An Inflationary Fixed Point Operator in XQuery

ct The backbone of the XML data model, namely ordered, unranked trees, is inherently recursive and it is natural to equip the associated languages with constructs that can query such recursive structures. To get from the recursive axes in XPath, e.g., ancestor and descendant, to XQuery's recursive user-defined functions, language designers took a giant leap, however. User-defined functions in XQuery admit arbitrary types of recursion--a construct that largely evades optimization approaches beyond "procedural" improvements like tail-recursion elimination or unfolding. We introduce a controlled form of recursion in XQuery, an inflationary fixed point operator, 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 [2, 3] and its core transitive...

• Type: Conference
• Year: 2008
• Where: ICDE
• Authors: Loredana Afanasiev, Torsten Grust, Maarten Marx, Jan Rittinger, Jens Teubner
• Keywords: Database, ICDE 2008, Inflationary Fixed Point, Inflationary Fixed Points, Recursive Xquery Expressions