Recursion in XQuery: Put Your Distributivity Safety Belt On
Authors
- Loredana Afanasiev (University of Amsterdam, The Netherlands)
- Torsten Grust (Universität Tübingen, Germany)
- Maarten Marx (ISLA, University of Amsterdam, The Netherlands)
- Jan Rittinger (Universität Tübingen, Germany)
- Jens Teubner (ETH Zurich, Switzerland)
Abstract
We introduce a controlled form of recursion in XQuery, inflationary fixed points, familiar in the context of relational databases. This imposes restrictions on the expressible types of recursion, but we show that inflationary fixed points nevertheless are sufficiently versatile to capture a wide range of interesting use cases, including the semantics of Regular XPath and its core transitive closure construct.
While the optimization of general user-defined recursive functions in XQuery appears elusive, we will describe how inflationary fixed points can be efficiently evaluated, provided that the recursive XQuery expressions exhibit a distributivity property. We show how distributivity can be assessed both, syntactically and algebraically, and provide experimental evidence that XQuery processors can substantially benefit during inflationary fixed point evaluation.
Session
EDBT Research Session 10: XML, XPath, XQuery (Wednesday, March 25, 11:00—12:30)