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2008
ACM

XPath, transitive closure logic, and nested tree walking automata

10 years 4 months ago
XPath, transitive closure logic, and nested tree walking automata
We consider the navigational core of XPath, extended with two operators: the Kleene star for taking the transitive closure of path expressions, and a subtree relativisation operator, allowing one to restrict attention to a specific subtree while evaluating a subexpression. We show that the expressive power of this XPath dialect equals that of FO(MTC), first order logic extended with monadic transitive closure. We also give a characterization in terms of nested tree-walking automata. Using the latter we then proceed to show that the language is strictly less expressive than MSO. This solves an open question about the relative expressive power of FO(MTC) and MSO on trees. We also investigate the complexity for our XPath dialect. We show that query evaluation be done in polynomial time (combined complexity), but that satisfiability and query containment (as well as emptiness for our automaton model) are 2ExpTime-complete (it is ExpTime-complete for Core XPath). Categories and Subject Des...
Balder ten Cate, Luc Segoufin
Added 08 Dec 2009
Updated 08 Dec 2009
Type Conference
Year 2008
Where PODS
Authors Balder ten Cate, Luc Segoufin
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