XQuery的实现机制

随着越来越多的数据用XML来表示,交换和查询XML数据的能力变得日益重要。XQuery是W3C提出的XML查询语言,很有希望成为以后的XML查询语言标准。文章讨论XQuery的实现机制及其优化。     

XQuery实现技术研究综述

XML数据的广泛应用,使得高性能的XQuery实现成为XML数据处理领域的重要课题,但XQuery的灵活性和复杂性为其实现技术研究提出了巨大挑战。XQuery语言的高性能实现需要利用XML查询代数提供的查询优化方法,也需要采取高效的树模式整体匹配算法。给出了XQuery语言实现的基础架构,探讨了原生XML数据库系统中XQuery实现的关键技术——查询代数和树模式查询的国内外研究现状,展望了未来的研究方向及面临的挑战。     

一种XML文档更新操作的实现

文章描述了一种XML文档更新操作的设计和实现方法。对XML文档查询语言Xquery进行扩展，增加XML文档的更新功能，并且在Kweelt系统的基础上实现了XML文档的更新操作。测试表明该方法对XML文档的更新效率有明显的提高。     

支持XML查询代数和树模式查询的XQuery系统框架

XQuery语言的高性能实现需要利用XML查询代数提供的查询优化方法,也需要采取高效的树模式整体匹配算法。为了将这两种XML查询处理技术有效地结合在XQuery语言处理系统中,提出了一种通用系统框架来支持XQuery语言的高性能实现。在这个框架内,提供开放式XML数据源连接,并且通过作为中间语言的一种函数式查询计划描述语言FXQL来支持各种查询代数算子和树查询模式的表示,既允许采用各种XML查询代数,又允许采用各种树模式查询算法;进而,通过这种中间层的程序变换可以实现基于各种查询代数的查询重写,并从查询计划中分离出独立的树模式查询计算,使两种查询处理技术适当地统一在同一系统框架中,有效地支持了多种环境下XQuery语言的实现。     

一种基于树状逻辑式的XML查询方法*

随着XML在各类数据表示中的广泛应用,XML文档的查询方法成为当前数据处理的一个重要问题。已有的研究如XPath和XQuery得到应用,但其查询表现存在一些缺点需要改进。从模板匹配的角度出发,基于谓词逻辑设计了树状逻辑表达式LXT。该表达式的特点是能以树状结构模板描述XML文档查询需求。在此基础上,进一步探讨了基于LXT表达式的XML文档查询方法,从数据的查询过滤、结果的组织构造与含义等方面描述了利用LXT的特点设计XML查询表现形式的基本思路。     

XQuery的应用分析

XML查询语言XQuery是导航语言XPath的扩展,它是一种语法简单灵活且表现力强大的功能性语言。XQuery与XML数据结构有内在的联系,可以方便地编写业务逻辑,并且本质上就可以操作XML数据。本文对XQuery发展状况的进行了概要介绍,通过查询语言XQuery的主要概念,及XQuery语言在数据查询、转换等方面的应用分析,对XML文档查询语言的实际应用情况作出讨论。     

XQuery的应用分析

XML查询语言XQuery是导航语言XPath的扩展,它是一种语法简单灵活且表现力强大的功能性语言。XQuery与XML数据结构有内在的联系,可以方便地编写业务逻辑,并且本质上就可以操作XML数据。本文对XQuery发展状况的进行了概要介绍,通过查询语言XQuery的主要概念,及XQuery语言在数据查询、转换等方面的应用分析,对XML文档查询语言的实际应用情况作出讨论。     

XQuery语言查询优化策略研究

XQuery查询语言在XPath路径查询的基础上使用FLWR等表达式实现XML数据的复杂查询或重构。查询优化是查询处理中重要的组成部分。文章提出了两个优化策略：路径的关联优化和FLWOR查询的重写,XMark实验表明能有效提高XQuery查询的执行效率。     

基于关系数据库有效地实现RPE查询

各种XML查询语言的共同特点就是利用正则路径表达式(RPE)来导航XML文档的查询。本文结合我们提出的一种新的XML数据的关系存储模式，对有效地实现RPE查询的相关研究工作进行了总结，并提出了两个有效地实现包含连接的索引改进归并连接算法。算法采用索引定位技术、短路技术和预侦技术来减少连接代价。因此，不仅能够在当前上下文计算环境下有效地实现包含连接的计算，而且能够大量地避免包含连接中不必要的扫描和搜索。     

Developing an efficient query system for encrypted XML documents

XQuery is a query and functional programming language that is designed for querying the data in XML documents. This paper addresses how to efficiently query encrypted XML documents using XQuery, with the key point being how to eliminate redundant decryption so as to accelerate the querying process. We propose a processing model that can automatically translate the XQuery statements for encrypted XML documents. The implementation and experimental results demonstrate the practicality of the proposed model.     

XML数据查询语言XQuery应用分析

目前,XML已经成为事实上的数据表示和数据交换标准,XQuery是用来对XML文档进行数据查询的W3C候选推荐标准。结合XQuery规范的最新发展状况,介绍XQuery查询语言的主要特性,通过实例讨论XQuery语言在数据查询、转换等方面的应用。对SQL/XML和Xquery进行了比较,并分析了XQuery的实现与应用情况。     

支持全文检索的XQuery查询处理及优化的研究

XQuery作为由W3C组织提出的一种XML查询语言,正在成为当前应用于XML数据库中对XML数据操作的一个规范。为了提高对XML中文本内容的查询支持,W3C又进一步设计了支持全文检索功能的语法规范。针对最新的XQuery及全文检索语法特征,文章提出了支持全文检索功能XQuery的解析与查询执行策略,为XQuery的查询处理提供解决方案。在此基础上,针对全文检索功能的查询执行计划,提出了适用于窗口查询,距离查询,是否排序查询的优化方案,以减少查询执行的代价,提高XQuery查询的效率。     

Declarative XML Update Language Based on a Higher Data Model

With the extensive use of XML in applications over the Web, how to update XML data is becoming an important issue because the role of XML has expanded beyond traditional applications in which XML is used for information exchange and data representation over the Web. So far, several languages have been proposed for updating XML data, but they are all based on lower, so-called graph-based or tree-based data models. Update requests are thus expressed in a nonintuitive and unnatural way and update statements are too complicated to comprehend. This paper presents a novel declarative XML update language which is an extension of the XML-RL query language. Compared with other existing XML update languages, it has the following features. First, it is the only XML data manipulation language based on a higher data model. Second, this language can express complex update requests at multiple levels in a hierarchy in a simple and flat way. Third, this language directly supports the functionality of updating complex objects while all other update languages do not support these operations. Lastly, most of existing languages use rename to modify attribute and element names, which is a different way from updates on value. The proposed language modifies tag names, values, and objects in a unified way by the introduction of three kinds of logical binding variables: object variables, value variables, and name variables.     

带Order子句的XQuery在XML流上的查询实现

随着XML的广泛应用,使得作为XML文档查询语言的XQuery成为人们研究的热点问题.将复杂XQuery在XML数据流上的查询应用于服务器/客户端模式来满足高效、实时查询的要求,所实现的XQuery查询原型系统XSIEQ支持嵌套、order子句的多关键字排序等.一次典型的XQuery查询过程可分为XPath查询、查询后处理两个阶段,本文着重描述查询后处理过程,最后给出了XSIEQ和Qizx在查询后处理时间性能上的对比及分析.     

A survey on XML streaming evaluation techniques

XML is currently the most popular format for exchanging and representing data on the web. It is used in various applications and for different types of data including structured, semistructured, and unstructured heterogeneous data types. During the period, XML was establishing itself, data streaming applications have gained increased attention and importance. Because of these developments, the querying and efficient processing of XML streams has became a central issue. In this study, we survey the state of the art in XML streaming evaluation techniques. We focus on both the streaming evaluation of XPath expressions and of XQuery queries. We classify the XPath streaming evaluation approaches according to the main data structure used for the evaluation into three categories: automaton-based approach, array-based approach, and stack-based approach. We review, analyze, and compare the major techniques proposed for each approach. We also review multiple query streaming evaluation techniques. For the XQuery streaming evaluation problem, we identify and discuss four processing paradigms adopted by the existing XQuery stream query engines: the transducer-based paradigm, the algebra-based paradigm, the automata-algebra paradigm, and the pull-based paradigm. In addition, we review optimization techniques for XQuery streaming evaluation. We address the problem of optimizing XQuery streaming evaluation as a buffer optimization problem. For all techniques discussed, we describe the research issues and the proposed algorithms and we compare them with other relevant suggested techniques.     

基于扩展XQuery引擎的空间数据流查询方法研究

针对目前XML数据流处理中通常采用的查询语言XPath和XQuery均不支持空间运算,无法应用到空间数据流处理技术中的问题,设计了一种通过扩展现有商业化XQuery引擎功能基础上的空间数据流检索方法。     

基于XQuery的数据集成系统中的查询分解算法

XQucry查询语言使用XML作为抽象数据模型。可以对基于XML的数据源作查询，无论这些数据源是真正的XML文件或者是中间件提供的XML视图。本文研究了以XQuery作为查询语言的数据集成系统中的查询分解算法。在XQucry语言的层次，利用它的语言特点实现了多数据源的查询分解算法。     

A comparison of two approaches to utilizing XML in parametric databases for temporal data

The parametric data model captures an object in terms of a single tuple. This feature eliminates unnecessary self-join operations to combine tuples scattered in a temporal relation. Despite this advantage, this model is relatively difficult to implement on top of relational databases because the sizes of attributes are unfixed. Since data boundaries are not problematic in XML, XML can be an elegant solution to implement parametric databases for temporal data. There are two approaches to implementing parametric databases using XML: (1) a native XML database with XQuery engine, and (2) an XML storage with a temporal query language. To determine which approach is appropriate in parametric databases, we consider four questions: the effectiveness of XML in modeling temporal data, the applicability of XML query languages, the user-friendliness of the query languages, and system performances of two approaches. By evaluating the four questions, we show that the latter approach is more appropriate to utilizing XML in parametric databases.     

XQBE: A Graphical Environment to Query XML Data

XQuery, the standard query language for XML, is increasingly popular among computer scientists with SQL background, since XQuery and SQL require comparable skills. However, these experts are limited in number, and the availability of easier XQuery “dialects” could be extremely valuable. With this motivation in mind, we designed XQBE, a visual dialect of XQuery inspired by the QBE language (Query by Example). Coherent with the hierarchical nature of XML, XQBE uses one or more hierarchical structures to denote the input documents and one structure to denote the document produced in output. These structures are annotated to express selection predicates; explicit binding edges connecting the nodes of these structures visualize the input/output mappings. This paper presents XQBE through several examples and describes the main features of our implementation of the language, a visual editor coupled with an XQBE-to-XQuery translator. Indeed, the XQBE front-end is a general purpose user-friendly visual query interface, capable of providing access to any data storage system that exposes XQuery APIs. Available schema information can be exploited to guide users in querying data sets they are not familiar with. Also, switching between the visual and textual versions of the same query could be helpful for XQuery learners.     

XML data mining

With the spreading of XML sources, mining XML data can be an important objective in the near future. This paper presents a project focussed on designing a general‐purpose query language in support of mining XML data. In our framework, raw data, mining models and domain knowledge are represented by way of XML documents and stored inside native XML databases. Data mining (DM) tasks are expressed in an extension of XQuery. Special attention is given to the frequent pattern discovery problem, and a way of exploiting domain‐dependent optimizations and efficient data structures as deeper as possible in the extraction process is presented. We report the results of a first bunch of experiments, showing that a good trade‐off between expressiveness and efficiency in XML DM is not a chimera. Copyright © 2009 John Wiley & Sons, Ltd.