VIREX and VRXQuery: interactive approach for visual querying of relational databases to produce XML

VIREX provides an interactive approach for querying and integrating relational databases to produce XML documents and the corresponding schemas. VIREX connects to each database specified by the user; analyzes the catalogue to derive an interactive diagram equivalent to the extended entity-relationship diagram; allows the user to display sample records from the tables in the database; allows the user to rename columns and relations by modifying directly the interactive diagram; facilitates the conversion of the relational database into XML; and derives the XML schema. VIREX works even when the catalogue of the relational database is missing; it extracts the required catalogue information by analyzing the database content. Further, VIREX supports VRXQuery, which is a visual naive-users-oriented query language that allows users to specify queries and define views directly on the interactive diagram as a sequence of mouse clicks with minimum keyboard input. The user is expected to interactively decide on certain factors to be considered in producing the XML result. Such factors include: 1) selecting the relations/attributes to be converted into XML; 2) specifying a predicate to be satisfied by the information to be converted into XML; 3) deciding on the order of nesting between the relations to be converted into XML; 4) ordering for the result. VRXQuery supports selection, projection, nesting/join, union, difference, and order-by. As the result of a query, VIREX displays on the screen the XML schema that satisfies the specified characteristics and generates colored (easy to read) XML document(s). Further, VIREX allows the user to display and review the SQL and XQuery equivalent to each query expressed in VRXQuery.     

XQuery视图机制

从XML数据安全性考虑，在已经使用XQuery作为查询语言的前提下，为增强XQuery对XML文档查询能力，创造了类似关系数据库视图的XQuery视图机制，使得不同用户对XML文档具有不同的查看能力，保证查询安全可靠。XQuery视图由查询来定义其内容，分为实视图和虚视图两种。虚视图根据需要计算视图定义的查询，而实视图不管以后是否需要，只要一创建就计算其视图定义，类似关系数据库视图，实视图和虚视图对于数据查询都是必要的。     

Recommending XML physical designs for XML databases

Database systems employ physical structures such as indexes and materialized views to improve query performance, potentially by orders of magnitude. It is therefore important for a database administrator to choose the appropriate configuration of these physical structures for a given database. XML database systems are increasingly being used to manage semi-structured data, and XML support has been added to commercial database systems. In this paper, we address the problem of automatic physical design for XML databases, which is the process of automatically selecting the best set of physical structures for a database and a query workload. We focus on recommending two types of physical structures: XML indexes and relational materialized views of XML data. We present a design advisor for recommending XML indexes, one for recommending materialized views, and an integrated design advisor that recommends both indexes and materialized views. A key characteristic of our advisors is that they are tightly coupled with the query optimizer of the database system, and they rely on the optimizer for enumerating and evaluating physical designs. We have implemented our advisors in a prototype version of IBM DB2 V9, and we experimentally demonstrate the effectiveness of their recommendations using this implementation.     

Query rewritings using views for XPath queries,framework, and methodologies

Query rewriting using views is a technique that allows a query to be answered efficiently by using pre-computed materialized views. It has many applications, such as data caching, query optimization, schema integration, etc. This issue has been studied extensively for relational databases and, as a result, the technology is maturing. For XML data, however, the work is inadequate. Recently, several frameworks have been proposed for query rewriting using views for XPath queries, with the requirement that a rewriting must be complete. In this paper, we study the problem of query rewriting using views for XPath queries without requiring that the rewriting be complete. This will increase its applicability since in many cases, complete rewritings using views do not exist. We give formal definitions for various concepts to formulate the problem, and then propose solutions. Our solutions are built under the framework for query containment. We look into the problem from both theoretic perspectives, and algorithmic approaches. Two methods to generate rewritings using views are proposed, with different characteristics in terms of generalities and efficiencies. The maximality properties of the rewritings generated by these methods are discussed.     

Detecting common subexpressions for multiple query optimization over loosely-coupled heterogeneous data sources

The research presented in this paper supports the identification of common subexpressions as candidates for potential materialized views that form the basis of multiple query optimization in a loosely-coupled distributed system where query expressions access heterogeneous data sources, including relations and data-centric XML. This paper introduces a unifying mixed multigraph formalism to represent SQL, XQuery, and LINQ queries in a common query graph model and a heuristics-based algorithm to detect common subexpressions. The identified common subexpressions represent an opportunity for defining a materialized view to avoid repeating computation. The common subexpressions may access only relations, only XML, or a combination of relations and XML. The mixed multigraph model and the heuristic rules presented in this paper have distinguished advantages over the existing approaches that consider only relational or XML data sources individually. The mixed multigraph model can present SQL, XQuery, and LINQ queries in a single graph model and the heuristic rules are designed to consider the identical and subsumed conditions at the same time. A prototype implementation of the algorithm illustrates the applicability of the approach using various examples from the research literature as well as scenarios over a Criminal Justice enterprise that include common subexpressions across relational and XML data sources.     

关系模式下的XML数据存取技术研究

XML数据具有自描述性和半结构化特征，所以它能够从自身得到能够描述自己的类似于数据库的数据模式，并且对XML数据进行数据库存取。本文对利用关系模式来映射XML模式从而在关系数据库中存取XML数据的技术，进行了研究和初步应用。     

面向XML物化视图远程增量维护的版本管理技术研究

Web应用中以XML为格式的信息查询通常会受到网络传输速度有限等因素的影响.为了减少XML的物化视图与其数据源之间的一致性维护中所需的网络数据传输开销,提出了一种面向远程的XML物化视图增量维护的方法.这种方法根据多用户的查询请求和数据源更新信息,生成视图维护程序代码,以程序代码的网络迁移代替XML视图的重复查询,有效地减少了网络数据传输量.重点介绍了增量维护过程中处于核心的版本管理控制方法,用于维护不同时刻数据更新所对应的视图更新程序代码,有效地适应了多用户各种物化视图的维护需求,并且给出了物化视图增量维护的系统框架.     

Using object deputy model to prepare data for data warehousing

Providing integrated access to multiple, distributed, heterogeneous databases and other information sources has become one of the leading issues in database research and the industry. One of the most effective approaches is to extract and integrate information of interest from each source in advance and store them in a centralized repository (known as a data warehouse). When a query is posed, it is evaluated directly at the warehouse without accessing the original information sources. One of the techniques that this approach uses to improve the efficiency of query processing is materialized view(s). Essentially, materialized views are used for data warehouses, and various methods for relational databases have been developed. In this paper, we first discuss an object deputy approach to realize materialized object views for data warehouses which can also incorporate object-oriented databases. A framework has been developed using Smalltalk to prepare data for data warehousing, in which an object deputy model and database connecting tools have been implemented. The object deputy model can provide an easy-to-use way to resolve inconsistency and conflicts while preparing data for data warehousing, as evidenced by our empirical study.     

Synchronous incremental update of materialized views for PostgreSQL

Materialized views are logically excess stored query results in SQL-oriented databases. This technology can significantly improve the performance of database systems. Although the idea of materialized views came up in the 1980s, only three database management systems, i.e. DB2, Oracle, SQL Server, have been successfully developed completely enough with materialized views so far. The barrier lies in building a module that can incrementally update the materialized views automatically, which corresponds to data changes in the base tables. This paper presents the algorithm to incrementally update the materialized views with inner join, focusing on one with aggregate functions, and building of a program that automatically generates codes inPL/pgSQL for triggers, which can undertake synchronous incremental updates of the materialized views in PostgreSQL.     

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.     

XML queries and algebra in the Enosys integration platform

We describe the Enosys XML integration platform, focusing on the query language, algebra, and architecture of its query processor. The platform enables the development of eBusiness applications in customer relationship management, e-commerce, supply chain management, and decision support. These applications often require that data be integrated dynamically from multiple information sources. The Enosys platform allows one to build (virtual and/or materialized) integrated XML views of multiple sources, using XML queries as view definitions. During run-time, the application issues XML queries against the views. Queries and views are translated into the XCQL algebra and are combined into a single algebra expression/plan. Query plan composition and query plan decomposition challenges are faced in this process. Finally, the query processor lazily evaluates the result, using an appropriate adaptation of relational database iterator models to XML. The paper describes the platform architecture and components, the supported XML query language and the query processor architecture. It focuses on the underlying XML query algebra, which differs from the algebras that have been considered by W3C in that it is particularly tuned to semistructured data and to optimization and efficient evaluation in a system that follows the conventional architecture of database systems.     

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.     

Updating XML views published over relational databases: Towards the existence of a correct update mapping

XML data management using relational database systems has been intensively studied in the last few years. However, in order for such systems to be viable, they must support not only queries, but also updates over virtual XML views that wrap the relational data. While view updating is a long-standing difficult issue in the relational context, the flexible XML data model and nested XML query language both pose additional challenges for view updating.

This paper addresses the question, if for a given update over an XML view, a correct relational update translation exists. First, we propose a clean extended-source theory as criteria for determining whether a given translation mapping is correct. To determine the existence of such a correct mapping, we classify a view update as either un-translatable, conditionally or unconditionally translatable under a given update translation policy. This classification depends on several features of the XML view and the update: (a) granularity of the update at the view side, (b) properties of the view construction, and (c) types of duplication appearing in the view. These features are represented in the Annotated Schema Graph. This is further utilized by our Schema-driven Translatability Reasoning algorithm (STAR) to classify a given update into one of the three above update categories. The correctness of the algorithm is proven using our clean extended-source theory. This technique represents a practical approach that can be applied by any existing view update system in industry and academia for analyzing the translatability of a given update statement before translation of it is attempted. To illustrate the working algorithm, we provide a concrete case study on the translatability of XML view updates.     

Maintaining Views in Object-Relational Databases

View materialization is an important way of improving the performance of query processing. When an update occurs to the source data from which a materialized view is derived, the materialized view has to be updated so that it is consistent with the source data. This update process is called view maintenance. The incremental method of view maintenance, which computes the new view using the old view and the update to the source data, is widely preferred to full view recomputation when the update is small in size. In this paper we investigate how to incrementally maintain views in object-relational (OR) databases. The investigation focuses on maintaining views defined in OR-SQL, a language containing the features of object referencing, inheritance, collection, and aggregate functions including user-defined set aggregate functions. We propose an architecture and algorithms for incremental OR viewmaintenance. We implement all algorithms and analyze the performance of them in comparison with full view recomputation. The analysis shows that the algorithms significantly reduce the cost of updating a vieww hen the size of an update to the source data is relatively small. Received 23 May 2000 / Revised 27 March 2001 / Accepted in revised form 30 April 2001 Correspondence and offprint requests to: Jixue Liu, School of Computer and Information Science, University of South Australia, Mawson Lakes, Adelaide SA5084, Australia. Email: jixue.liu@unisa.edu.auau     

An efficient query evaluation in a mediator based on implementation plan

Recent research which purports to integrate distributed information has been concentrated on developing efficient mediator systems that not only provide a high degree of autonomy for local users, but also support the flexible integration of required functions for global users. However, there has been little attention paid to the implementation of the global views defined in a mediator. It is possible to speed up the execution of a global query if the previous result of a view is materialized in a mediator. Since the integration schema of a mediator can be incrementally modified and its usage can also be continuously varied, view usage should be carefully monitored to determine the optimized set of materialized views. Furthermore, as the number of views increases, the optimization process itself may take too long, so that the optimized set identified by a long optimization process becomes obsolete due to the recent change of view usage. This paper proposes the adaptive selection of a practical implementation method for each global view, such that available storage in a mediator can be highly utilized at any time. In order to differentiate the recent usage of a view from the past, the accumulated usage frequency of a view decays as time goes by. As a result, it is possible to change the implementation of each view adaptively with respect to the recent variation of view usage.     

AnyQuery:网格环境下基于服务的分布式查询处理系统

AnyQuery是一种适用于网格环境、基于服务的分布式查询处理系统，使用统一的数据格式（可扩展标记语言）来表示和传输数据，所有组成模块以网格服务的形式实现，网格服务之间通过标准的接口进行通信．这种接口和实现分离技术屏蔽了不同数据库及其运行节点的差异，为用户提供一致的虚拟关系数据视图和分布式数据查询支持．在分析和研究已有的并行数据库和分布式数据库查询技术的基础上，AnyQuery提出和实现了一种适用于动态网格环境的分布式查询计划生成和执行算法，该算法能够根据网格环境中各节点及其连接网络的实际情况确定查询计划，支持跨数据库的连接查询．基于Globus 3．0开发了AnyQuery的原型系统，性能测试表明该系统具有较好的可扩展性，尤其适合计算密集型的复杂查询．     

基于X-RESTORE查询XML视图

基于转换 XML文档到关系数据库中进行存储与查询的策略 ,研究了 XML视图查询的有效计算问题 .提出了XML 视图查询的合成重写技术 ,它能够消除视图查询中所有在视图结构上的路径导航操作 ,并将视图查询中所有在原文档结构上的路径导航操作以及所有谓词操作下推到视图定义中去 ,与视图定义中的路径导航操作相结合 ,形成统一的在原文档结构上的路径导航操作 .视图合成重写不仅避免了对视图中不出现在最后结果中的中间 XML 片段的构造 ,而且允许将查询中的所有内存密集型或数据密集型操作尽量下推到关系引擎中去执行 ,从而提高 XQuery查询的执行性能     

A relational–XML data warehouse for data aggregation with SQL and XQuery

Integrating information from multiple data sources is becoming increasingly important for enterprises that partner with other companies for e‐commerce. However, companies have their internal business applications deployed on diverse platforms and no standard solution for integrating information from these sources exists. To support business intelligence query activities, it is useful to build a data warehouse on top of middleware that aggregates the data obtained from various heterogeneous database systems. Online analytical processing (OLAP) can then be used to provide fast access to materialized views from the data warehouse. Since extensible markup language (XML) documents are a common data representation standard on the Internet and relational tables are commonly used for production data, OLAP must handle both relational and XML data. SQL and XQuery can be used to process the materialized relational and XML data cubes created from the aggregated data. This paper shows how to handle the two kinds of data cubes from a relational–XML data warehouse using extract, transformation and loading. Copyright © 2008 John Wiley & Sons, Ltd.     

Optimizing updates of recursive XML views of relations

XML publishing has been an emerging technique for transforming (portions of) a relational database into an XML document, for example, to facilitate interoperability between heterogeneous applications. Such applications may update the XML document and the source relational database must be updated accordingly. In this paper, we consider such XML documents as (possibly) recursively defined XML views of relations. We propose new optimization techniques to efficiently support XML view updates specified via an XPATH expression with recursion and complex filters. The main novelties of our techniques are: (1) we propose a space-efficient relational encoding of recursive XML views; and (2) we push the bulk of update processing inside a relational database. Specifically, a compressed representation of the XML views is stored as extended shared-inlining relations. A space-efficient and updatable 2-hop index is used to optimize XPATH evaluation on XML views. Updates of the XML views are evaluated on these relations and index. View update translation is handled by a heuristic procedure inside a relational database, as opposed to previous middleware approaches. We present an experimental study to demonstrate the effectiveness of our proposed techniques.     

Integrating XML and Relational Database Systems

Relational databases get more and more employed in order to store the content of a web site. At the same time, XML is fast emerging as the dominant standard at the hypertext level of web site management describing pages and links between them. Thus, the integration of XML with relational database systems to enable the storage, retrieval, and update of XML documents is of major importance. Data model heterogeneity and schema heterogeneity, however, make this a challenging task. In this respect, the contribution of this paper is threefold. First, a comparison of concepts available in XML schema specification languages and relational database systems is provided. Second, basic kinds of mappings between XML concepts and relational concepts are presented and reasonable mappings in terms of mapping patterns are determined. Third, design alternatives for integrating XML and relational database systems are examined and X-Ray, a generic approach for integrating XML with relational database systems is proposed. Finally, an in-depth evaluation of related approaches illustrates the current state of the art with respect to the design goals of X-Ray.