Internet环境下零件特征信息远程查询系统研究

以零件几何模型中的形状特征为信息共享单元，在Internet环境下开发了零件特征信息的元素级远程查询原型系统，并研究了该系统中的信息存储、查询和权限控制等关键技术．     

产品三维数据模型轻量化表示实现

提出一种能快速浏览的产品三维模型轻量化文件格式,文件中包含零件显示信息和几何信息·显示信息记录面的三角化模型和边的多边形模型,以加快模型的浏览速度,且按装配、零件、面、线、点层次关系进行组织;几何数据附加在显示信息上,提供几何数据的精确查询·文件大小通过数据压缩大幅度地减小,便于在网上发布·以此为基础开发了三维产品浏览系统和用于生成轻量化文件的接口程序·     

分级的行列级权限系统的设计和实现

为实现权限系统中用户授权的灵活性和数据级的权限控制,在传统权限访问控制模型的基础上,设计了一种基于内存数据库的分级的行列级权限控制模型。通过分级授权实现授权的灵活性和可继承性,通过分级行列级权限实现数据级权限控制,通过内存数据库和预排序遍历树算法实现数据的快速查询。开发了相应的软件系统,与传统权限模型进行了比较,结果表明了该模型的可行性和高效性。     

产品广义参数化设计的研究

分析了参数化设计的研究现状,提出了面向设计周期的产品广义参数化设计的概念,建立了从产品概念设计到详细设计的广义参数化信息模型,定义不同层次的参数映射和约束表达方法,通过主参数来封装产品几何信息和非几何信息,从而最终实现产品级、部件级与零件的参数化设计。     

箱体零件的功能特征模型定义方法研究

本文基于零件结构功能分解，研究了以功能特征为对象的箱体特征模型定义方法。用该方法建立箱体零件信息模型，实现了箱体结构功能与箱体几何特征之间的映射，并在满足箱体功能要求的前提下实现箱体的并行设计过程。     

基于XML的CAD/CAPP/CAM信息集成技术

在比较目前几种流行的系统集成技术的基础上 ,通过采用基于特征、面向对象的方法为产品几何数据和非几何数据建立信息模型 ,结合以计算机内部模型表达的产品定义数据 ,提出了一种基于 XML 标准的信息集成解决方案 ,并首次将 JDOM技术和 XQL查询技术珠联璧合地结合在一起实现对 XML文档高效地访问、操作 .该方案以灵活的数据模式、可重用的信息模块、易扩展的数据接口有效地、可靠地解决产品在设计和制造过程中信息的交换和共享 .     

一种新的B/S系统权限控制模型研究

将权限定义为由访问类型、信息对象、操作范畴和约束条件构成的四元组,并在此基础上建立包含权限编码生成器、权限编码分析器和权限编码库的基于权限四元组的权限控制模型4-TPBAC（4-Tuple Privilege Based Access Control）。介绍了模型中权限编码生成器和权限编码分析器的工作原理,分析了权限编码分析器中实现页面级权限控制、操作级权限控制和字段级权限控制等控制策略。     

国外基于特征设计的研究现状与展望

一、前言基于特征设计，简称特征设计。特征的概念是从工艺引出的，工艺规程是从毛坯到给定零件的转换过程，具体包括产品建模、选择机床、选择刀具组、选择加工时的装卡方案、确定切削序列和切削用量、设计夹具、确定刀具路径、编制数控机床加工程序等。为实现工艺规程的自动化，需要各种各样的信息，这些信息在设计好的零件三视图中已经存在，但可惜的是，当设计人员用几何实体造型方法在计算机上建立零件模型时，只保留了几何信息，而其他大量信息全丢失了！本文要讨论的特征设计恰恰能帮助我们克服这个问题。特征可以携带大量的工程信息…     

基于功能特征的零件建模技术

本文研究了一种人有人工智能性质的，以广义功能特征为对象的体特征模型定义方法，用该方法建立箱体零件信息模型，实现了箱体功能与箱体几何特征之间的映射，并在满足箱体功能的要求下实现箱体的几何设计与工艺设计交叉进行。     

国家科技奖励综合业务处理平台权限控制实现

应用用户／角色／任务权限／任务/权限的模型，实现了国家科技奖励综合业务处理平台的权限控制系统，阐述了权限控制系统的设计原则和方法。在开发过程中，将任务权限层加入T-RBAC模型，解决了任务细分困难的问题；在用户表中加入了结构信息，隔离了不同结构之间的数据信息；使用了字段子表，在Oracle内实现了字段级数据安全控制；使用权限信息表和数据库用户共同控制权限，对数据做了双层保护。用C#语言开发了C／S模式的权限控制系统图形界面，简化了权限控制，用户使用灵活方便。     

The dynamic predicate: integrating access control with query processing in XML databases

Recently, access control on XML data has become an important research topic. Previous research on access control mechanisms for XML data has focused on increasing the efficiency of access control itself, but has not addressed the issue of integrating access control with query processing. In this paper, we propose an efficient access control mechanism tightly integrated with query processing for XML databases. We present the novel concept of the dynamic predicate (DP), which represents a dynamically constructed condition during query execution. A DP is derived from instance-level authorizations and constrains accessibility of the elements. The DP allows us to effectively integrate authorization checking into the query plan so that unauthorized elements are excluded in the process of query execution. Experimental results show that the proposed access control mechanism improves query processing time significantly over the state-of-the-art access control mechanisms. We conclude that the DP is highly effective in efficiently checking instance-level authorizations in databases with hierarchical structures.     

基于NFA异构数据库集成系统的查询优化

XML文档信息容量的增长、数据敏感程度的增加,对异构数据源集成系统提出了新的挑战。为了降低查询复杂度、提高查询效率、增强数据库文档信息的安全性,本文采用感知情景因素的RBAC扩展模型,用一种新的基于XML的访问控制描述语言描述异构数据库集成系统中的访问控制策略,并使用查询优化技术,构造不确定性自动机(NFA)对用户查询进行重写。通过这些技术,最终过滤掉异构数据库集成系统中不符合安全策略的查询,实现细粒度的访问控制。     

Purpose based access control for privacy protection in relational database systems

In this article, we present a comprehensive approach for privacy preserving access control based on the notion of purpose. In our model, purpose information associated with a given data element specifies the intended use of the data element. A key feature of our model is that it allows multiple purposes to be associated with each data element and also supports explicit prohibitions, thus allowing privacy officers to specify that some data should not be used for certain purposes. An important issue addressed in this article is the granularity of data labeling, i.e., the units of data with which purposes can be associated. We address this issue in the context of relational databases and propose four different labeling schemes, each providing a different granularity. We also propose an approach to represent purpose information, which results in low storage overhead, and we exploit query modification techniques to support access control based on purpose information. Another contribution of our work is that we address the problem of how to determine the purpose for which certain data are accessed by a given user. Our proposed solution relies on role-based access control (RBAC) models as well as the notion of conditional role which is based on the notions of role attribute and system attribute.     

Examining topic shifts in content-oriented XML retrieval

Content-oriented XML retrieval systems support access to XML repositories by retrieving, in response to user queries, XML document components (XML elements) instead of whole documents. The retrieved XML elements should not only contain information relevant to the query, but also provide the right level of granularity. In INEX, the INitiative for the Evaluation of XML retrieval, a relevant element is defined to be at the right level of granularity if it is exhaustive and specific to the query. Specificity was specifically introduced to capture how focused an element is on the query (i.e., discusses no other irrelevant topics). To score XML elements according to how exhaustive and specific they are given a query, the content and logical structure of XML documents have been widely used. One source of evidence that has led to promising results with respect to retrieval effectiveness is element length. This work aims at examining a new source of evidence deriving from the semantic decomposition of XML documents. We consider that XML documents can be semantically decomposed through the application of a topic segmentation algorithm. Using the semantic decomposition and the logical structure of XML documents, we propose a new source of evidence, the number of topic shifts in an element, to reflect its relevance and more particularly its specificity. This paper has three research objectives. Firstly, we investigate the characteristics of XML elements reflected by their number of topic shifts. Secondly, we compare topic shifts to element length, by incorporating each of them as a feature in a retrieval setting and examining their effects in estimating the relevance of XML elements given a query. Finally, we use the number of topic shifts as evidence for capturing specificity to provide a focused access to XML repositories.     

An effective approach for the protection of privacy text data in the CloudDB

Due to the advantages of pay-on-demand, expand-on-demand and high availability, cloud databases (CloudDB) have been widely used in information systems. However, since a CloudDB is distributed on an untrusted cloud side, it is an important problem how to effectively protect massive private information in the CloudDB. Although traditional security strategies (such as identity authentication and access control) can prevent illegal users from accessing unauthorized data, they cannot prevent internal users at the cloud side from accessing and exposing personal privacy information. In this paper, we propose a client-based approach to protect personal privacy in a CloudDB. In the approach, privacy data before being stored into the cloud side, would be encrypted using a traditional encryption algorithm, so as to ensure the security of privacy data. To execute various kinds of query operations over the encrypted data efficiently, the encrypted data would be also augmented with additional feature index, so that as much of each query operation as possible can be processed on the cloud side without the need to decrypt the data. To this end, we explore how the feature index of privacy data is constructed, and how a query operation over privacy data is transformed into a new query operation over the index data so that it can be executed on the cloud side correctly. The effectiveness of the approach is demonstrated by theoretical analysis and experimental evaluation. The results show that the approach has good performance in terms of security, usability and efficiency, thus effective to protect personal privacy in the CloudDB.     

安全数据库隐私保护和访问控制集成研究*

数据库数据的合法使用和隐私保护是现代安全数据库系统面临的新挑战。针对目前单方面考虑隐私保护或访问控制技术难以同时满足数据库信息安全和处理性能需求的不足,提出一种集成访问控制和隐私保护技术的安全数据库模型,通过建立查询审计隐私保护模型中的查询可疑性与授权视图访问控制模型中查询有效性之间的关系,形成统一的查询判断方法,并给出多项式时间复杂度的审计算法和集成的安全检查框架,以同时实现数据库系统隐私保护和访问控制的安全功能。     

Mobile broadcast services with MIMO antennae in 4G wireless networks

The deployment of wireless data broadcast to empower mobile information services as a resource-conserving means offers significant benefits due to the scalability feature offered by the technology. In this paper, we present a novel and holistic data broadcast management approach in 4 G wireless networks with multiple-input multiple-output (MIMO) antennae. The proposed scheme consists of three elements, namely: (i) broadcast ordering; (ii) Global indexing; and (iii) merging data structure. With the integration of these elements, we expect to obtain substantial efficiency for mobile computing clients when retrieving data on-air. We have experimentally evaluated the performance of the proposed model including comparison with the relevant schemes. The results from the experiments affirm the effectiveness of our proposed approach in respect to minimizing query access time and conserving energy utilization of the clients.     

Dealing with feature interactions for prismatic parts in STEP-NC

Determining the precedence of machining features is a critical issue in feature-based process planning. It becomes more complex when geometric interaction occurs between machining features. STEP-NC, the extension of STEP (ISO 10303) standard developed for CNC controllers, is a feature-based data model. It represents all the geometric and topological product data minus feature interactions. In this paper, machining precedence of interactive and non-interactive STEP-NC features is discussed. Local and global precedence of machining features are defined on the basis of geometric constraints, such as geometric interaction of features and feature approach face and technological constraint such as access direction of the cutting tool. A software tool has been developed to visualize the STEP-NC part model and to generate the graphs of feature interaction and feature precedence. The output can be then used to augment the STEP-NC data in order to generate the optimal sequence of operations.     

Query optimisation using a data dictionary

Data dictionaries are playing an increasingly important role as repositories for information about all the data belonging to an organisation. Through the provision of sophisticated end user facilities, database management system implementors are encouraging high-level interface access to databases. However, it is often alleged that this type of database access is very costly. In this paper we describe the use of a data dictionary in the implementation of a high-level query interface to CODASYL databases. A feature of the query interface is its use of database monitoring information, stored in the data dictionary, to optimise the processing of queries.