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UnQL: a query language and algebra for semistructured data based on structural recursion

Authors:

Mary Fernandez,

Dan SuciuAuthors Info & Claims

The VLDB Journal — The International Journal on Very Large Data Bases, Volume 9, Issue 1

Pages 76 - 110

https://doi.org/10.1007/s007780050084

Published: 01 March 2000 Publication History

Abstract

This paper presents structural recursion as the basis of the syntax and semantics of query languages for semistructured data and XML. We describe a simple and powerful query language based on pattern matching and show that it can be expressed using structural recursion, which is introduced as a top-down, recursive function, similar to the way XSL is defined on XML trees. On cyclic data, structural recursion can be defined in two equivalent ways: as a recursive function which evaluates the data top-down and remembers all its calls to avoid infinite loops, or as a bulk evaluation which processes the entire data in parallel using only traditional relational algebra operators. The latter makes it possible for optimization techniques in relational queries to be applied to structural recursion. We show that the composition of two structural recursion queries can be expressed as a single such query, and this is used as the basis of an optimization method for mediator systems. Several other formal properties are established: structural recursion can be expressed in first-order logic extended with transitive closure; its data complexity is PTIME; and over relational data it is a conservative extension of the relational calculus. The underlying data model is based on value equality, formally defined with bisimulation. Structural recursion is shown to be invariant with respect to value equality.

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Index Terms

UnQL: a query language and algebra for semistructured data based on structural recursion
1. Information systems
  1. Data management systems
    1. Query languages

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cover image The VLDB Journal — The International Journal on Very Large Data Bases

The VLDB Journal — The International Journal on Very Large Data Bases Volume 9, Issue 1

March 2000

110 pages

ISSN:1066-8888

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Springer-Verlag

Berlin, Heidelberg

Publication History

Published: 01 March 2000

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https://dl.acm.org/doi/10.1145/3640310.3674083
Guo QZhang CZhang SLu J(2024)Multi-model query languages: taming the variety of big dataDistributed and Parallel Databases10.1007/s10619-023-07433-142:1(31-71)Online publication date: 1-Mar-2024
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Boneva IGroz BHidders JMurlak FStaworko SGeerts FNgo HSintos S(2023)Static Analysis of Graph Database TransformationsProceedings of the 42nd ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems10.1145/3584372.3588654(251-261)Online publication date: 18-Jun-2023
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