Rainbow

2010

Abstract. Efficient processing of XPath expressions is an integral part of XML data query processing. Exploiting materialized views in query processing can significantly enhance query processing performance. We propose a novel view definition that allows for intermediate (structural) join results to be stored and reused in XML query evaluation. Unlike current XML view proposals, our views do not require navigation in the original document or path-based pattern matching.

Label Streams, Semantics Utilization and Data Query Technologies

In the last few years, XML became a de-facto standard for the exchange of structured and semi-structured data. The database research community took this development into account by proposing native XML database management systems for efficient and transactional management of XML documents. One of the most important factors for success of such systems is a powerful query optimizer. Many researchers proposed sophisticated Structural Join and Holistic Twig Join algorithms as well as several index structures supporting the evaluation of twig query patterns. Even though almost all XML query evaluation approaches proposed so far use some of these methods, we believe that they provide no sufficient input for real-world cost-based query optimization scenarios, because they only cover a small part of the overall query evaluation process. To provide adequate input for a cost-based XML query optimizer, we propose the XML Query Graph Model as a new internal representation enabling a smooth transition between XQuery language level and physical algebra operators. Furthermore, we introduce a set of rewrite rules for improving the execution of twig queries, e. g., by fusing two adjacent binary join operators to a complex n-way join operator. By presenting further rewrite rules, we make the most of existing joins and indexes-even before query transformation. Using these concepts, we are ready to sketch its integration into our upcoming costbased XML query optimizer. * This work has been supported by the Rheinland-Pfalz cluster of excellence "Dependable adaptive systems and mathematical modelling" (see http://www.dasmod.de).

Proceedings of the …, 2007

The performance of XML database queries can be greatly enhanced by rewriting them using materialized views. We study the problem of rewriting a query using materialized views, where both the query and the views are described by a tree pattern language, ...

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.

2007

Lecture Notes in Computer Science, 2006

As XML applications become more complex, there is a growing interest in extending XQuery with side-effect operations, notably XML updates. Unfortunately, the presence of side-effects is at odds with XQuery's declarative semantics which favors optimization. In this paper, we propose a semantic framework that enables extending XQuery with side-effect operations, while preserving the benefits of XQuery's declarative semantics when possible. We use that framework to define "XQuery!", an extension of XQuery 1.0 that supports first-class XML updates and user-level control over update application. We show that those extensions can be easily implemented within an existing XQuery processor and how to recover basic database optimizations for such a language.

Proceedings 2004 VLDB Conference, 2004

XML languages, such as XQuery, XSLT and SQL/XML, employ XPath as the search and extraction language. XPath expressions often define complicated navigation, resulting in expensive query processing, especially when executed over large collections of documents. In this paper, we propose a framework for exploiting materialized XPath views to expedite processing of XML queries. We explore a class of materialized XPath views, which may contain XML fragments, typed data values, full paths, node references or any combination thereof. We develop an XPath matching algorithm to determine when such views can be used to answer a user query containing XPath expressions. We use the match information to identify the portion of an XPath expression in the user query which is not covered by the XPath view. Finally, we construct, possibly multiple, compensation expressions which need to be applied to the view to produce the query result. Experimental evaluation, using our prototype implementation, shows that the matching algorithm is very efficient and usually accounts for a small fraction of the total query compilation time.

2001

Abstract In this paper we address the problem of adding XML interface to existing relational database solutions by providing mechanisms for storing, retrieving and querying information which resides in relational database by XML means. These mechanisms should be transparent enough to allow a database to act as a simple set of XML documents with the advantage of much more efficient querying.

2010

The increasing volume of data stored as XML documents makes fragmentation techniques an alternative to the performance issues in query processing. Fragmented databases are feasible only if there is a transparent way to query the distributed database. Fragments allow for intra-query parallel processing and data reduction. This paper presents our methodology for XQuery query processing over distributed XML databases. The methodology comprises the steps of query decomposition, data localization, and global optimization. This methodology can be used in an XML database or in a system that publishes homogeneous views of semi-autonomous databases. An implementation has been done and experimental results can achieve performance improvements of up to 95% when compared to the centralized environment.

SOFSEM 2006: Theory and Practice of Computer Science, 2006

Sedna is an XML database system being developed by the MODIS team at the Institute for System Programming of the Russian Academy of Sciences. Sedna implements XQuery and its data model exploiting techniques developed specially for this language. This paper describes the main choices made in the design of Sedna, sketches its most advanced techniques, and presents its overall architecture. In this paper we primarily focus on physical aspects of the Sedna implementation. 1 We have also contributed to this work by developing a set of logical optimization techniques for XQuery [5, 6, 7].