分布式数据库查询优化处理——基于关系代数等价变换的查询优化处理

在进行分布式数据库应用时，快速而准确的得到查询结果一直是分布式数据库得以应用的关键问题。本文阐述了分布式查询优化的一种策略和算法——基于关系代数等价变换的查询优化处理。     

基于分布式数据库的查询优化技术及应用

分布式数据库系统的分布和冗余使查询处理复杂化,因此分布式查询处理的优化显得尤为重要。本文结合自己实践经验,从查询策略选择的角度讨论了查询优化技巧,重点介绍了基于关系代数等价变换的优化算法和半联接的查询技术及其应用。     

基于关系代数的分布式数据库查询优化

分布式数据库系统由于其数据的物理分布和冗余特性,使得对于分布式数据库的查询优化处理难度更大和复杂度更高,而分布式数据库查询优化处理一直是分布式数据库主要研究问题之一。本文主要概括地介绍分布式数据库查询过程、查询优化的策略和目标,重点阐述了基于关系代数等价变换的分布式数据库查询优化算法。     

分布式数据库系统中的查询优化处理

分布式查询处理是用户与分布式数据库的接口,也是分布式数据库研究的主要问题之一。在分布式查询处理中基于不同的目标有不同的查询优化算法,文章主要讨论基于最小传输代价原则的半连接算法,分析了半连接算法的原理并给出了多关系半连接查询优化算法思考。     

分布式数据库查询优化策略研究

分布式数据库系统由于数据的分布和冗余使得分布式查询处理增加了许多新的内容和复杂性,因此分布式查询处理的优化显得尤为重要。本文简要介绍分布式查询优化的目标、策略,并针对分布式数据库系统的查询优化,讲述三个典型的算法:INGRES算法、SystemR*算法、SDD-1算法,并进行对比、优化、总结,最后对SDD-1算法进行改进。     

分布式数据库中的数据分布

本文讨论了分布式系统中的数据分布问题,给出了数据分布的一些基本方法,并对关系分布式数据库中的查询优化问题进行了讨论,说明了查询分解在减少查询的响应时间和处理代价中的重要作用。同时,给出了分布式查询优化的三个较有效的算法,并对每一个算法作出了简单的评价。在第一节中,给出了分布式查询的一个例子,它说明了分布式查询的复杂性。第二节讨论关系分割的一些基本方法,包括对关系的水平分割、垂直分割和水平垂直分割。分布式查询优化算法以及最优查询优化算法所应具有的性质在第三节给出。最后是结语。     

基于分布式数据库的查询处理和优化算法

分布式查询处理和优化是用户与分布式数据库的接口,也是分布式数据库研究的主要问题之一。分布式数据库中数据的数据分散存放和冗余使得查询处理和优化更加复杂。文章分析了分布式查询处理过程．重点阐述了优化的各种策略和算法,分析了优缺点并给出了算法选择的方法。     

基于分布式操作系统的数据灾备与拓扑连接挖掘方法

在传统的分布式操作系统灾备处理过程的基础上,结合已有分布式跨边界片段连接优化方法,提出基于空间片段拓扑连接优化的关系代数转换原则,通过利用等价转换规则,进一步简化经过数据本地化处理后的查询树。然后引入连接归并树和执行计划树等概念,并利用相应归并和优化算法将全局空间查询转化为各个场地局部空间数据库的具体执行计划。     

分布式数据库查询处理和优化算法

随着大数据时代的到来和云服务的发展,分布式数据库系统(DDBS)的应用越来越普遍化,分布式数据库系统是通过分布式查询处理与分布式数据库(DDB)交互的综合性应用。无论是集中式数据库系统,还是分布式数据库。数据的查询处理都贯穿于整个应用项目的始终,而查询处理的优化也就显得非常重要。分布式数据库的数据具有分布性和冗余度的特点。这样在处理查询优化时一些技术的实现和问题的思考就相对复杂。本文从分布式数据库查询处理基本原理出发,对各优化策略和算法进行了阐述,并且针对性的提出了各个算法选择的思路和途径。     

基于XML的关系代数实现研究

提出了在XML说明描述语言中实现关系代数操作的方法.关系代数表达式可以用若干个XML子句描述,并通过等价变换得到查询结果.该方法为查询XML数据提供了一种简洁、有效的手段.     

Fuzzy database query languages and their relational completenesstheorem

Two fuzzy database query languages are proposed. They are used to query fuzzy databases that are enhanced from relational databases in such a way that fuzzy sets are allowed in both attribute values and truth values. A fuzzy calculus query language is constructed based on the relational calculus, and a fuzzy algebra query language is also constructed based on the relational algebra. In addition, a fuzzy relational completeness theorem such that the languages have equivalent expressive power is proved     

Querying fuzzy relational databases through fuzzy domain calculus

In this paper we present a definition of a domain relational calculus for fuzzy relational databases using the GEFRED model as a starting point. It is possible to define an equivalent fuzzy tuple relational calculus and consequently we achieve the two query language levels that Codd designed for relational databases but these are extended to fuzzy relational databases: Fuzzy relational algebra (defined in the GEFRED model) and the fuzzy relational calculus which is put forward in this paper. The expressive power of this fuzzy relational calculus is demonstrated through the use of a method to translate any algebraic expression into an equivalent expression in fuzzy domain relational calculus. Furthermore, we include a useful system so that the degree to which each value has satisfied the query condition can be measured. Some examples are also included in order to clarify the definition. ©1999 John Wiley & Sons, Inc.     

SPARQL查询的关系代数表示与转换方法

为解决基于本体的数据集成系统中的查询转换问题,提出SPARQL查询的关系代数表示和转换方法。引入RDF图模式的关系代数,定义了五种基本的关系运算,给出了SPARQL查询的关系代数表示;提出了SPARQL到SQL的查询转换方法,将基于本体的SPARQL查询转换为可在关系数据库上直接执行的SQL查询,从而实现关系数据库的集成。系统实现表明,该方法能够有效地实现查询语言的转换。     

A foundation for conventional and temporal query optimizationaddressing duplicates and ordering

Most real-world databases contain substantial amounts of time-referenced, or temporal, data. Recent advances in temporal query languages show that such database applications may benefit substantially from built-in temporal support in the DBMS. To achieve this, temporal query representation, optimization, and processing mechanisms must be provided. This paper presents a foundation for query optimization that integrates conventional and temporal query optimization and is suitable for both conventional DBMS architectures and ones where the temporal support is obtained via a layer on top of a conventional DBMS. This foundation captures duplicates and ordering for all queries, as well as coalescing for temporal queries, thus generalizing all existing approaches known to the authors. It includes a temporally extended relational algebra to which SQL and temporal SQL queries may be mapped, six types of algebraic equivalences, concrete query transformation rules that obey different equivalences, a procedure for determining which types of transformation rules are applicable for optimizing a query, and a query plan enumeration algorithm     

基于递归和表函数的一到多数据转换研究

针对关系表达式难以进行无限制一到多数据转换的问题,通过关系代数的扩展表达一到多数据转换,采用递归查询和表函数实现无限制一到多数据转换,在每个输入元组上产生一个或者多个输出元组。递归查询通过创建初始结果,递归获取结果集,并返回最终结果集;表函数声明变量集合,使用过程体和游标循环访问表,迭代输出元组。实验分析不同参数影响因素下有限制和无限制转换的不同方法,结果表明扩展方法能够改善系统性能。     

Foundations for object-oriented query processing

A minimal framework for an object-oriented query language standard should (1) include a formal definition of a high-level data model and the syntax and semantics of associated query languages, (2) provide the functionality of relational query languages, and (3) support proofs of correctness of transformations for logical query optimization. In this paper, a high-level conceptual model for object-oriented query processing is discussed; the model includes widely-used structural abstractions such as the isa relationship, associations (properties) between complex objects and complex objects/values, and inheritance of properties. A formal, algebraic query language for the model, inspired by relational algebra, is presented. Operators of the algebra allow queries based on values, queries that manipulate entire objects, and queries that construct new objects from existing objects/values. All queries retain connections to existing database objects, providing logical access paths to data. Each query result is a class, so the algebra has the closure property. The intensional and extensional results of query operators are summarized. Two forms of logical query optimization supported by the query algebra are outlined: algebraic transformations and classifier-based optimizations (optimizations which employ inclusion and exclusion dependencies between classes).     

Relational completeness of query languages for annotated databases

Annotated relational databases can be queried either by simply making the annotations explicitly available along the ordinary data, or by adapting the standard query operators so that they have an implicit effect also on the annotations. We compare the expressive power of these two approaches. As a formal model for the implicit approach we propose the color algebra, an adaptation of the relational algebra to deal with the annotations. We show that the color algebra is relationally complete: it is equivalent to the relational algebra on the explicit annotations. Our result extends a similar completeness result established for the query algebra of the MONDRIAN annotation system, from unions of conjunctive queries to the full relational algebra. We also show that the color algebra is nonredundant: no operator can be expressed in terms of the other operators. We also present a generalization of the color algebra that is relationally complete in the presence of built-in predicates on the annotations.     

基于关系代数的XML数据查询

XML渐已成为Web上数据表示和交换的通用语言。为了有效地利用大量的XML文档，需要研究XML数据查询技术。提出了基于关系代数的XML数据查询方法。XML子句可以用关系代数表达式表示，并通过关系代数操作得到查询结果。该方法为查询XML数据提供了一种简洁和有效的手段。