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Streaming Tree Transducers Rajeev Alur and Loris D'Antoni

Summary: Streaming Tree Transducers
Rajeev Alur and Loris D'Antoni
University of Pennsylvania
February 21, 2012
Theory of tree transducers provides a foundation for understanding expressiveness and com-
plexity of analysis problems for specification languages for transforming hierarchically structured
data such as XML documents. We introduce streaming tree transducers as an analyzable, exe-
cutable, and expressive model for transforming unranked ordered trees (and hedges) in a single
pass. Given a linear encoding of the input tree, the transducer makes a single left-to-right
pass through the input, and computes the output in linear time using a finite-state control, a
visibly pushdown stack, and a finite number of variables that store output chunks that can be
combined using the operations of string-concatenation and tree-insertion. We prove that the
expressiveness of the model coincides with transductions definable using monadic second-order
logic (MSO). Existing models of tree transducers either cannot implement all MSO-definable
transformations, or require regular look ahead that prohibits single-pass implementation. We
show a variety of analysis problems such as type-checking and checking functional equivalence
are decidable for our model.
1 Introduction
Finite-state machines and logics for specifying tree transformations offer a suitable theoretical foun-


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


Collections: Computer Technologies and Information Sciences