Querying XML Data Research Articles

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.

Storing and querying XML data using denormalized relational databases

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 RDBMS’s. 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.

Xml Data Mediation and Collaboration: A Proposed Comprehensive Architecture and Query Requirements for Using Xml to Mediate Heterogeneous Data Sources and Targets

This paper discusses the potential of using XML technologies as mediators for accessing and processing structured, relational data and semi-structured data over the Internet.Because significant gaps exist in all the reviewed XML data mediation approaches, a more comprehensive framework is presented. Some of the potential benefits of this architecture include: provides a clean abstraction of heterogeneous data for end users, applications, and Internet applications; supports all major data formats; uses one standard query language for all XML data queries; thus, optimizes and simplifying query writing; can be implemented in phases; consistent query language regardless of data source; returns all data results in XML format; provides different views of data according to different application needs; improves Internet spidering; continues to support all necessary DBMS functions; provides a platform for future growth; and encourages coherent and comprehensive data management and data modeling with organizations.

DifX: A Dynamic Index Structure for Querying XML Data Efficiently

DifX: A Dynamic Index Structure for Querying XML Data Efficiently

Containment and equivalence for a fragment of XPath

XPath is a language for navigating an XML document and selecting a set of element nodes. XPath expressions are used to query XML data, describe key constraints, express transformations, and reference elements in remote documents. This article studies the containment and equivalence problems for a fragment of the XPath query language, with applications in all these contexts.In particular, we study a class of XPath queries that contain branching, label wildcards and can express descendant relationships between nodes. Prior work has shown that languages that combine any two of these three features have efficient containment algorithms. However, we show that for the combination of features, containment is coNP-complete. We provide a sound and complete algorithm for containment that runs in exponential time, and study parameterized PTIME special cases. While we identify one parameterized class of queries for which containment can be decided efficiently, we also show that even with some bounded parameters, containment remains coNP-complete. In response to these negative results, we describe a sound algorithm that is efficient for all queries, but may return false negatives in some cases.

X-RESTORE: Middleware for XML’s relational storage and retrieve

We propose a new approach to store and query XML data in an RDBMS basing on the idea of the numbering scheme and inverted list. Our approach allows us to quickly determine the precedence, sibling and ancestor/descendant relationships between any pair of nodes in the hierarchy of XML, and utilize path index to speed up calculating of path expressions. Examples have demonstrated that our approach can effectively and efficiently support both XQuery queries and keyword searches. Our approach is also flexible enough to support XML documents both with Schema and without Schema, and applications both retrieval and update. We also present the architecture of middleware for application accessing XML documents stored in relations, and an algorithm translating a given XML document into relations effectively.

DVQ: Towards Visual Query Processing of XML Database Systems

XML has been recognized as a promising language for data exchange over the Internet. A number of query languages have been proposed for querying XML data. Most of those languages are path-expression based. One difficulty in forming path-expression based queries is that users have to know the structure of XML data against which the queries were issued. In this paper, we describe a DTD-driven visual query interface for XML database systems. With such an interface, a user can easily form path-expression based queries by clicking elements in the DTD tree displayed on the screen and supplying conditions if necessary. The interface and the query generation process are described in detail.

공통 문서 구조 추출을 통한 XML DTD의 관계형 데이터 베이스 스키마 변환 기법

XML은 W3C에 제안된 마크업 언어고 HTML의 단순함과 SGML의 복잡함을 극복하여, 웹 상에서 데이터를 표현하고 교환하기 위한 표준으로 등장하고 있다. XML 문서를 질의 처리하기 위한 방법으로 XML 문서 전용 질의 언어가 개발되고 있지만, 데이터의 양이 증가한다면 결국 막대한 양의 데이터를 처리 할 데이터베이스 시스템을 필요하게 된다. 본 논문에서는 XML DTD를 관계형 데이터베이스 시스템 스키마로 변환하는 기법을 제안한다. 제안된 기법은 XML 데이터의 스키마 역할을 하는 DTD의 트리 구조를 생성하여, XML 데이터들의 공통구조와 비공통구조를 추출한 후 관계형 데이터베이스 스키마를 추출하는 기법이다. 추출된 관계형 데이터베이스 스키마는 기존의 방법들에 비해 생성 테이블 수가 적으며, 널(NULL)값의 출현을 감소시킨다. 또한, 제안기법은 XML 데이터를 보다 적은 테이블로 맵핑(mapping)시킴으로써 데이터 검색 시 참조 테이블 수를 감소시킬 수 있으며 질의 처리 시에도 성능 면에서 우수함을 보인다. XML is emerging as a standard data format to exchange and to present data on the Web. There are increasing needs to efficiently store and to query XML data. In this paper. we propose a new schema transformation algorithm based on a common structure extracting technique from XML documents. The common structure is shared by all XML documents referenced by DTD and the uncommon structure is ununiformly appeared on all XML documents referenced by DTD. Based on the extracted common and uncommon structures, we transform XML DTD into relational database schema. We conduct a performance evaluation based on the number of the generated tables, the size of the record, query processing time and the number of joins on the query. The performance of our algorithm is compared with the existing algorithms, then in most cates, our algorithm is better than the existing ones with respect to the number of the generated tables and appearance of NULL values in the tables.

The XML Query Language Xcerpt: Design Principles, Examples, and Semantics

Most query and transformation languages developed since the mid 90es for XML and semistructured data - e.g. XQuery [1], the precursors of XQuery [2], and XSLT [3] - build upon a path-oriented node selection: A node in a data item is specified in terms of a root-to-node path in the manner of the file selection languages of operating systems. Constructs inspired from the regular expression constructs *, +, ?, and wildcards give rise to a flexible node retrieval from incompletely specified data items. This paper further introduces into Xcerpt, a query and transformation language further developing an alternative approach to querying XML and semistructured data first introduced with the language UnQL [4]. A metaphor for this approach views queries as patterns, answers as data items matching the queries. Formally, an answer to a query is defined as a simulation [5] of an instance of the query in a data item.

CPI: Constraints-Preserving Inlining algorithm for mapping XML DTD to relational schema

As Extensible Markup Language (XML) is emerging as the data format of the Internet era, there are increasing needs to efficiently store and query XML data. One path to this goal is transforming XML data into relational format in order to use relational database technology. Although several transformation algorithms exist, they are incomplete in the sense that they focus only on structural aspects and ignore semantic aspects. In this paper, we present the semantic knowledge that needs to be captured during transformation to ensure a correct relational schema. Further, we show an algorithm that can (1) derive such semantic knowledge from a given XML Document Type Definition (DTD) and (2) preserve the knowledge by representing it as semantic constraints in relational database terms. By combining existing transformation algorithms and our constraints-preserving algorithm, one can transform XML DTD to relational schema where correct semantics and behaviors are guaranteed by the preserved constraints. Experimental results are also presented.

Computing graphical queries over XML data

The rapid evolution of XML from a mere data exchange format to a universal syntax for encoding domain-specific information raises the need for new query languages specifically conceived to address the characteristics of XML. Such languages should be able not only to extract information from XML documents, but also to apply powerful transformation and restructuring operators, based on a well-defined semantics. Moreover, XML queries should be natural to write and understand, as nontechnical persons also are expected to access the large XML information bases supporting their businesses. This article describes XML-GL, a graphical query language for XML data. XML-GL's uniqueness is in the definition of a graph-based syntax to express a wide variety of XML queries, ranging from simple selections to expressive data transformations involving grouping, aggregation, and arithmetic calculations. XML-GL has an operational semantics based on the notion of graph matching, which serves as a guideline both for the implementation of native processors, and for the adoption of XML-GL as a front-end to any of the XML query languages that are presently under discussion as the standard paradigm for querying XML data.

XML data management (panel session)

XML data is likely to be widely used as a data exchange format but users also need to store and query XML data. The purpose of this panel is to explore whether and how to best provide this functionality.

XML-based information mediation with MIX

The MIX mediator system, MIX m , is developed as part of the MIX Project at the San Diego Supercomputer Center, and the University of California, San Diego. 1 MIX m uses XML as the common model for data exchange. Mediator views are expressed in XMAS ( XML Matching And Structuring Language ), a declarative XML query language. To facilitate user-friendly query formulation and for optimization purposes, MIX m employs XML DTDs as a structural description (in effect, a “schema”) of the exchanged data. The novel features of the system include: Data exchange and integration solely relies on XML, i.e., instance and schema information is represented by XML documents and XML DTDs, respectively. XML queries are denoted in XMAS, which builds upon ideas of languages like XML-QL, MSL, Yat, and UnQL. Additionally, XMAS features powerful grouping and order constructs for generating new integrated XML “objects” from existing ones. The graphical user interface BBQ ( Blended Browsing and Querying ) is driven by the mediator view DTD and integrates browsing and querying of XML data. Complex queries can be constructed in an intuitive way, resembling QBE. Due to the nested nature of XML data and DTDs, BBQ provides graphical means to specify the nesting and grouping of query results. Query evaluation can be demand-driven, i.e., by the user's navigation into the mediated view.