issues related with the cost of synchronization in the access to shared resources and the efficient use of caches. Therefore, a common trend in many recent researches on this topic is to assign network interrupts and the corresponding protocol and network application processing to the same core, as with this affinity scheduling it would be possible to reduce the contention for shared resources and the cache misses. In this paper we propose and analyze several configurations to distribute the network interface among the different cores available in the server. These alternatives have been devised according to the affinity of the corresponding communication tasks with the location (proximity to the memories where the different data structures are stored) and characteristics of the processing core. As this approach uses several cores to accelerate the communication path of a given connection, it can be seen as complementary to those that consider several cores to simultaneously process packets belonging to either the same or different connections. Message passing interface (MPI) workloads and dynamic web servers have been considered as applications to evaluate and compare the communication performance of these alternatives. In our experiments, performed by full-system simulation, improvements of up to 35% in the throughput and up to 23% in the latency have been observed in MPI workloads, and up to 100% in the throughput, up to 500% in the response time, and up to 82% in the requests attended per second have been measured in dynamic web servers.     

Spatio-temporal distribution of rice phenology and cropping systems in the Mekong Delta with special reference to the seasonal water flow of the Mekong and Bassac rivers

Multi-temporal Moderate Resolution Imaging Spectroradiometer (MODIS) data was used to estimate the spatial distribution of heading date and rice-cropping system employed in the Mekong Delta relative to seasonal changes in water resources in 2002 and 2003. We improved a Wavelet-based Filter for determining Crop Phenology (WFCP) and developed a Wavelet-based Filter for evaluating the spatial distribution of Cropping Systems (WFCS) to the interpretation of MODIS time-series data to determine the spatial distribution of rice phenology and various rice-cropping systems from the seasonal Enhanced Vegetation Index (EVI) data. The findings correspond well the physical characteristics of the cropping system in the Mekong Delta, which have changed over time in response to localized and seasonal changes in water resources. One such example is the double-irrigated rice-cropping system commonly employed in the upper Mekong Delta in the dry season to avoid damage due to the subsequent floods. The shortage of suitable irrigation water and intrusion of saline water in the coastal regions during the dry season has constrained the practice dry-season cropping and has meant that the double- and single-rainfed rice-cropping systems are employed in the rainy season. A triple-irrigated rice-cropping system is used in the central part of the Mekong Delta which is located midway between the flood-prone and salinity intrusion areas. Analysis of annual changes in the rice cropping systems between 2002 and 2003 showed that the triple-cropped rice expanded to the flood- and salinity-intrusion areas. This expansion indicates that the implementation of measures to limit the extent of flooding and salinity intrusion by improved farming technologies and improvements in land management. The heading dates in the upper Mekong Delta in 2003 were earlier than in 2002 by approximately 20 to 30 days. The reasons for this would be due to decreased flood runoff in 2002 compared to 2001, and implementation of government policies regarding early sowing of dry-season crops. Subsequent analysis of the MODIS data confirmed that the spatial distribution of rice-cropping systems was closely related to seasonal changes in river runoff regime in the Mekong Delta.     

Promotion and prevention orientations in the choice to attend lectures or watch them online

When presented with the option to use a new instructional technology, students often face an approach–avoidance conflict. This study explored promotion and prevention orientations, concepts linked to approach and avoidance in Higgins's regulatory focus theory, in the choice to attend lectures or watch them online. Openness, a core disposition in the Big Five Model of personality, and positive attitudes towards the utility of the Internet, reflect promotion orientations that are potentially related to the choice to watch lectures online. By contrast, neuroticism, another core disposition in the Big Five Model, and anxiety about the Internet as a computer technology, reflect a prevention orientation that is potentially related to the choice of attending lectures in class. The results illustrate that both promotion and prevention are at work in the choice to attend lectures or to watch them online. Neuroticism and anxiety about the Internet as a computer technology were related to the choice to attend lectures in class, whereas the perceived utility of the Internet was related to the choice to watch lectures online. Instructional mode choice was not related to examination performance, suggesting that the choice to attend lectures or watch them online has more to do with individual differences in promotion and prevention orientations than with pedagogical characteristics that impact learning.     

Forward Observer system for radar data workflows: Big data management in the field

There are unique challenges in managing data collection and management from instruments in the field in general. These issues become extreme when “in the field” means “in a plane over the Antarctic”. In this paper we present the design and function of the Forward Observer a computer cluster and data analysis system that flies in a plane in the Arctic and Antarctic to collect, analyze in real time, and store Synthetic Aperture Radar (SAR) data. SAR is used to analyze the thickness and structure of polar ice sheets. We also discuss the processing of data once it is returned to the continental US and made available via data grids. The needs for in-flight data analysis and storage in the Antarctic and Arctic are highly unusual, and we have developed a novel system to meet those needs.We describe the constraints and requirements that led to the creation of this system and the general functionality which it applies to any instrument. We discuss the main means for handling replication and creating checksum information to ensure that data collected in polar regions are returned safely to mainland US for analysis. So far, not a single byte of data collected in the field has failed to make it home to the US for analysis (although many particular data storage devices have failed or been damaged due to the challenges of the extreme environments in which this system is used).While the Forward Observer system is developed for the extreme situation of data management in the field in the Antarctic, the technology and solutions we have developed are applicable and potentially usable in many situations where researchers wish to do real time data management in the field in areas that are constrained in terms of electrical supply.     

ICT Research in Africa: Need for a Strategic Developmental Focus

This paper argues the need to expand the research agenda on the use of ICT in African countries to include a stronger strategic developmental focus than is evident in much of the literature to date. Four strategic dimensions are identified, where ICT arguably has potential as a significant enabler for transformational development in Africa: institutional infrastructure; governance, accountability, and civil society; service production and economic activity; and access to global markets and resources. A representative set of literature on IS in Africa is classified along these dimensions, but an explicit focus on development is found to be lacking in most of this work. The four dimensions are then discussed in turn to describe their importance in the African context, to discuss some pathfinding research examples to date and to identify some directions for future research. The paper concludes with a call for IS researchers working on Africa to become involved in debate on national and international policy from an ICT perspective and to engage with other research communities in doing this, notably with those concerned with the field of African development.     

Writing power into online discussion

This article considers the way in which control of interaction emerges as a function of personal agency and external factors in a group of students engaged in online asynchronous text-based communication in a distance education program. It is structured around the argument that control is partly related to the power that individuals have to give effect to their wishes, but also acknowledges that this sense of agency is always in relation to the powers of others and more structural constraints. A picture emerges of the choices students make in deciding when to initiate discussion and respond to others, and about decisions concerning whose messages they would read and when. The impact of other students, of online groups, and instructors seems to play an important role in determining how participants participate in online interaction. Consideration of broader issues shows how the context in which students engage in interaction impacts the nature and extent of that interaction. The article concludes that being aware, and taking advantage of the socially grounded nature of online interaction provides the basis from which educators can act to ensure that interaction in online learning communities is enabling for the learning of all students.     

嵌入式多媒体应用的通用文件系统的分析和设计

随着嵌入式多媒体技术的日趋发展,越来越多的多媒体娱乐设施已经用于家用起居和娱乐场所。文中旨在提出和构建一个通用的、移植性强的、针对嵌入式系统上多媒体应用的文件系统来管理多媒体数据,提高数据的存取效率和存储设备的空间利用率,从而获得良好的视听效果。通过分析FAT文件系统的性能,以及比较在PC机和嵌入式系统上应用的优缺点,并结合多媒体数据本身的特殊性以及嵌入式的具体应用环境,对其进行改进,以实现优越的性能来适应嵌入式多媒体的应用。     

The adoption and diffusion of e-commerce in developing countries: The case of an NGO in Jordan

The case study in this research involves a nongovernmental organization (NGO) in Jordan in the Middle East, which attempted to utilize electronic commerce (EC) to streamline its business processes and information flow to businesses in Jordan and to other international businesses interested in the Jordanian market. The NGO managed to achieve these tasks expeditiously, and its EC initiative assisted in adding an effective digital parallel to existing systems and processes in this NGO. The NGO is directly involved in the e-government initiative empowered by H.M. King Abdullah II. At this end, with this royal support, the NGO successfully adopted EC. During the adoption and implementation process, the organization encountered numerous difficulties, as detailed in this research. However, the full success of EC was hampered by other factors. Initially, other governmental entities related indirectly to this NGO were not EC-ready. Second, although Web site utilization was growing in this NGO, most member merchants were reluctant to switch to the online arena and to abandon traditional practices in obtaining information and resources from this NGO. However, the NGO is aware of these concerns and envisages resolving such hurdles in its medium- to long-term projections. © 2007 Wiley Periodicals, Inc.     

Information technology in the National Curriculum: a view from Scotland

Abstract This paper examines the proposals for Information Technology (IT) in current curriculum developments in England and Wales and in Scotland. It points out significant differences between the pattern of curriculum developments in these two parts of the United Kingdom, noting in particular, that developments under the heading of The National Curriculum do not apply in Scotland. Nevertheless, IT developments in Scotland have many similarities to those in the rest of the UK and it is from this shared experience that a view is offered as to whether the proposals under The National Curriculum will allow IT to reach its full potential to shape the curriculum and to improve learning and teaching styles. Among the issues considered are the interplay between IT and the curriculum, the impact of IT on learning and teaching and the fundamental question as to whether the system—pupils, teachers, staff management and staff development arrangements—are likely to be able to respond to the National Curriculum proposals.     

The machine breakdown paradox: How random shifts in the production rate may increase company profits

The causes and effects of machine breakdowns have frequently been investigated in the past. One popular stream of research studies technical errors in production and analyzes their impact on the inventory policy of the company. In this paper, we show that random shifts in the production rate of a machine, which may occur, for example, due to technical defects, may lead to a reduction in total cost and therewith to an increase in profit. This obvious paradox may lead to situations where it is economically rational for the company to sustain a technically inefficient situation, or even to take measures to intentionally induce a shift in the production rate, for example by damaging the machine on purpose. In this paper, we illustrate this paradox by referring to an existing inventory model, and trace it back to common assumptions made in the literature.