共查询到20条相似文献,搜索用时 0 毫秒
1.
XML database systems emerge as a result of the acceptance of the XML data model. Recent works have followed the promising approach of building XML database management systems on underlying RDBMSs. Achieving query processing performance reduces to two questions: (i) How should the XML data be decomposed into data that are stored in the RDBMS? (ii) How should the XML query be translated into an efficient plan that sends one or more SQL queries to the underlying RDBMS and combines the data into the XML result? We provide a formal framework for XML Schema-driven decompositions, which encompasses the decompositions proposed in prior work and extends them with decompositions that employ denormalized tables and binary-coded XML fragments. We provide corresponding query processing algorithms that translate the XML query conditions into conditions on the relational tables and assemble the decomposed data into the XML query result. Our key performance focus is the response time for delivering the first results of a query. The most effective of the described decompositions have been implemented in XCacheDB, an XML DBMS built on top of a commercial RDBMS, which serves as our experimental basis. We present experiments and analysis that point to a class of decompositions, called inlined decompositions, that improve query performance for full results and first results, without significant increase in the size of the database.Received: 21 December 2001, Accepted: 1 July 2003, Published online: 23 June 2004Edited by: A. HalevyAndrey Balmin: Andrey Balmin has been supported by NSF IRI-9734548.Yannis Papakonstantinou: The authors built the XCacheDB system while on leave at Enosys Software, Inc., during 2000. 相似文献
4.
XML已经成为数据表示和交换的数据格式标准。随着大量XML文档的出现,应用数据库技术实现对XML数据的管理引起了越来越多研究者的兴趣。作为研究XML数据库技术的一个开始点,通过与关系数据库比较,可以深刻理解XML数据库与关系数据库的异同,进而为解决XML数据库所面临的问题,如为数据冗余控制、并发访问控制等提供必要的基础。两种数据库的比较是从数据模型、查询路径、完整性约束和规范化5个方面进行的,由于数据模型是数据库的基石,二者的数据模型从构造机制、名字的惟一性、空值、实体标识、实体问关系、文档顺序、数据结构的规则性、递归、数据自描述性等9个方面进行了详细讨论。 相似文献
5.
Modeling spatiotemporal data, in particular fuzzy and complex spatial objects representing geographic entities and relations, is a topic of great importance in geographic information systems, computer vision, environmental data management systems, etc. Because of complex requirements, it is challenging to represent spatiotemporal data and its features in databases and to effectively query them. This article presents a new approach to model and query the spatiotemporal data of fuzzy spatial and complex objects and/or spatial relations. In our case study, we use a meteorological database application in an intelligent database architecture, which combines an object-oriented database with a knowledgebase for modeling and querying spatiotemporal objects. 相似文献
6.
One of the main objectives of third generation databases is to design database management systems which provide users with more and more functionalities. In such a wide context, various proposals have been made in order to introduce some kind of explicit or implicit flexibility into user queries. In this paper, we propose a classification of the various approaches dealing with imprecise queries. Moreover, we show that the approach based on fuzzy sets is powerful enough to answer a wide range of imprecise queries in an appropriate way and to support the expression of the capabilities available in the other classes of solutions. An outline of an SQL-like language allowing for a variety of imprecise queries is also presented. 相似文献
7.
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. 相似文献
8.
The existence of unacceptable components, which consist of unacceptable tuples and elements in attribute values, is shown in fuzzy relational databases. The unacceptable components are created by update operations, insertion, deletion, and modification. An unacceptable tuple in a relation is a tuple such that the degree of its not belonging to that relation is greater than that of its belonging to. The unacceptable tuple can be easily eliminated from relations. There are three kinds of unacceptable elements. One case of unacceptable elements is a redundant element created by insertion and modification. Another is an element created by a possible tuple value not at all or partially satisfying integrity constraints in insertion and modification. The other is an element created by a possible tuple value completely or partially satisfying update conditions in deletion. The unacceptable elements can be eliminated from relations without loss of information. As a result, we can obtain fuzzy relational databases without unacceptable components by a reasonable way. © 1996 John Wiley & Sons, Inc. 相似文献
9.
This paper deals with the connections existing between fuzzy set theory and fuzzy relational databases. Our new result dealing with fuzzy relations is how to calculate the greatest lower bound ( glb) of two similarity relations. Our main contributions in fuzzy relational databases are establishing from fuzzy set theory what a fuzzy relational database should be (the result is both surprising and elegant), and making fuzzy relational databases even more robust.Our work in fuzzy relations and in fuzzy databases had led us into other interesting problems—two of which we mention in this paper. The first is primarily mathematical, and the second provides yet another connection between fuzzy set theory and artificial intelligence. In understanding similarity relations in terms of other fuzzy relations and in making fuzzy databases more robust, we work with closure and interior operators; we present some important properties of these operators. In establishing the connection between fuzzy set theory and artificial intelligence, we show that an abstraction on a set is in fact a partition on the set; that is, an abstraction defines an equivalence relation on the underlying set. 相似文献
10.
对于基于DTD在关系数据库中存储XML文档,此处利用结点模型映射方法,实现用关系模式来表示目标XML文档的逻辑结构(即 XML模式或DTD).还介绍了如何在已建立好的关系模式中添加约束用来保持原有XML文档中隐含的约束信息,此外XML文档的元素之间通常是相互递归的,这里也对XML文档中在出现递归的情况时,如何来存储递归的XML文档进行说明.最后通过举例,证明此种方法是合理有效的. 相似文献
11.
Data streams are long, relatively unstructured sequences of characters that contain information such as electronic mail or a tape backup of various documents and reports created in an office. A conceptual framework is presented, using relational algebra and relational databases, within which data streams may be queried. As information is extracted from the data streams, it is put into a relational database that may be queried in the usual manner. The database schema evolves as the user's knowledge of the content of the data stream changes. Operators are defined in terms of relational algebra that can be used to extract data from a specially defined relation that contains all or part of the data stream. This approach to querying data streams permits the integration of unstructured data with structured data. The operators defined extend the functionality of relational algebra in much the same way that the join does relative to the basic operators select, project, union, difference, and Cartesian product 相似文献
12.
An important issue in extending database management systems functionalities is to allow the expression of imprecise queries to enable these systems to satisfy the user needs more closely. This paper deals with imprecise querying of regular relational databases. The basic idea is to extend an existing query language, namely SQL. In this context, two important points must be considered: one concerns the integration in the extended language of many propositions that have been made elsewhere, in particular those concerning fuzzy aggregation operators; and the second point is to know whether the equivalences which are valid in SQL still hold in the extended language. Both these topics are investigated in this paper 相似文献
13.
Data mining is an important real-life application for businesses. It is critical to find efficient ways of mining large data sets. In order to benefit from the experience with relational databases, a set-oriented approach to mining data is needed. In such an approach, the data mining operations are expressed in terms of relational or set-oriented operations. Query optimization technology can then be used for efficient processing. In this paper, we describe set-oriented algorithms for mining association rules. Such algorithms imply performing multiple joins and thus may appear to be inherently less efficient than special-purpose algorithms. We develop new algorithms that can be expressed as SQL queries, and discuss optimization of these algorithms. After analytical evaluation, an algorithm named SETM emerges as the algorithm of choice. Algorithm SETM uses only simple database primitives, viz., sorting and merge-scan join. Algorithm SETM is simple, fast, and stable over the range of parameter values. It is easily parallelized and we suggest several additional optimizations. The set-oriented nature of Algorithm SETM makes it possible to develop extensions easily and its performance makes it feasible to build interactive data mining tools for large databases. 相似文献
14.
A new definition of Fuzzy Relational Database is given by using logical concepts. With this definition it is possible to consider several kinds of fuzziness for the database attributes. A Domain Calculus-based query language is also established for the model. It allows us to formulate several types of queries with different lack of precision levels. © 1994 John Wiley & Sons, Inc. 相似文献
15.
XML instances are not necessarily self-contained but may have connections to remote XML data residing on other servers. In this paper, we show that—in spite of its minor support and use in the XML world—the XLink language provides a powerful mechanism for expressing such links both from the modeling point of view and for actually querying interlinked XML data: in our dbxlink approach, the links are not seen as explicit links (where the users must be aware of the links and traverse them explicitly in their queries), but define views that combine into a logical, transparent XML model which serves as an external schema and can be queried by XPath/XQuery. We motivate the underlying modeling and give a concise and declarative specification as an XML-to-XML mapping. We also describe the implementation of the model as an extension of the eXist [eXist: an Open Source Native XML Database, http://exist-db.org/] XML database system. The approach can be applied both for distribution of data and for integration of data from autonomous sources. 相似文献
16.
Since semi-structured documents (e.g., XML) could benefit greatly from database support and more specifically from object-oriented (OO) database management systems, we study the methodology of reengineering XML to object-oriented databases when database migration occurs in this paper. In particular, considering the need of processing the imprecise and uncertain information existing in practical applications, we investigate the problem of migrating fuzzy XML to fuzzy object-oriented databases. To find the object-oriented schema that best describes the existing fuzzy XML schema (DTD), we devise a comprehensive approach centering on a set of mapping rules. Such reengineering practices could not only provide a significant consolidation of the interoperability between fuzzy OO and fuzzy XML modeling techniques, but also develop the practical design methodology for fuzzy OO databases. 相似文献
17.
The need to incorporate and treat information given in fuzzy terms in Relational Databases has concentrated a great effort in the last years. This article focuses on the treatment of functional dependencies (f.d.) between attributes of a relation scheme. We review other approaches to this problem and present some of its missfunctions concerning intuitive properties a fuzzy extension of f.d. should verify. Then we introduce a fuzzy extension of this concept to overcome the previous anomalous behaviors and study its properties. of primary interest is the completeness of our fuzzy version of Armstrong axioms in order to derive all the fuzzy functional dependencies logically implied by a set of f.f.d. just using these axioms. © 1994 John Wiley & Sons, Inc. 相似文献
18.
XML has become the standard for publishing and exchanging data on the Web. Since most of the business data nowadays are stored in structured databases including relational and object-oriented databases (OODB), it is of significance to automate the transformation process and generate the XML data containing information from existing databases. At the same time, information imprecision and uncertainty exist in many practical applications, and for this reason, fuzzy data modeling has been extensively investigated in various data models. As such, there is an increasing need to effectively publish fuzzy structured data as fuzzy XML documents for Web-based applications. In this paper, we take a significant step in a fundamental consolidation of fuzzy XML. In particular, we are interested in finding an XML schema that best describes the existing fuzzy object-oriented schema. To accomplish this, we first offer mapping formalisms to capture the semantics of fuzzy XML Schema and fuzzy object-oriented schema. To allow for better and platform independent sharing of data stored in an object-oriented format, we investigate the formal transformation from fuzzy OODB to fuzzy XML and develop a set of rules to assist in the transformation process. 相似文献
19.
Searching XML data with a structured XML query can improve the precision of results compared with a keyword search. However, the structural heterogeneity of the large number of XML data sources makes it difficult to answer the structured query exactly. As such, query relaxation is necessary. Previous work on XML query relaxation poses the problem of unnecessary computation of a big number of unqualified relaxed queries. To address this issue, we propose an adaptive relaxation approach which relaxes a query against different data sources differently based on their conformed schemas. In this paper, we present a set of techniques that supports this approach, which includes schema-aware relaxation rules for relaxing a query adaptively, a weighted model for ranking relaxed queries, and algorithms for adaptive relaxation of a query and top- k query processing. We discuss results from a comprehensive set of experiments that show the effectiveness and the efficiency of our approach. 相似文献
20.
近来XML已成为科学与业务应用中数据表示的标准以及Web上应用间数据交换的标准。然而,必须看到即使在全新的基于Web的应用中,大量的数据已经并将继续在关系数据库中存储和管理,这就有必要将关系数据出版为XML文档。综述了两类典型的XML出版方法:支持视图的方法和不支持视图的方法,并从多个角度对这些方法进行了分析。 相似文献
|