Query generation for retrieving data from distributed semistructured documents using a metadata interface

We describe a method for generating queries for retrieving data from distributed heterogeneous semistructured documents, and its implementation in the metadata interface DDXMI (distributed document XML metadata interchange). The proposed system generates local queries appropriate to local schemas from a user query over the global schema. The system constructs mappings between global schema and local schemas (extracted from local documents if not given), path substitution, and node identification for resolving the heterogeneity among nodes with the same label that often exist in semistructured data. The system uses Quilt as its XML query language. An experiment is reported over three local semistructured documents: ‘thesis’, ‘reports’, and ‘journal’ documents with ‘article’ global schema. The prototype was developed under Windows system with Java and JavaCC.     

XML Schema与DTD的比较及应用

XML是目前广泛应用的数据交换标准，而模式是应用XML进行数据交换的正确性的保证机制之一。模式详细描述了文档的结构，确保文档的元素和属性等的正确性。XML Schema和DTD是其中应用最广泛的模式。文中详细比较了两者的异同，并指出了各自的局限及最佳的应用，DTD非常适合于文本密集型XML文档，而XML Schema更适合于数据密集型XML文档。     

Rewriting of visibly pushdown languages for XML data integration

In this work, we focus on XML data integration by studying rewritings of XML target schemas in terms of source schemas. Rewriting is very important in data integration systems where the system is asked to find and assemble XML documents from the data sources and produce documents that satisfy a target schema.As schema representation, we consider Visibly Pushdown Automata (VPAs), which accept Visibly Pushdown Languages (VPLs). The latter have been shown to coincide with the family of (word-encoded) regular tree languages, which are the basis of formalisms for specifying XML schemas. Furthermore, practical semi-formal XML schema specifications (defined by simple pattern conditions on XML) compile into VPAs that are exponentially more concise than other representations based on tree automata.Notably, VPLs enjoy a “well-behavedness” that facilitates us in addressing rewriting problems for XML data integration. Based on VPAs, we positively solve these problems, and present detailed complexity analyses.     

保持数据约束的关系数据库至XML文档的转换

XML已成为Internet上的技术趋势,在保留原有关系数据库的同时发展XML文档是目前的最佳选择,它需要在保持数据依赖约束基础上实现关系数据库与XML文档的转换.这一过程中,模式转换必须先于数据转换,因为现有的关系数据库通常是规范化的,重建XML文档树结构才能实现这一转换.为了达成此目的,首先依据已有的数据依赖约束将规范化的关系联合进一组表格,实现反向规范化,然后将这些联合表格映射为一组DOM,归并成XML文档树,根据用户选择的根结点,以及与它相连的结点形成一个期望的局部文档树,被选的XML文档树又映射为DTD格式的XML模式.这样就可以将联合表映射成一组DOM,并将其归并成单一DOM,最终转换成XML文档.     

生成具有层次特征XML模式的简化算法

XML已经广泛地应用于数据描述及数据交换,然而日常数据的大部分依旧存放在关系型数据库里,因此转换关系数据到XML文档的需求日益增长,如何高效生成用户满意的XML模式是其中的关键。NeT&CoT算法2是近年来提出的可根据给定的关系模式生成具有层次特征的XML的自动转换算法,然而它存在效率不高的问题。因此,该文在NeT&CoT算法的基础上提出了简化算法,通过引入四个简化性质,避免了费时的nest操作,提高了转换效率。     

基于关系数据库分裂存储的XML文档片段重构*

首先对基于关系数据库分裂存储XML文档的各种方法进行总结,并对X-RESTORE基于关系数据库的XML文档的分裂存储原理和关系存储模式进行介绍;然后对XML查询的三种计算模式进行分析;最后基于X-RESTORE给出一个重构结果文档片段的算法,并对该算法的执行代价进行分析。分析结果显示,X-RESTORE不仅能够有效地支持XML的选择计算模式,而且能够有效地支持XML的抽取计算模式和重构计算模式。     

抽取XML文档到关系数据库

XML在关系数据库中的存储问题是XML研究领域中的一个重要问题。在总结多种映射方法的基础上,提出了一种方法将多个相似的XML文档进行解析,根据映射关系,生成各自的关系模式,并分析归纳出一个集成的关系模式,然后创建一个关系数据库,并在映射关系的基础上提取并存储XML文档数据到关系数据库。此方法以较为简洁的结构保存了XML文档的数据信息,其最大的特点就是不用考虑文档的模式信息（DTD,XML Schema）。并通过一个具体的实验结果来说明这种方法的有效性。     

XML文档架构与关系数据模型间的映射研究

XML逐渐成为Internet上数据描述和交换的标准。随着Web上大量数据用XML文档表示出来,有必要对这些XML文档进行操纵管理。为了结合关系数据库系统强大的数据操纵能力,论文在对XML文档的逻辑结构进行简要介绍的基础上,就XML文档特别是结构化XML文档与关系数据模型数据之间的互动映射作了深入探讨,特别是在数据结构和数据完整性约束条件的映射关系上作了更深一层的研究,提出了一系列基于XML本身的映射规则。     

基于语义约束的数据转换模式研究

XML是因特网中不同企业之间进行信息交流的一种标准的数据转换模式,为了加速数据之间的转换,企业组织通过定义公共数据文档接口来实现基于XML的应用。本文提出了一种新的将关系数据模式转换为XML模式的方法。在转换的过程中,不仅考虑关系模式的结构,而且考虑语义约束,比如内部函数依赖。该方法的输入模式是具有多值函数依赖的关系模式,输出模式是X-Schema。最后,通过实验对该转换方法进行了验证。     

基于DOM的XML文档到关系数据库的数据转换方法

随着Internet的普及和Web技术的快速发展,XML正迅速成为事实上的数据表示和交换标准,大量XML数据的涌现出来,为了实现XML数据的快速查询和有效的数据交换,需要将XML文档数据转存到关系数据库中。该文介绍了基于DOM的XML文档到关系数据库的数据转换方法。     

XML文档在关系数据库中的存储方法

XML是网络中跨平台数据发布与交换的标准格式,它在数据库领域有着广阔的应用空间,然而XML文档的树型结构与关系数据库的二维表结构之间存在着巨大的差异,因此在关系数据库中存储XML文档需要进行一些特殊处理。本文分析了XML文件在数据库领域中的存储与管理方法,并重点就Oracle9i中XML相关技术在现代远程教育中的应用进行了讨论,针对以数据为中心和以文档为中心两类文档资料的存储给出了可行的存储方案。     

Storing XML (with XSD) in SQL databases: interplay of logical and physical designs

Much of business XML data has accompanying XSD specifications. In many scenarios "shredding" such XML data into a relational storage is a popular paradigm. Optimizing evaluation of XPath queries overmuch XML data requires paying careful attention to both the logical and physical designs of the relational database where XML data is shredded. None of the existing solutions has taken into account physical design of the generated relational database. In this paper, we study the interplay of logical and physical design and conclude that 1) solving them independently leads to suboptimal performance and 2) there is substantial overlap between logical and physical designs: some well-known logical design transformations generate the same mappings as physical design. Furthermore, existing search algorithms are inefficient to search the extremely large space of logical and physical design combinations. We propose a search algorithm that carefully avoids searching duplicated mappings and utilizes the workload information to further prune the search space. Experimental results confirm the effectiveness of our approach.     

An XML-Based Approach to Publishing and Querying the History of Databases

There is much current interest in publishing and viewing databases as XML documents. The general benefits of this approach follow from the popularity of XML and the tool set available for visualizing and processing information encoded in this universal standard. In this paper, we explore the additional and unique benefits achieved by this approach on temporal database applications. We show that XML with XQuery can provide surprisingly effective solutions to the problem of supporting historical queries on past content of database relations and their evolution. Indeed, using XML, the histories of database relations can be naturally represented by temporally grouped data models. Thus, we identify mappings from relations to XML that are most conducive to modeling and querying database histories, and show that temporal queries that would be difficult to express in SQL can be easily expressed in standard XQuery. This approach is very general, insofar as it can be used to store the version history of arbitrary documents and, for relational databases, it also supports queries on the evolution of their schema. Then, we turn to the problem of supporting efficiently the storage and the querying of relational table histories. We present an experimental study of the pros and cons of using native XML databases, versus using traditional databases, where the XML-represented histories are supported as views on the historical tables.     

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。     

Mapping DTDs to relational schemas with semantic constraints

XML is becoming a prevalent format and standard for data exchange in many applications. With the increase of XML data, there is an urgent need to research some efficient methods to store and manage XML data. As relational databases are the primary choices for this purpose considering their data management power, it is necessary to research the problem of mapping XML schemas to relational schemas. The semantics of XML schemas are crucial to design, query, and store XML documents and functional dependencies are very important representations of semantic information of XML schemas. As DTDs are one of the most frequently used schemas for XML documents in these days, we will use DTDs as schemas of XML documents here. This paper proposes the concept and the formal definition of XML functional dependencies over DTDs. A method to map XML DTDs to relational schemas with constraints such as functional dependencies, domain constraints, choice constraints, reference constraints, and cardinality constraints over DTDs is given, which can preserve the structures of DTDs as well as the semantics implied by the above constraints over DTDs. The concepts and method of mapping DTDs to relational schemas presented in the paper can be extended to the field of XML Schema just with some modifications in related formal definitions.     

基于编码的XML关系数据库存储

在XML的发展过程中,如何有效地利用关系数据库技术存储和查询XML数据已经成为一个研究热点．提出了一种基于前、后序编码的XML关系数据库存储方法,该方法采用的模式映射方法能够使基于不同DTD（或schema）的XML文档保存在同一个关系表中,支持快速的XML路径查询,且具有较高的XML文档重组效率．对该方法中递归模式的处理技术也进行了讨论．实验表明,与XRel,Florescu和Kossman等人提出的XML关系数据库存储方法相比,该方法能够缩短复杂XML路径查询（如带条件谓词约束的路径查询）的响应时间．     

Designing XML documents from conceptual schemas and workload information

Due to the increase of XML-based applications, XML schema design has become an important task. One approach is to consider conceptual schemas as a basis for generating XML documents compliant to consensual information of specific domains. However, the conversion of conceptual schemas to XML schemas is not a straightforward process and inconvenient design decisions can lead to a poor query processing on XML documents generated. This paper presents a conversion approach which considers data and query workload estimated for XML applications, in order to generate an XML schema from a conceptual schema. Load information is used to produce XML schemas which can respond well to the main queries of an XML application. We evaluate our approach through a case study carried out on a native XML database. The experimental results demonstrate that the XML schemas generated by our methodology contribute to a better query performance than related approaches.

Authorization Translation for XML Document Transformation

XML access control models proposed in the literature enforce access restrictions directly on the structure and content of an XML document. Therefore access authorization rules (authorizations, for short), which specify access rights of users on information within an XML document, must be revised if they do not match with changed structure of the XML document. In this paper, we present two authorization translation problems. The first is a problem of translating instance-level authorizations for an XML document. The second is a problem of translating schema-level authorizations for a collection of XML documents conforming to a DTD. For the first problem, we propose an algorithm that translates instance-level authorizations of a source XML document into those for a transformed XML document by using instance-tree mapping from the transformed document instance to the source document instance. For the second problem, we propose an algorithm that translates value-independent schema-level authorizations of non-recursive source DTD into those for a non-recursive target DTD by using schema-tree mapping from the target DTD to the source DTD. The goal of authorization translation is to preserve authorization equivalence at instance node level of the source document. The XML access control models use path expressions of XPath to locate data in XML documents. We define property of the path expressions (called node-reducible path expressions) that we can transform schema-level authorizations of value-independent type by schema-tree mapping. To compute authorizations on instances of schema elements of the target DTD, we need to identify the schema elements whose instances are located by a node-reducible path expression of a value-independent schema-level authorization. We give an algorithm that carries out path fragment containment test to identify the schema elements whose instances are located by a node-reducible path expression.     

一个从关系数据模型到XML文档的翻译器设计

XML技术与关系数据模型的关系非常密切,将关系数据库中的数据转换为XML文档格式有着重要的现实意义,本文介绍了利用OmniMark语言开发一个从关系数据模型到XML文档翻译器的方法,重点分析了关系模式、DTD与XMLSchemas,跨平台无关性,SGML语法检查等关键技术。     

基于模式的XML文档在关系数据库中存储的设计

随着XML逐渐成为因特网上数据表示和数据交换的新标准,基于XML的数据交换数量呈现出指数增长的趋势。为了解决XML数据的存储问题,详细分析了XML模式,提出一个中间文法XSchema,建立中间数据模型XSModel来实现XML模式到关系模式的映射,并把这个映射从XML DTD推广到XML Schema。