Document replication strategies for geographically distributed web search engines

Large-scale web search engines are composed of multiple data centers that are geographically distant to each other. Typically, a user query is processed in a data center that is geographically close to the origin of the query, over a replica of the entire web index. Compared to a centralized, single-center search engine, this architecture offers lower query response times as the network latencies between the users and data centers are reduced. However, it does not scale well with increasing index sizes and query traffic volumes because queries are evaluated on the entire web index, which has to be replicated and maintained in all data centers. As a remedy to this scalability problem, we propose a document replication framework in which documents are selectively replicated on data centers based on regional user interests. Within this framework, we propose three different document replication strategies, each optimizing a different objective: reducing the potential search quality loss, the average query response time, or the total query workload of the search system. For all three strategies, we consider two alternative types of capacity constraints on index sizes of data centers. Moreover, we investigate the performance impact of query forwarding and result caching. We evaluate our strategies via detailed simulations, using a large query log and a document collection obtained from the Yahoo! web search engine.     

基于分布式数据库的房地产管理信息系统的设计与实现

本文对房地产管理信息系统设计方案中的分布式数据库技术进行了详细阐述,包括分布式数据库的设计原则、系统结构、分布式查询与数据更新等内容.     

A theory of instruction for introductory programming skills

ABSTRACT

Background and Context: Current introductory instruction fails to identify, structure, and sequence the many skills involved in programming.

Objective: We proposed a theory which identifies four distinct skills that novices learn incrementally. These skills are tracing, writing syntax, comprehending templates (reusable abstractions of programming knowledge), and writing code with templates. We theorized that explicit instruction of these skills decreases cognitive demand.

Method: We conducted an exploratory mixed-methods study and compared students’ exercise completion rates, error rates, ability to explain code, and engagement when learning to program. We compared material that reflects this theory to more traditional material that does not distinguish between skills.

Findings: Teaching skills incrementally resulted in improved completion rate on practice exercises, and decreased error rate and improved understanding of the post-test.

Implications: By structuring programming skills such that they can be taught explicitly and incrementally, we can inform instructional design and improve future research on understanding how novice programmers develop understanding.     

Computing and STEM in Greek tertiary education: gender representation of faculty members during the decade 2003–2013

This study focuses on the investigation of gender representation of faculty members of all ranks (professors, associate professors, assistant professors and lecturers) of Computing and STEM (Science, Technology, Engineering and Mathematics) in Greek tertiary education during the decade 2003–2013. To this end, a quantitative study was conducted, taking into account appropriate data derived from the Hellenic Statistical Authority. The data analysis shows that during the said decade, (a) faculty members in Computing and in each discipline of STEM constituted a small part of the total number of Greek faculty members; (b) for every single year of the decade, females were less prevalent than males in all ranks of faculty members in Computing and Engineering; (c) the situation for females in the Computing faculty appears to have been even worse, as the percentage of them in every rank was the lowest among the STEM disciplines studied for all or most of the years of the decade under study; and (d) although females were better represented in the position of lecturer, which constituted the fewest faculty members in the aforementioned disciplines, highly populated ranks of faculty members were dominated by males.     

Impact of distributed leadership on teacher job satisfaction in China: The mediating roles of teacher autonomy and teacher collaboration

Teacher job satisfaction is a heated topic worldwide. Among the possible factors influencing teacher job satisfaction, distributed leadership is very important one. Given very few studies have investigated the effects of distributed leadership on teacher job satisfaction through teacher autonomy and teacher collaboration, this paper is important. It is expected to provide international readers with a better understanding of how these variables are practised in the Chinese context. Specifically, we aim to achieve two goals. The first goal is to investigate the direct impact of distributed leadership on teacher job satisfaction and the second one is to explore how distributed leadership indirectly affects teacher job satisfaction through teacher autonomy and teacher collaboration. The data are from the 2018 Teaching and Learning International Survey (TALIS) (n = 3976). Structural equation modeling revealed statistically significant positive effects of distributed leadership on teacher autonomy, teacher collaboration, and teacher job satisfaction, respectively. The further analyses indicated that the indirect effects of distributed leadership on teacher job satisfaction through teacher autonomy and professional collaboration were statistically significant. However, distributed leadership had no indirect effect on job satisfaction via exchange and co-ordination. Based on the findings, we propose some suggestions to improve teacher job satisfaction, such as strengthening communications between school leaders and teachers, and providing adequate autonomy to teachers. The detailed relationships among these variables are discussed in connection with Chinese educational context.     

基于云计算技术的数字生态城市平台设计

针对国内外数字城市建设计中存在的一些不足,本文提出了数字生态城市云平台的解决方案。该平台是数字生态城市DigitalCity和云计算服务平台的融合,解决同时操作多源、海量和异构的城市基础数据,实现分布式信息资源的共享与交换,提供分布式的按需服务等功能。DCPaaS数字生态平台针对数字生态城市的大环境,实现了业务自动部署和托管运行、专业化集中式维护等功能,为创建良好的数字生态城市服务创新环境提供了必需的技术支撑。     

配电网继电保护的现状与展望

文章论述了当前配电网中常见的继电保护类型,讨论了它们的优点和不足,并在此基础上分析和指出了配电网继电保护的发展方向.     

发展特色鲜明的一般本科院校信息与计算科学专业——以成都信息工程学院为例

成都信息工程学院信息与计算科学专业结合培养目标和社会实际需求,在专业定位上,突出＂数学基础扎实,理工融合＂的特色;在课程设置上,合理设置专业必修课程,优化选修课程,调整理论教学与实验教学的比例,对课程进行模块化设计;在专业实践教学上,建立＂课内实验—课内实验与课外实践—课外实践—综合实践＂的多层次、逐步递进的阶梯型实践教学体系。实践表明,找准专业定位,明确专业办学特色对办好本专业起到至关重要的作用。     

情感计算在网络远程教育系统中的应用：功能、研究现状及关键问题

情感能力是人类智能的重要标志,情感的缺失会影响网络远程教育的教学质量和学习者的学习效果。情感计算是和谐人机交互与人工智能领域中新的研究方向。在网络远程教育系统中应用情感计算理论与技术,可以进一步优化网络远程教育的功能,帮助教师监测远程学习者的情感变化,调整教学策略和方法,实时给予学习者情感反馈,使教学质量达到最佳。目前国内外情感计算在远程教育方面的应用研究还处于起步与探索阶段,所构建的远程教学系统对远程教学中师生情感生理特征与心理特征、多模情感信息融合机制及网络虚拟人机情感交互特性等考虑不足,系统原型在情感合成与表达、智能人机情感交互实现上存在着很大的难度。因此,构建与人类情感系统相吻合的、自然和谐的、人性化和智能化的网络远程教育系统,需要有效解决师生面部表情、语音情感特征信号的准确识别与提取,师生多模情感信息融合机制与和谐人机情感交互技术等关键问题。     

基于移动云计算的个人学习环境支持系统的构建研究

本文基于移动云计算和Mashup技术构建个人学习环境支持系统,为学习者提供符合个性化的知识与学习资源的信息推送与引导,即时获取和存储在云端的学习资源,实现任何时间、任何地点实时满足学习者的学习需求,为进一步研究基于移动互联网环境下的提升高校教学能力的深入挖掘提供依据。