深入浅出看视图

提示:本文对视图的概念进行了讲解,通过例子对视图的操作进行了分析。给出了视图在数据库应用系统开发中的作用的系统描述。在关系数据库中,视图是从一个或几个基本表(或其它视图)导出的表。与基本表不同,视图是虚表。数据库中只存放视图的定义,而不存放视图对应的数据,这些数据仍存放在原来的基本表中;基本表中的数据发生变化,从视图中查询得出的数据也就随之改变。视图是关系数据库系统提供给用户以多种角度观察数据库中数据的重要机制。视图—经定义,就可以和基本表一样被查询和删除,也可以在一个视图之上再定义新的视图,但对视图的修改(…     

一个基于视图的数据访问模型

多用户共享一个数据库必然存在一些安全隐患,须加以特定的控制措施以防止非法访问。提出一个基于视图的数据访问模型(VBAC),根据用户名创建与之联系的视图(视图成为该用户访问属于他的数据的惟一窗口),回收所有用户的权限,并将视图的访问权限授予给与之对应的用户,当一个用户登录系统,将他与对应的视图绑定起来,用户的数据访问通过视图间接完成,一旦回收视图的授权,与之对应的用户将不能对数据库进行任何存取。通过授权的数据视图,将用户对数据的操纵限定在特定的行和列,在用户和数据库之间建立信息安全防火墙。在Microsoft SQL Server 2000下测试了该模型的有效性。     

一个基于视图的数据访问模型

多用户共享一个数据库必然存在一些安全隐患,须加以特定的控制措施以防止非法访问.提出一个基于视图的数据访问模型(VBAC),根据用户名创建与之联系的视图(视图成为该用户访问属于他的数据的惟一窗口),回收所有用户的权限,并将视图的访问权限授予给与之对应的用户,当一个用户登录系统,将他与对应的视图绑定起来,用户的数据访问通过视图间接完成,一旦回收视图的授权,与之对应的用户将不能对数据库进行任何存取.通过授权的数据视图,将用户对数据的操纵限定在特定的行和列,在用户和数据库之间建立信息安全防火墙.在Microsoft SQL Server 2000下测试了该模型的有效性.     

关于面向对象数据库系统中用户视图机制的研究

面向对象数据库的模式是按照对象信息的内涵制定的,考虑的因素包括对象的分类、概括、综合、聚集及其所描述的不同类型对象间的联系等。然而不同用户对这些复杂信息的覆盖面有不同的要求,且不一定与系统的数据库模式恰好吻合,这就向面向对象数据库系统(OODBS)提出了支持用户视图、进行数据重构的要求。本文就引入用户视图机理到OODB 中的方法进行了探讨,给出了面向对象用户视图的定义与描述,并讨论了与之相关的数据字典信息,最后提出了建立用户视图所应遵循的原则。     

OLAP系统中用户的会话视图

1.前言在数据库系统中,视图是由基表或其它视图导出的虚表,只在数据目录中保留其逻辑定义,而不作为一个表实际存储在数据库中。数据库管理员可以为特定的用户或用户群定义一个或多个视图,以限制或引导他们对数据库的访问。用户也可以定义视图,把自己的视野集中在有意义的范围内。在文[1]中,提出了Web用户视图的概念,将Web用户的注意力限制在其感兴趣的范围内。     

网格环境下的数据库访问和集成

为了集成网格环境中的数据库资源,促进网格应用支持现有数据库的访问,提出一种基于服务的数据库访问和集成系统(GridDBAdmin)。GridDBAdmin为用户提供了虚拟的全局逻辑数据库视图,支持用户使用现有的SQL语言同时访问多个数据库。系统由元数据服务和网格虚拟数据库服务构成。其中元数据服务负责发现含有用户所需数据的数据库,网格虚拟数据库服务提供全局逻辑视图,通过分布式查询机制将用户的SQL请求分解到具体的数据库中并进行结果合并。对基于Globus和OGSA-DAI工具包开发的原型系统进行了测试,得到了较好的结果。     

Visual Foxpro 视图性能优化方法

Cisual FoxPro(以下简称VFP)以其功能强大,面向对象,支持客户机／服务器等诸多优点,已广泛应用于数据库开发领域。在数据库应用中,信息的快速检索和更新起着极为重要的作用。若想为应用建立一个查询和修改相结合的数据集,可以使用视图。视图能够从一个或多个相关表中提取一套数据;也可以使用视图更新所提取的信息并将更新后的结果送回源表或基表中。视图是VFP数据库的一个新特点,有效地使用视图,可以充分发挥VFP的数据访问的高性能特点。但是,并非所有的使用者都能有效地使用VFP的视图技术。相反,往往由于对视图使用不当,     

视图技术在大型数据库系统中的应用

１引言 ＭＳ ＳＱＬ Ｓｅｒｖｅｒ是 Ｍａｃｒｏｓｏｆｔ公司开发的大型数据库系统。在大型数据库系统应用中,信息的快速检索和更新起着极为重要的作用,若想为应用系统建立一个查询和修改相结合的数据集,可以使用视图。视图能够从一个或多个相关表中提取数据（查询）,也可以使用视图更新所提取的数据,并将更新后的结果送回到基表中（修改）。在 ＭＳ ＳＱＬ Ｓｅｒｖｅｒ中通过使用视图技术对数据库（表）的数据进行插入、修改、查询、删除等操作,可以使这一大型数据库系统的复杂应用简单化。２视图概念 在数据库管理系统中,用户数据…     

基于规则面向用户的动态视图的实现

PostgreSQL是一种对象关系型数据库管理系统.利用PostgreSQL的规则系统,实现了一种面向用户的动态视图建立的方法.该方法利用PostgreSQL的系统表、系统函数,通过创建视图的插入、更新、删除规则,动态的创建会话用户的视图.用户通过访问接口LIBPQ连接到数据库,授权访问和操作自己的视图.在数据库一级对用户数据进行了隔离.     

数据集成中XML数据查询语义重写

查询重写是数据库研究的一个基本问题，它和查询优化，数据仓库，数据集成，语义缓存等数据库问题密切相关，为提高集成系统的查询效率，系统选择提交频率较高的XML查询物化为中间层视图，用户提交查询后，系统尽可能利用中间视图层中视图，而不是访问数据源来回答查询，这个问题实际可以归结为半结构化查询重写问题，考虑到中间视图层空间的有限性，已有视图应当尽可能回答更多的查询，传统查询重写方法有考虑半结构化数据之间的约束，而根据约束可以等价变换查询，从而提高中间视图层中的表达能力，提出了一种新的半结构化查询重写的方法，该方法在保证算法正确性和完备性的基础上，利用上半结构化数据中的约束，尤其是XML文件中的路径依赖，来增强中间层物化视图的表达能力，理论分析和初步原型实验证明方法的有效性。     

数据仓库中基于实体化辅助视图的视图增量维护

为了加快对大量数据的查询处理速度，通常在数据仓库以实视图方式存储数据，当基础数据发生变化时，这些实视图也必须随着更新，因而视图自维护和一致性维护成为数据仓库的重要问题。本文提出利用视图计算的中间结果创建辅助视图，在数据仓库中进行实体化，采用有效的增量维护算法计算实视图的精确变化，实现数据仓库视图自维护。     

A wavelet framework for adapting data cube views for OLAP

This article presents a method for adaptively representing multidimensional data cubes using wavelet view elements in order to more efficiently support data analysis and querying involving aggregations. The proposed method decomposes the data cubes into an indexed hierarchy of wavelet view elements. The view elements differ from traditional data cube cells in that they correspond to partial and residual aggregations of the data cube. The view elements provide highly granular building blocks for synthesizing the aggregated and range-aggregated views of the data cubes. We propose a strategy for selectively materializing alternative sets of view elements based on the patterns of access of views. We present a fast and optimal algorithm for selecting a non-expansive set of wavelet view elements that minimizes the average processing cost for supporting a population of queries of data cube views. We also present a greedy algorithm for allowing the selective materialization of a redundant set of view element sets which, for measured increases in storage capacity, further reduces processing costs. Experiments and analytic results show that the wavelet view element framework performs better in terms of lower processing and storage cost than previous methods that materialize and store redundant views for online analytical processing (OLAP).     

基于视图相关因子的多视图数据竞争聚类算法

针对现有的单视图数据竞争聚类算法无法高效处理多视图数据的问题,提出了基于视图相关因子的多视图数据竞争聚类算法。首先,为了描述不同视图之间的相关性定义了一种视图相关性因子;然后,将视图相关因子与谱方法关于拉普拉斯矩阵的目标函数最大化问题结合,建立一个联合目标函数,使得不同视图之间的信息相互影响,以充分利用多视图的信息。通过解决联合目标函数的优化问题,得到每个视图的优化嵌入矩阵;最后,将得到的优化嵌入矩阵用于数据竞争聚类算法中。在人工和真实数据集上的仿真实验结果表明,新算法比现有的数据竞争聚类算法具有更高的聚类性能。     

A View Based Analysis on Web Service Registries

Web services registries are a cornerstone for the emerging service-oriented architecture and constitute a critical resource for Web services. We systematically illustrate and evaluate current registries and compare different approaches regarding their architectures and data models in the context of two views: the human and Web service based views. We use these views to show the different requirements and to illustrate the different abstractions when comparing Web service registries. The human view on Web service registry architectures is illustrated with the help of a case study. The Web service view on Web services registry architectures is illustrated from a software-service point of view. The data model of Web service registries is described in detail from a machine based view. The corresponding human view is described from an abstract level. Web service publishing and discovery are compared from a human and a Web service based view. Finally, we present a working example that uses our methodology to compare different Web service registries and to explain the different views introduced in this paper. Recommended by: Dimitrios Georgakopoulos     

Updating Recursive XML Views of Relations

This paper investigates the view update problem for XML views published from relational data.We consider XML views defined in terms of mappings directed by possibly reeursive DTDs compressed into DAGs and stored in relations. We provide new techniques to efficiently support XML view updates specified in terms of XPath expressions with recursion and complex filters.The interaction between XPath recursion and DAG compression of XML views makes the analysis of the XML view update problem rather intriguing.Furthermore,many issues are still open even for relational view updates, and need to be explored.In response to these,on the XML side,we revise the notion of side effects and update semantics based on the semantics of XML views,and present efficient algorithms to translate XML updates to relational view updates. On the relational side,we propose a mild condition on SPJ views,and show that under this condition the analysis of deletions on relational views becomes PTIME while the insertion analysis is NP-complete.We develop an efficient algorithm to process relational view deletions,and a heuristic algorithm to handle view insertions.Finally,we present an experimental study to verify the effectiveness of our techniques.     

View adaptation in the fragment-based approach

View adaptation relies on adapting a set of materialized views in response to schema changes of source relations and/or after view redefinition. Recently, several view selection methods that are based on materializing fragments of the view rather than the whole view have been proposed. We call this approach the fragment-based approach. This paper presents a view adaptation method in the fragment-based approach, which is aimed at exploiting the opportunities to share not only materialized data, but also computation between the different views. In order to do this, the views are modeled using the so-called multiview materialization graph, which represents the views as a bipartite directed acyclic graph whose nodes are operations and fragments of the views. Then, the adaptation is performed regarding all materialized views and not solely the old materialization of the view. However, the data independence is preserved for the views that are not affected by the change. On the contrary, in related work, the adaptation technique is based solely on the old materialization of the same view. We studied the impact of the fragmentation on the adaptation techniques and showed the advantages and drawbacks of this approach.     

数据仓库多视图的并发控制分析

对传统的２ＰＬ协议冲突操作概念加以扩展,本文提出用依赖图方法判断数据仓库实例化视图调度是可串行化．数据仓库的不同实例化视图访问同一数据源时,这些视图之间的一致性可能得不到保证．本文设计了多视图一致性算法－画笔算法．该算法具有简单性和可扩展性．     

A formal perspective on the view selection problem

The view selection problem is to choose a set of views to materialize over a database schema, such that the cost of evaluating a set of workload queries is minimized and such that the views fit into a prespecified storage constraint. The two main applications of the view selection problem are materializing views in a database to speed up query processing, and selecting views to materialize in a data warehouse to answer decision support queries. In addition, view selection is a core problem for intelligent data placement over a wide-area network for data integration applications and data management for ubiquitous computing. We describe several fundamental results concerning the view selection problem. We consider the problem for views and workloads that consist of equality-selection, project and join queries, and show that the complexity of the problem depends crucially on the quality of the estimates that a query optimizer has on the size of the views it is considering to materialize. When a query optimizer has good estimates of the sizes of the views, we show a somewhat surprising result, namely, that an optimal choice of views may involve a number of views that is exponential in the size of the database schema. On the other hand, when an optimizer uses standard estimation heuristics, we show that the number of necessary views and the expression size of each view are polynomially bounded. Received: November 20, 1001 / Accepted: May 30, 2002 / Published online: September 25, 2002     

iViewer:利用数据服务即时生成跨域数据视图

越来越多的企业和组织选择通过广域、开放的互联网作为其协作平台,业务决策者往往需要即时汇聚并综合分析来自多个部门的资源信息以进行临机决策。如何即时构建满足用户需求的跨组织数据视图,动态维护视图和数据源之间的一致性是需要求解的一个关键问题。提出了一种互联网环境下跨组织业务数据视图的动态生成方法iViewer,利用数据服务来封装自治、异构和动态变化的数据源;通过可视化和易用的数据服务组合操作来动态构建数据视图;提出了一种基于轮询的视图动态更新算法,维护数据源和数据视图的一致性,从而使得数据视图能够随数据源的变化而自主变化;详述了iViewer方法的原理和过程,并通过一个火灾应急处置场景中,面向指挥中心的跨部门火灾救援设备数据视图的动态生成过程例证了iViewer方法的效果。     

Selection of views to materialize in a data warehouse

A data warehouse stores materialized views of data from one or more sources, with the purpose of efficiently implementing decision-support or OLAP queries. One of the most important decisions in designing a data warehouse is the selection of materialized views to be maintained at the warehouse. The goal is to select an appropriate set of views that minimizes total query response time and the cost of maintaining the selected views, given a limited amount of resource, e.g., materialization time, storage space, etc. In This work, we have developed a theoretical framework for the general problem of selection of views in a data warehouse. We present polynomial-time heuristics for a selection of views to optimize total query response time under a disk-space constraint, for some important special cases of the general data warehouse scenario, viz.: 1) an AND view graph, where each query/view has a unique evaluation, e.g., when a multiple-query optimizer can be used to general a global evaluation plan for the queries, and 2) an OR view graph, in which any view can be computed from any one of its related views, e.g., data cubes. We present proofs showing that the algorithms are guaranteed to provide a solution that is fairly close to (within a constant factor ratio of) the optimal solution. We extend our heuristic to the general AND-OR view graphs. Finally, we address in detail the view-selection problem under the maintenance cost constraint and present provably competitive heuristics.