语义缓存技术的研究

语义缓存技术一直以来是数据库研究的热点之一。语义缓存是指将用户向服务器端提交的查询语句和查询实际得到的结果数据同一存储在指定的缓存中,因而其不仅包含有数据,还有对数据的相关描述信息,从而可以提高查询效率。在语义缓存之前,还存在页面缓存,元组缓存,块缓存等缓存技术。本文首先介绍语义缓存的模型,然后阐述和分析语义缓存查询匹配算法和缓存替换策略,最后对语义缓存技术进行总结,从而为语义缓存技术的进一步研究提供一定的理论基础。     

关系数据库语义缓存的研究进展

语义缓存是优化数据库性能的有效方法,在关系数据库领域得到了广泛研究和应用。它是将查询结果和相关语义信息缓存,从而为将来的查询提供解答。本文首先介绍了语义 缓存的基本概念和原理,然后对现有语义缓存技术进行了分类,最后结合语义缓存的发展趋势讨论了语义缓存的关键技术。     

面向单表查询的具有语义缓存功能的ODBC接口设计

析了原有PsqlODBC不采用缓存技术带来的缺陷及其对系统性能的影响,提出在PsqlODBC中引入语义缓存技术,有效地利用了客户端的计算和存储资源,降低了服务器端的载荷,缩短了查询响应时间,提高了系统吞吐量。从语义缓存的内容、查询结果集与缓存结果集之间的关系、查询结果集的提取、数据更新和语义缓存的一致性等方面详细阐述了面向单表查询的具有语义缓存功能的ODBC接口设计。     

纯XML数据库语义缓存综述

介绍了语义缓存、XML查询语言等概念,对现有的多种纯XML数据库语义缓存技术及其实现、技术特点等进行了详细的阐述。在讨论了当前语义缓存的研究中遇到的新问题与挑战之后,介绍了一种语义缓存匹配视图的快速查找算法U ViewMatch,并总结了语义缓存的技术路线。     

自适应的数据库查询缓存

传统的缓存采取较为机械的管理方法,不能随数据库运行的动态信息调整自身参数以得到更优的性能。数据库语义缓存能够让数据库“理解”查询语义,可以为数据库的动态调节提供信息。而查询缓存是语义缓存的一种,在 SQL解析与查询执行之间,通过研究查询缓存的自主管理来提高数据库的查询性能。首先介绍了数据库常用的语义缓存与自主计算,然后对查询缓存进行了形式化定义,并提出了自适应的查询缓存模型。最后在MySQL的查询缓存上进行了实验,得到了较好的效果。     

基于语义缓存的移动查询导出

在移动环境下，客户缓存为提高客户－服务器数据库系统的整体性能，特别是保证客户端数据可用性提供了有效途径，该文针对如何从基于语义描述的缓存中导出当前查询（部分）结果的问题，研究了查询从缓存导出的充分条件，并在定义查询与缓存之间的精确匹配，包含匹配和相互匹配几种情况的基础上，给出缓存与查询，包含与相交匹配的判断条件和相应的算法，基于该文的研究，查询可以充分利用本地语义缓存的内容，从而降低网络开销，加快响应时间，并支持移动客户断接时的数据访问。     

面向海量数据统计分析查询的中间层语义缓存

海量数据库应用系统中对统计分析查询进行优化,缩短查询响应时间是系统性能提高的关键。中间层语义缓存提供了一种优化海量数据统计分析性能的途径。文章通过对中间层语义缓存的研究,提出了一个适合海量数据统计分析的中间层语义缓存解决方案。     

基于语义贡献值的XML查询缓存替换策略

传统缓存替换策略对语义缓存替换缺乏针对性,不能有效重用缓存中的数据,影响缓存命中率。为此,针对可扩展标记语言查询(XML)代数查询的特点,提出一种基于语义贡献值的XML查询缓存替换策略,根据用户历史查询的缓存项进行聚类分析,预测其对未来查询的语义贡献值,当缓存空间不足时替换语义贡献值最小的项,从而提高用户查询效率。实验结果表明,相比最不经常使用策略和最近最少使用策略,该策略能有效缩短查询时间,提高缓存命中率。     

子句间优化技术在语义缓存查询求值中的应用

缓存技术用来弥补网络通信能力的不足。语义缓存既缓存查询结果,也缓存查询语义,可更好节省网络开销。实用性是语义缓存技术产生和发展的基础,根据实用性要求,语义缓存查询求值所消耗的时空代价要远小于网络通信能力不足带来的时空代价,所以必须对求值算法进行优化。文章从语法一级分析求值算法存在的问题并给出了两级优化方法和实现技术,降低了算法复杂度,减少了对数据库的无效访问,使语义缓存技术向实用化迈进了一大步。     

面向聚集查询的语义缓存技术

将目前主要用于小规模数据库查询的语义缓存技术拓展到海量数据库的聚集查询中,以面向聚集查询的语义缓存形式模型为基础,构造了语义缓存StarCache.详细讨论了StarCache中的聚集查询处理、语义缓存替换管理和一致性维护等技术.StarCache已经集成在自主研发的并行数据库中间件StarTP中,并在一项大型国家工程中得到实际应用.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.