XQuery implementation in a relational database system (original) (raw)

On the path to efficient XML queries

Very Large Data Bases, 2006

XQuery and SQL/XML are powerful new languages for querying XML data. However, they contain a number of stumbling blocks that users need to be aware of to get the expected results and performance. For example, certain language features make it hard if not impossible to exploit XML indexes. The major database vendors provide XQuery and SQL/XML support in their current or upcoming product releases. In this paper, we identify common pitfalls gleaned from the experiences of early adopters of this functionality. We illustrate these pitfalls through concrete examples, explain the unexpected query behavior, and show alternative formulations of the queries that behave and perform as anticipated. As results we provide guidelines for XQuery and SQL/XML users, feedback on the language standards, and food for thought for emerging languages and APIs.

Integrated querying of XML data in RDBMSs

Proceedings of the 2003 ACM symposium on Applied computing - SAC '03, 2003

This paper proposes a way to integrate cleanly relational databases and XML documents. The main idea is to draw a clear line of demarcation between the two concepts by modelling XML documents as a new atomic SQL type. The standardised XML tools like XPath, XQuery, XSLT are then user-defined functions that operate on this type. Welldefined interoperability is guaranteed by, on the one hand, defining a standard way to markup SQL relations as XML documents and, thus, to make them accessible to the XML tools; on the other hand, XPath and XQuery queries run against the XML portion of the database can use the same predefined schema to make their results accessible to the SQL language for further processing. Additionally, a method for set-oriented evaluation of regular path expressions is presented that integrates into our implementation framework.

A general technique for querying XML documents using a relational database system

ACM SIGMOD …, 2001

There has been recent interest in using relational database systems to store and query XML documents. Each of the techniques proposed in this context works by (a) creating tables for the purpose of storing XML documents (also called relational schema generation), (b) storing XML documents by shredding them into rows in the created tables, and (c) converting queries over XML documents into SQL queries over the created tables. Since relational schema generation is a physical database design issue -dependent on factors such as the nature of the data, the query workload and availability of schemas -there have been many techniques proposed for this purpose. Currently, each relational schema generation technique requires its own query processor to efficiently convert queries over XML documents into SQL queries over the created tables. In this paper, we present an efficient technique whereby the same query-processor can be used for all such relational schema generation techniques. This greatly simplifies the task of relational schema generation by eliminating the need to write a special-purpose query processor for each new solution to the problem. In addition, our proposed technique enables users to query seamlessly across relational data and XML documents. This provides users with unified access to both relational and XML data without them having to deal with separate databases. SIGMOD

XML query processing using document type definitions

Journal of Systems and Software, 2002

As eXtensible Markup Language (XML) has become an emerging standard for information exchange on the World Wide Web, it has gained attention in database communities to extract information from XML seen as a database model. Data in XML can be mapped to a semistructured data model based on edge-labeled graph, and queries can be processed against it. Here, we propose new query optimization techniques using document type definitions which have the schema information about XML data. Our techniques reduce the large search space significantly while at the same time requiring less memory compared to the traditional index techniques. Also, as they preserve source database's structure, they can process many kinds of complex queries. We implemented our techniques and provided preliminary performance results.

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

Lecture Notes in Computer Science, 2003

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.

Comparative analysis of five XML query languages

ACM SIGMOD Record, 2000

XML is becoming the most relevant new standard for data representation and exchange on the WWW. Novel languages for extracting and restructuring the XML content have been proposed, some in the tradition of database query languages (i.e. SQL, OQL), others more closely inspired by XML. No standard for XML query language has yet been decided, but the discussion is ongoing within the World Wide Web Consortium and within many academic institutions and Internet-related major companies. We present a comparison of five, representative query languages for XML, highlighting their common features and differences.

Query Formulation and Evaluation for XML Databases

Internet Technologies, Applications and Societal Impact, 2002

The proposed approach to XML query formulation and evaluation developed by means of XML Declamtive Description (XDD) theory formalizes a query as an XDD description comprising one or more XML clauses the syntax of which can be subdivided into the three specifications: pattern of XML elements to be selected, the query's selection criteria and the structure of the resulting elements. It supports formulation of essential functionality requirements for an XML query language such as selection and extraction, combination, transformation, closure and nested queries. Evaluation of a query on a specified XML database is carried out by employment of Equivalent 'I'ransformation paradigm. Moreover, since XDD theory provides a simple mechanism for representation of knowledge and relationships among elements in a The original version of this chapter was revised: The copyright line was incorrect. This has been corrected. The Erratum to this chapter is available at

SQL4X: A Flexible Query Language for XML and Relational Databases

Lecture Notes in Computer Science, 2002

SQL4X, a powerful language for simultaneously querying both relational and XML databases is presented. Using SQL4X, one can create both relations and XML documents as query results. Thus, SQL4X can be thought of as an integration language. In order to allow easy integration of XML documents with varied structures, SQL4X uses flexible semantics when querying XML. SQL4X is also a powerful query language. It can express quantification, negation, aggregation, grouping and path expressions. Datalog4x and Tree-Datalog4x, extensions of Datalog, are defined as elegant abstract models for SQL4X queries. Query containment is characterized for many common classes of SQL4X queries. Specifically, for Datalog4x queries, a complete characterization of containment of conjunctive queries and of unions of queries is presented. Equivalence of Datalog4x queries under bag-set semantics is also characterized. A sufficient condition for containment of Tree-Datalog4x queries is presented. This condition is shown to be complete for a large class of common queries.

Determined: a system with novel techniques for XML query optimization and evaluation

International Journal of Web Information Systems, 2008

PurposeEfficient processing of XML queries is critical for XML data management and related applications. Previously proposed techniques are unsatisfactory. The purpose of this paper is to present Determined – a new prototype system designed for XML query processing and optimization from a system perspective. With Determined, a number of novel techniques for XML query processing are proposed and demonstrated.Design/methodology/approachThe methodology emphasizes on query pattern minimization, logic‐level optimization, and efficient query execution. Accordingly, three lines of investigation have been pursued in the context of Determined: XML tree pattern query (TPQ) minimization; logic‐level XML query optimization utilizing deterministic transformation; and specialized algorithms for fast XML query execution.FindingsDeveloped and demonstrated were: a runtime optimal and powerful algorithm for XML TPQ minimization; a unique logic‐level XML query optimization approach that solely pursues...