Nondeterministic Streaming String Transducers
We introduce nondeterministic streaming string transducers (nssts) – a new computational model that can implement MSO-definable relations between strings. An nsst makes a single left-to-right pass on the input string and uses a finite set of string variables to compute the output. In each step, it reads one input symbol, and updates its string variables in parallel with a copyless assignment. We show that nsst are closed under sequential composition and that their expressive power coincides with that of nondeterministic MSO-definable transductions. Further, we identify the class of functionalnssts; such an nsst allows nondeterministic transitions, but for every successful run on a given input generates the same output string. We show that deciding functionality of an arbitrary nsst is decidable with pspace complexity, while the equivalence problem for functional nssts is pspace-complete. We also show that checking if the set of outputs of an nsst is contained within the set of outputs of a finite number of dssts is decidable in pspace.
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- 1.Alur, R., Černý, P.: Expressiveness of streaming string transducers. In: Proc. of Foundations of Software Technology and Theoretical Computer Science, pp. 1–12 (2010)Google Scholar
- 2.Alur, R., Černý, P.: Streaming transducers for algorithmic verification of single-pass list-processing programs. In: Proc. of Principles of Programming Languages, pp. 599–610 (2011)Google Scholar
- 11.Sakarovitch, J., de Souza, R.: On the decidability of bounded valuedness for transducers. In: Proc. of Mathematical Foundations of Computer Science, pp. 588–600 (2008)Google Scholar
- 12.Schützenberger, M.P.: Sur les relations rationelles entre monoïdes libres. Theor. Comput. Sci., 243–259 (1976)Google Scholar