An Inflationary Fixed Point Operator in XQuery
Loredana Afanasiev, Torsten Grust, Maarten Marx, Jan Rittinger, and Jens Teubner
Proc. of the 24th Int'l Conference on Data Engineering (ICDE), Cancún, Mexico, April 2008.
We introduce a controlled form of recursion in XQuery, an
inflationary fixed point operator, familiar from the context
of relational databases. This operator imposes restrictions on the
expressible types of recursion, but we show that it is sufficiently
versatile to capture a wide range of interesting use cases, including
Regular XPath and its core transitive closure operator.
While the optimization of general user-defined recursive functions in
XQuery appears elusive, we describe how inflationary fixed points can
be efficiently evaluated, provided that the recursive XQuery
expressions are distributive. We test distributivity
syntactically and algebraically, and provide experimental evidence that
XQuery processors can benefit substantially from this mode of
evaluation.
extended versions of this paper have been published