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Unleashing XQuery for Data-Independent Programming

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Abstract

The XQuery language was initially developed as an SQL equivalent for XML data, but its roots in functional programming make it also a perfect choice for processing almost any kind of structured and semi-structured data. Apart from standard XML processing, however, advanced language features make it hard to efficiently implement the complete language for large data volumes. This work proposes a novel compilation strategy that provides both flexibility and efficiency to unleash XQuery’s potential as data programming language. It combines the simplicity and versatility of a storage-independent data abstraction with the scalability advantages of set-oriented processing. Expensive iterative sections in a query are unrolled to a pipeline of relational-style operators, which is open for optimized join processing, index use, and parallelization. The remaining aspects of the language are processed in a standard fashion, yet can be compiled anytime to more efficient native operations of the actual runtime environment. This hybrid compilation mechanism yields an efficient and highly flexible query engine that is able to drive any computation from simple XML transformation to complex data analysis, even on non-XML data. Experiments with our prototype and state-of-the-art competitors in classic XML query processing and business analytics over relational data attest the generality and efficiency of the design.

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Notes

  1. New in XQuery 3.0: http://www.w3.org/TR/xquery-30/

  2. Note, we explicitly distinguish between iterators to iterate over the items of an XQuery sequence, and cursors to iterate over streams of context tuples.

  3. The aggregation specification for non-grouping variables of a GroupBy operator is represented as comma-separated list of XQuery-like expressions in the subscript. The specification $c:($c), for example, says that variable $c is aggregated using the sequence constructor (). The asterisk serves as wildcard for specifying a default aggregation expression.

  4. Source code available at http://brackit.org

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Authors and Affiliations

  1. TU Kaiserslautern, P. O. Box 3049, 67653, Kaiserslautern, Germany

    Sebastian Bächle & Caetano Sauer

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  1. Sebastian Bächle
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  2. Caetano Sauer
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Correspondence to Sebastian Bächle.

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Bächle, S., Sauer, C. Unleashing XQuery for Data-Independent Programming. Datenbank Spektrum 14, 135–150 (2014). https://doi.org/10.1007/s13222-014-0160-3

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