一种基于变窗口的数据流连续查询方法

目前对数据流连续查询的研究工作大部分基于滑动窗口,窗口大小固定不变.本文从内存资源有限性与查询结果精确性角度出发,采用可变窗口技术,在缓存中加入窗口控制器,当数据到达缓存时,根据用户提出查询具体问题和数据流速情况,窗口分配算子对其进行窗口大小的划分.使得在内存资源有限的情况下,通过动态改变滑动窗口大小,充分利用系统资源,降低内存使用率的同时,使连续查询的查询结果都在允许的误差范围内,此方法经过验证是可行的.     

CAD/CAM网站中动态页面的设计

介绍了CAD CAM网站中动态页面的设计。为了实现用户与网站的交互功能 ,在词汇查询与问题讨论部分采用ASP技术 ,使本站能够根据用户的需求在数据库中调取相关数据 ,动态生成页面。     

浅论Solidworks中尺寸公差标注的二次开发

主要介绍了以VB为开发工具,用ACCESS建库,利用Solidworks OLE应用程序开发接 口API函数实现Solidworks中尺寸公差查询模块系统的研究和开发。该模块解决了Solidworks中不 能动态查询尺寸公差的问题。     

ORACLE10g数据库技术查询性能浅谈

随着计算机应用的深入,应用数据也随着日常工作而迅速增长,作为数据仓库的数据库的重要性也日益显著.在数据库的各种操作中,数据库查询所占的比重最大,也是用户经常使用的功能之一.笔者首先介绍了数据库查询原理,然后介绍了数据库的通用查询语言工具,同时通过具有代表性的实验讲解了数据库查询性能的优化.并就数据库查询性能进行介绍和探索.     

基于IC卡及TTS模块的学生信息语音查询系统设计

介绍一种基于IC卡和科大讯飞TTS语音模块的学生综合信息语音查询系统.利用单片机系统接收IC卡读卡器读出学生卡的ID信息,经确认学生有效身份信息后,通过LCD及语音模块显示或播报学生综合信息,如成绩、选课、教师及其他个人校园通知信息.文中给出了系统的详细硬件设计方案及主要软件流程图.该系统除可为学生提供综合的信息查询服务外,还可用于收集学生对学校各项工作的反馈意见,并在通过上位机软件提取相关信息后,为学校改善各项教学及管理工作提供依据.     

数据库的模糊查询技术

给出了一种利用模糊数学的贴近度进行信息查询的模糊处理方法,拓宽了信息查询的应用范围,使得在不完整语义或歧义描述下可获得较为完整的信息。     

Providing Security and Interoperation of Heterogeneous Systems

Interoperation and information sharing among databases independently developed and maintained by different organizations is today a pressing need, if not a practice. Governmental, military, financial, medical, and private institutions are more and more required to become part of a distributed infrastructure and selectively share their data with other organizations. This sharing process inevitably opens the local system to new vulnerabilities and enlarges the space of possible threats to the data and resources it maintains. As a complicating factor, in general, data sources are heterogeneous both in the data models they adopt and in the security models by which protection requirements are stated. We present a modeling and architectural solution to the problem of providing interoperation while preserving autonomy and security of the local sources based on the use of wrappers and a mediator. A wrapper associated with each source provides a uniform data interface and a mapping between the source's security lattice and other lattices. The mediator processes global access requests by interfacing applications and data sources. The combination of wrappers and mediator thus provides a uniform data model interface and allows the mapping between restrictions stated by the different security policies. We describe the practical application of these ideas to the problem of trusted interoperation of health care databases, targeted to enforcing security in distributed applications referring to independent heterogeneous sources protected by mandatory policy restrictions. We describe the architecture and operation of the system developed, and describe the tasks of the different components.     

The complexity and approximation of fixing numerical attributes in databases under integrity constraints

Consistent query answering is the problem of characterizing and computing the semantically correct answers to queries from a database that may not satisfy certain integrity constraints. Consistent answers are characterized as those answers that are invariant under all minimally repaired versions of the original database. We study the problem of repairing databases with respect to denial constraints by fixing integer numerical values taken by attributes. We introduce a quantitative definition of database repair, and investigate the complexity of several decision and optimization problems. Among them, Database Repair Problem (DRP): deciding the existence of repairs within a given distance to the original instance, and CQA: deciding consistency of answers to simple and aggregate conjunctive queries under different semantics. We provide sharp complexity bounds, identifying relevant tractable and intractable cases. We also develop approximation algorithms for the latter. Among other results, we establish: (a) The -hardness of CQA. (b) That DRP is MAXSNP-hard, but has a good approximation. (c) The intractability of CQA for aggregate queries for one database atom denials (plus built-ins), and also that it has a good approximation.     

An ASN.1 Model and Integration Approach for Structured Text

A language for manipulating ASN.1 print files is defined as an addition to the ASN.1 data definition language as specified in the ISO standards 8824 and 8825. The language has syntax similar in spirit to SQL, and provides analogous operations. Together, ASN.1 and the manipulation language define a model that can represent attribute hierarchies, multivalued attributes, optional attributes, both ordered and unordered attributes and tuples, and unnamed attributes—constructs that are absent in the traditional relational model. In addition, the proposed model allows the semantics of order, homogeneity, optionality, choosability, and uniqueness to be attached to constructs and construct elements. The approach is well suited for modeling data where form is important, such as text and flat file databases having ad hoc formats. It also supports modeling relations. The primary motivation for developing this language is to provide a common model for a database integration approach where some of the databases are in the form of formatted flat file text, while others are relational. Although the approach is general and can be applied in many different areas, scientific database and tool integration was the primary motive for its development.     

Supporting personalized ranking over categorical attributes

This paper studies how to enable an effective ranked retrieval over data with categorical attributes, in particular, by supporting personalized ranked retrieval of highly relevant data. While ranked retrieval has been actively studied lately, existing efforts have focused only on supporting ranking over numerical or text data. However, many real-life data contain a large amount of categorical attributes, in combination with numerical and text attributes, which cannot be efficiently supported - unlike numerical attributes where a natural ordering is inherent, the existence of categorical attributes with no such ordering complicates both the formulation and processing of ranking. This paper studies the efficient and effective support of ranking over categorical data, as well as uniform support with other types of attributes.