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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.