Kappa-Join: Efficient Execution of Existential Quantification in XML Query Languages

Brantner, Matthias ; Helmer, Sven ; Kanne, Carl-Christian ; Moerkotte, Guido

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URL: http://ub-madoc.bib.uni-mannheim.de/1227
URN: urn:nbn:de:bsz:180-madoc-12274
Document Type: Working paper
Year of publication: 2006
The title of a journal, publication series: None
Publication language: English
Institution: School of Business Informatics and Mathematics > Sonstige - Fakultät für Wirtschaftsinformatik und Wirtschaftsmathematik
MADOC publication series: Veröffentlichungen der Fakultät für Mathematik und Informatik > Institut für Informatik > Technical Reports
Subject: 004 Computer science, internet
Subject headings (SWD): XML , XQuery , XPath
Keywords (English): Query Optimization
Abstract: XML query languages feature powerful primitives for formulating queries involving comparison expressions which are existentially quantified. If such comparisons involve several scopes, they are correlated, and become difficult to evaluate efficiently. In this paper, we develop a new ternary operator, called Kappa-Join, for efficiently evaluating queries with existential quantification. In XML queries, a correlation predicate can occur conjunctively and disjunctively. Our decorrelation approach not only improves performance in the conjunctive case, but also allows decorrelation of the disjunctive case. The latter is not possible with any known technique. In an experimental evaluation, we compare the query execution times of the Kappa-Join with existing XPath evaluation techniques to demonstrate the effectiveness of our new operator.
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