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Marrying Words and Trees Rajeev Alur
 

Summary: Marrying Words and Trees
Rajeev Alur
University of Pennsylvania
ABSTRACT
Traditionally, data that has both linear and hierarchical
structure, such as annotated linguistic data, is modeled us-
ing ordered trees and queried using tree automata. In this
paper, we argue that nested words and automata over nested
words offer a better way to capture and process the dual
structure. Nested words generalize both words and ordered
trees, and allow both word and tree operations. We study
various classes of automata over nested words, and show
that while they enjoy expressiveness and succinctness bene-
fits over word and tree automata, their analysis complexity
and closure properties are analogous to the corresponding
word and tree special cases. In particular, we show that
finite-state nested word automata can be exponentially more
succinct than tree automata, and pushdown nested word au-
tomata include the two incomparable classes of context-free
word languages and context-free tree languages.

  

Source: Alur, Rajeev - Department of Computer and Information Science, University of Pennsylvania

 

Collections: Computer Technologies and Information Sciences