基于实体语义的多级安全数据模型

提出了一种基于实体语义的多级安全数据模型。该模型借鉴了Smith-Winslett模型基于置信的语义和MLR模型数据借用的思想。定义了ESM数据模型,并捕述了它的4个完整性性质和4个数据操作。ESM模型消除了语义模糊性,同时又保持了向上的信息流。证明了ESM模型的正确性、完备性和安全性。     

多实例的多级安全关系数据库数据模型研究

现有的基于多实例的多级安全数据模型中，存在着语义的二义性问题和更新操作的元组增生问题，增加了系统实现和用户操作的复杂度，也存在着潜在的安全隐患，本文系统地结合多实例和伪元组的概念，以形式简单，易于实现并避免引入隐通道为原则，对上述模型进行了改进，提出了一个新的“同级读，同级写”的多级安全数据模型。     

一种多级安全数据模型中的多实例语义

为了对低安全级的主体(用户)隐藏高安全级的敏感信息,在多级安全数据模型中引入了多实例的概念.关于多实例的语义以及维护一直是多级安全数据模型的研究热点.提出了一种新的多实例语义MLS-POS,并给出了该语义下维护多实例的方法. MLS-POS最大的特点是能够限制低级别用户修改高级别数据的程度,弱化高级别数据与低级别数据的依赖关系,在该语义下维护多实例元组时更具安全性与合理性.     

一个适合复杂对象管理的层次—关系模型

本文提出了管理复杂对象实用而经济的数据模型－“层次－关系“模型。ＯＯＤＢ方法无疑是处理复杂对象有效的方法，然而实现一个纯粹的ＯＯＤＢＭＳ其工作量和复杂度都难以在近期使用它。语义联系模型在表达客观事物的语义联系上有其独特的功能，而描述复杂对象的内部结构则显得力不从心。基于传统数据模型组合和扩充的“层次－关系“模型，吸取ＯＯＤＢ静态结构继承的思想，利用了层闪模型和关系模型已有的技术和其优点，是处理复杂     

多级安全数据模型的主键漏洞问题及消除方法

随着多级安全数据库研究和实际应用的深入,对多级安全数据模型提出了新的要求。文章对现有多级安全数据模型具有的主键漏洞问题进行了详细分析和描述,并针对MLR模型提出了相应的改进方法。     

一种安全数据库多级安全模型与外键引用研究

提出一个新的安全数据库关系模型,包括一个多级安全模型和增强的外键引用功能.在多级安全模型中,通过扩展了Sandhu的MLR模型给出新的语义,使之描述现实世界更加合理和实用.另外,增强的外键引用功能提高了系统建模的能力.     

多级环境下基于角色和本体的访问控制方法

为了解决多级环境中敏感资源的安全性问题,提出了多级环境下基于角色和本体的访问控制方法.通过使用本体等语义技术,构造了一个结合基于角色的访问控制和Bell-LaPadula (BLP)模型的访问控制模型.根据角色的继承关系推导用户及资源之间安全级别的高低关系,在为角色指派权限时按照BLP模型进行授权的限制.实验表明,该方法在保证多级安全特性的前提下实现了用户权限的自动分配,消除了角色权限继承带来的安全隐患,为多级环境下的访问控制提供了一种新的思路.     

一种紧凑的多级安全关系数据模型

针对现有多级关系数据模型中存在的数据重复率大、复杂安全格的置信不明确、主键漏洞等问题,该文定义了一种新的多级安全关系数据模型—CMLR。该数据模型继承多个现有数据模型的优点,重定义了完整性规则和操作语义,通过采用基表和衍生表、实体标识符、显式和隐式置信等手段,将数据重复率由元组级降至元素级,明确了复杂安全格的置信规则,消除了主键漏洞。CMLR模型能够有效地提供元素级的强制访问控制。     

面向对象数据库的安全模型及其应用

近年来,数据库安全模型一直是数据库方面研究的热点。由于关系数据模型是建立在良好的数学模型的基础上,因而成熟的关系数据安全模型已经被提出。而面向对象数据模型本身尚未找到坚实的数学基础,针对面向对象数据库的安全模型研究不多,文章在这方面做了一些尝试,它提出了一种基于视图的面向对象数据库的信息过滤模型。该模型以多级数据模型为基础,综合了视图模型和信息过滤模型的优点;然后给出该模型的评价及其应用。     

基于扩展客体层次结构的安全数据库策略模型

安全策略模型是安全可信系统的基础.Bell-LaPadula模型是多级安全系统中广泛应用的安全策略模型,但它缺乏针对数据模型的完整性和一致性规则.以该模型为基础,针对数据库系统的数据模型,提出了一个以扩展客体层次结构为基础的安全策略模型.模型通过扩展客体层次结构使完整性成为模型的内在属性,并引入或重新定义了客体域、扩展安全公理和操作规则.模型更加适应多级安全数据库系统的要求,增强了策略模型与系统规格和高层模型的一致性.普遍性和通用性安全模型的扩展和增强,特别是安全性以外的特性的引入是安全策略模型向实际系统模型转化的必要步骤.     

密码学多层次教学实践

本文根据多年的教学实践,探讨了教学内容的选择和组织、实验教学组织和自主实验设计等。     

脱机手写体汉字识别后处理综合纠错算法设计和实现

充分利用了汉语词的信息及字词的频度信息，利用面向对象技术并用多级的纠错方法，实现了一个基于综合算法的汉字识别后处理系统，明显地提高了脱机手写体汉字最终识别率。     

Toward a deeper understanding of IT adoption: A multilevel analysis

This study adopts a multilevel perspective and uses cross-level modeling to explore how resistance to change (RTC) influences information technology (IT) adoption behaviors. RTC is conceptualized at two levels of analysis (personal and contextual) and with two levels of specificity (distal and proximal). Data were collected from 258 employees within 25 administrative work units undergoing a new IT initiative. The findings from this study reveal a “maverick effect” wherein pro-initiative employees react in contrast to their workplace contexts. They champion IT adoption when their work units resist the IT initiative and prolong IT adoption when their work units readily embrace the IT initiative. This study introduces a novel interactionist perspective on IT adoption that considers employee dispositions and perceptions, as well as workplace climate and culture, as enablers and inhibitors of IT adoption. Moreover, the study advocates for change management practices that account for multilevel interactions among the personal and contextual influences of IT adoption.     

多电平变换器拓扑结构的发展与现状

本文介绍了多电平变换器拓扑结构的发展和现状,以及实现多电平变换器的基本电路,包括二极管箝位型、飞跨电容型、级联型、通用型、直流源级联型、变压器级联型等,列出了它们的基本电路拓扑图,同时对拓扑图进行了简单的分析,总结了各种拓扑结构的特点。最后,对多电平变换器的发展方向提出了看法。     

The influence of individual and contextual work factors on workers' compliance with health and safety routines

This study investigated the relationships between workers’ compliance with health and safety (H&S) routines and instructions adopted in the company (dependent variable) and psychological demands, decision authority, social support, management support, unionization and H&S management system (independent variables). A cross-sectional questionnaire study was performed among 1051 workers and the managers of 102 small- and medium-sized motor vehicle repair garages. Multilevel modeling was performed to account for the hierarchical structure of the data. At the worker level, high compliance with H&S routines correlated significantly with both social support and H&S-related management support. At the garage level, mean management support and a well-developed H&S management system correlated significantly with high workers’ compliance. Changing both the individual and contextual factors in the work environment may thus increase workers’ participation in H&S activities.     

A multilevel approach for learning from labeled and unlabeled data on graphs

The recent years have witnessed a surge of interest in graph-based semi-supervised learning methods. The common denominator of these methods is that the data are represented by the nodes of a graph, the edges of which encode the pairwise similarities of the data. Despite the theoretical and empirical success, these methods have one major bottleneck which is the high computational complexity (since they usually need to solve a large-scale linear system of equations). In this paper, we propose a multilevel scheme for speeding up the traditional graph based semi-supervised learning methods. Unlike other accelerating approaches based on pure mathematical derivations (like conjugate gradient descent and Lanczos iteration) or intuitions, our method (1) has explicit physical meanings with some graph intuitions; (2) has guaranteed performance since it is closely related to the algebraic multigrid methods. Finally experimental results are presented to show the effectiveness of our method.     

板问题预条件子在曙光D1000+上的MPI实现

１．引言 在求解由偏微分方程引出的大规模线性系统时,多水平方法已经成为强有力的工具．多水平预条件子的构造在理论上已有大量的文献［１,４,８－１２］．在对多水平预条件子构造时,一般需要嵌套的网格和空间,这对高阶有限元和非协调元来说是十分困难的．许学军在其博士论文中［７］通过引入辅助的嵌套的低阶有限元空间（四阶问题为ＢＦＳ和ＰＳ元）和插值算子来解决这个问题,构造了最优的预条件子（相似的构造见［１０］）． 一般地,对于大规模的线性系统,我们不用直接法求解,而是用共轭梯度法等迭代方法求解［３］．当用 ＣＧ…     

OPC技术在碳素阳极生产过程多级控制系统中的应用

介绍了OPC技术及其应用前景,提出了一种可用于某厂碳素阳极过程控制的、基于OPC技术的多级计算机控制系统.该系统可实现现场操作级、工程师站、专家站的信息共享,可组成一种开放的(Open)、公共的(Nonproprietary)、即插即用的(Plug-And-Play)工业实时监控系统(ONPS)[1].     

Design of educational and ICT conditions to integrate differences in learning: Contextual learning theory and a first transformation step in early education

Educational differentiation and ICT can be designed to better recognize and integrate learning differences across students particularly by assisting instructional management and the self-regulation of students. A conceptual framework for such practice is elaborated here. First, learning as an interactional co-constructive process at various levels is considered. The diagnostic, instructional, management, and system aspects of the learning process can be stimulated and maximized. Second, differentiation of learning procedures and materials, design of integrating ICT support, and improvement of development and learning progress are recommended as contextual conditions to optimize the learning process. The combination of the learning aspects with these contextual conditions provides theoretical guidelines for the transition from a nondifferentiating system of education to a differentiating, ICT-based system of instructional management for all students. Information is given about the realization of two of the differentiation guidelines and all ICT design guidelines. The first products were used in kindergarten, to start the improvement of educational practice. This occurred in co-development with kindergarten teachers of three Dutch kindergartens. Information is given about the process and outcomes of this first transformation step in practice. Finally, next co-development steps are discussed.     

Institutionalised ICT use in primary education: A multilevel analysis

This study uses a multilayered framework of different independent school and teacher variables to study which factors are related to the use of ICT for teaching and learning in Flemish (Belgium) primary schools. Special attention is paid to widely accepted technology uses by teachers, which is labelled as ‘Institutionalised ICT use’. A questionnaire has been administered to a representative teacher sample (N = 433) in 53 Flemish primary schools. Factor analyses and multilevel hierarchical regression analyses have been conducted. The results of the multilevel analysis show that ‘Institutionalised ICT use’ should not only be considered as a teacher phenomenon but also as a school phenomenon. The null model shows that about 14% of the variance in ICT use of teachers is due to between-school differences. In a final model, the variables ‘ICT professional development’, ‘ICT competences’, ‘developmental educational beliefs’, and ‘schools' ICT vision and policy’ showed a positive association with ‘Institutionalised ICT use’.