一种基于XML Schema的映射算法

论文基于XML Schema规范,提出了一种等价于XML Schema的数据模型是New_Schema,并实现了从New_Schema到关系模式的映射算法。实验证明,在XML文档的模式信息比较稳定的情况下,New_Schema映射方法在数据转储过程中的信息保持、映射后的查询更新操作要优于文本、Xparent和DTD等方法。     

多数据库环境下的模式集成及查询分解

在不同数据库表模式间定义了一种结构冲突,并通过元数据的方法,描述了具有结构冲突的表模式间的模式集成。讨论了将集成后的表模式上的查询转换到原表模式上的查询分解方法。     

异构数据源集成中的模式映射技术

模式映射是异构数据源集成中实现查询重形成（Reformulation）的关键技术,本文首先介绍了模式映射的集中式和非集中式集成体系,总结了定义模式映射的3种基本形式：GAV、LAV和GLAV,重点探讨了模式映射中的核心技术：模式匹配和映射生成,最后讨论了模式映射技术新的研究议题。     

不确定模式匹配研究综述

模式匹配是数据集成、语义Web等研究领域的重要研究内容,需要依据一定的启发式信息发现模式元素之间的对应关系。鉴于启发式信息处理方法的不同,对模式匹配方法进行了分类,并从模式匹配结果集结方法的角度,介绍了综合模式匹配方法。不确定性是模式匹配过程固有的特性,介绍了建模模式匹配过程中不确定性的数据模型,在此基础上介绍了处理模式匹配过程中不确定性的模式匹配方法。最后对模式匹配研究进行了展望。     

模式匹配中的依赖冲突

通过分析已有匹配方法的缺陷,提出了一种利用依赖冲突选取匹配关系的新方法.首先为目标模式中每个元素选取候选匹配,然后计算每个全局匹配方案的冲突值,最后选取冲突值最小的匹配方案作为最终结果.实验表明,该方法能够显著提高匹配结果的准确率,并使得后续数据映射结果的优化操作更省时.     

基于模式映射的查询计划生成算法

因特网的迅速发展使得多数据源综合集成日益重要.但是,不同数据源之间数据结构和语义的异构性导致数据集成是相当困难的.本文提出了一种基于模式映射的查询计划生成算法.该算法在正确定义映射规则的前提下,根据不同的查询条件和不同的数据源模式,自动构造查询计划,并保证结果数据满足目标模式结构与引用完整性要求.     

Discovering and using entity mappings in federated databases

In the context of a federated database containing similar information in local component databases, we consider the problem of discovering the different local representations which database designers might use to map the same entity. An extension of the normal SQL system catalog to hold additional domain metadata is discussed. This enables common local mappings to be discovered and allows SQL retrieval queries expressed in terms of the logical federated schema to be transformed to match the appropriate local database schema. The result is a practical means of coping with differing mappings in federated databases without having to resort to special higher order languages or a layer of information mediation middleware. Copyright © 1999 John Wiley & Sons, Ltd.     

基于Shrex的Xquery-SQL查询转换模型的设计与实现

目前还没有一个不依赖于模式映射、且支持复杂嵌套XQuery到SQL的查询转换解决方案.针对现状,设计并实现了一个将XQuery转换为等价SQL的查询转换模型(EXSM).该模型基于Shrex框架,以简洁的方式解决了模式依赖问题,并采用树形中间结构,使之支持复杂的嵌套XQuery.因此,该模型有效地涵盖解决了目前存在的两个问题.     

一种XML Schema模式到关系模式的映射算法

XML文档数据如何存储在主流的关系数据库中,对企业信息集成起着至关重要的作用。针对此问题,提出一种XML Schema模式到关系模式的约束保留映射算法——XSD2RS,该算法基于模式对象组件建模和约束保留机制来完成XML Schema模式到关系模式的映射,进而实现XML文档数据在关系数据库中的存储。     

基于属性实例集合语义相似的模式匹配

近年来,模式匹配作为Web信息集成管理与应用中的重要问题,得到了广泛关注和研究。已有模式匹配方法大多是基于模式信息的,对数据实例信息利用则较少。针对数据集成环境下模式信息不全或存在冲突的模式信息导致模式匹配结果不正确的问题,给出了计算属性间语义相似性的方法以提高模式匹配的性能,分析了模式内语义相近多属性间的语义差别,进一步给出了基于带权二分图最大化算法的模式匹配方法。通过实验,说明基于实例集合语义相似的模式匹配方法能在模式信息不全面或存在冲突的情况下,得到更完整、更准确的模式匹配。     

An XML query rewriting mechanism with multiple ontologies integration based on complex semantic mapping

Semantic integration, which can be divided into three parts including ontology mapping, mapping representation, and reasoning and query rewriting with mappings, plays a key role in information integration systems. This paper develops an XML query rewriting and ontology integration mechanism, which acts as a global-as-view (GAV) approach to represent and query semantic information in mediator based information integration environment. It proposes the patterns and properties of ontology mappings, discusses the procedure and algorithm of ontology integration firstly, and then proposes the ontology based XML query mechanism, especially the XML query rewriting mechanism. Finally, a mediator-based implementation of the mechanism in OBSA system is introduced.     

Schema evolution and integration

Providing support forschema evolution allows existing databases to be adjusted for varying roles over time. This paper reflects on existing evolution support schemes and introduces a more general and functional mechanism to support schema evolution andinstance adaptation for centralized and distributed object-oriented database systems. Our evolution support scheme is distinguished from previous mechanisms in that it is primarily concerned with preserving existing database objects and maintaining compatibility for old applications, while permitting a wider range of evolution operations. It achieves this by supporting schema versioning, allowing multiple representations of instances to persist simultaneously, and providing for programmer specification of how to adapt existing instances. The mechanism is general enough to provide much of the support necessarily forheterogeneous schema integration, as well as incorporating much of the features of object migration and replication.     

SMGM：一种基于模式结构和已有匹配知识的模式匹配模型

模式匹配是确定模式间语义匹配关系的技术，它在许多应用中起着重要的作用，如数据集成中异构模式信息整合、本体知识映射、电子商务中消息映射等。针对已有模式匹配方法的局限性，本着最大限度地减少人工干预使模式匹配自动化的原则，本文提出一种利用模式结构信息和已有匹配知识的模式匹配模型SMGM。它借鉴神经网络元间影响作用过程实现语义匹配推理；通过重用已有匹配知识，补充、精化匹配知识，自动缩减不确定阈值区间；并给出一种自适应式迭代挖掘求精已有匹配知识的自学习型模式匹配模型。实验表明：SMGM模型切实可行。     

Reverse engineering database queries from examples: State-of-the-art,challenges, and research opportunities

With the popularization of data access and usage, an increasing number of users without expert knowledge of databases is required to perform data interactions. Often, these users face the challenges of writing and reformulating database queries, which consume a considerable amount of time and frequently yield unsatisfactory results. To facilitate this human–database interaction, researchers have investigated the Query By Example (QBE) paradigm in which database queries are (semi) automatically discovered from data examples given by users. This paradigm allows non-database experts to formulate queries without relying on complex query languages. In this context, this work aims to present a systematic review of the recent developments, open challenges, and research opportunities of the QBE reported in the literature. This work also describes strategies employed to leverage efficient example acquisition and query reverse engineering. The obtained results show that recent research developments have focused on enhancing the expressiveness of produced queries, minimizing user interaction, and enabling efficient query learning in the context of data retrieval, exploration, integration, and analytics. Our findings indicate that future research should concentrate efforts to provide innovative solutions to the challenges of improving controllability and transparency, considering diverse user preferences in the processes of learning personalized queries, ensuring data quality, and improving the support of additional SQL features and operators.     

关系数据库模式到XML Schema的通用映射模型

基于XML的异构数据库集成技术已经被应用到现有的数据集成平台中,但由于所采用的“模式自动翻译”法的局限性,当前众多的集成平台并不能真正实现异构关系数据库的自由集成。该文在关系模式和XML Schema的形式化定义的基础上,提出描述关系模式到XML Schema的映射关系的通用模型——RtoX,给出模型的合法性验证算法。依据该模型设计了新的关系数据到XML转换的通用算法。     

一种异构数据源模型转换和模式集成框架

异构数据源集成系统的主要任务是屏蔽数据源数据模型的异构性,提供对数据的统一访问。公共数据模型、模型变换和中间数据模型被广泛用来解决该问题。由于数据集成工作的工作量和任务对象日益复杂、规模日趋庞大,仅采用公共数据模型不能满足现有集成要求。异构数据源数据模型内在的关联性虽然使得面向语义集成变得更加复杂,但更利于模型转换方法在数据集成中的应用。模型转换是模式集成的基础,本文给出了异构数据源模型的形式化描述方法和基础模型转换操作形式化框架。该框架能够保证模型、实例和约束三者的相互独立,适用于大多数基础数据模型及其之间的转换和集成应用。通过该框架可简化和规范异构数据源数据模型转换和模式集成过程。     

多数据库系统中查询分解算法的研究

多数据库系统允许用户使用一个集成模式和简单的全局查询语言同时访问多个异构的、自治的数据库系统。全局查询分解处理是多数据库系统中的一个很重要的问题。本文给出了一种多数据库环境中的模式信息管理方法,基于这些模式信息,我们提出一种易于实现的查询分解算法。由于多数据库查询分解处理与模式集成的实现紧密相关,所以本文对多数据库系统的模式集成作了一些描述。     

公共元素模型数据类型的XML Schema描述

AI-ESTATE标准中采用EXPRESS语言对其诊断知识进行描述,但EXPRESS不是程序设计语言,导致采用EXPRESS语言描述的诊断知识难以用程序设计实现,为诊断知识的共享和重用造成了一定困难;XML语言以其良好的灵活性、可读性和可扩展性,为信息交换带来了很大的方便,将EXPRESS语言映射为XML Schema,对诊断知识的共享意义重大.首先,分析了EXPRESS语言和XML Schema的数据类型;然后,分别研究了EXPRESS中简单数据类型、聚合数据类型和构造数据类型到XML数据类型的映射机制;最后,在分析AI-ESTATE标准公共元素模型数据类型的基础上,研究了将公共元素模型的诊断知识用XML Schema标准化描述的过程,实现了诊断知识的可移植和重用.     

Schema mediation for large-scale semantic data sharing

Intuitively, data management and data integration tools should be well suited for exchanging information in a semantically meaningful way. Unfortunately, they suffer from two significant problems: they typically require a common and comprehensive schema design before they can be used to store or share information, and they are difficult to extend because schema evolution is heavyweight and may break backward compatibility. As a result, many large-scale data sharing tasks are more easily facilitated by non-database-oriented tools that have little support for semantics.The goal of the peer data management system (PDMS) is to address this need: we propose the use of a decentralized, easily extensible data management architecture in which any user can contribute new data, schema information, or even mappings between other peers schemas. PDMSs represent a natural step beyond data integration systems, replacing their single logical schema with an interlinked collection of semantic mappings between peers individual schemas.This paper considers the problem of schema mediation in a PDMS. Our first contribution is a flexible language for mediating between peer schemas that extends known data integration formalisms to our more complex architecture. We precisely characterize the complexity of query answering for our language. Next, we describe a reformulation algorithm for our language that generalizes both global-as-view and local-as-view query answering algorithms. Then we describe several methods for optimizing the reformulation algorithm and an initial set of experiments studying its performance. Finally, we define and consider several global problems in managing semantic mappings in a PDMS.Received: 16 December 2002, Accepted: 14 April 2003, Published online: 12 December 2003Edited by: V. Atluri     

Formulating global integrity constraints during derivation of global schema

In a heterogeneous distributed database environment, each component database is characterized by its own logical schema and its own set of integrity constraints. The task of generating a global schema from a constituent local schemata has been addressed by many researchers. The complementary problem of using multiple sets of integrity constraints to create a new set of global integrity constraints is examined in this paper. These global integrity constraints facilitate both query optimization and update validation tasks.