Nondeterministic Streaming String Transducers

  • Rajeev Alur
  • Jyotirmoy V. Deshmukh
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6756)


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 functional nssts; 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.


Expressive Power Equivalence Problem Sequential Composition Input String Input Symbol 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2011

Authors and Affiliations

  • Rajeev Alur
    • 1
  • Jyotirmoy V. Deshmukh
    • 1
  1. 1.Dept. of Computer and Information ScienceUniversity of PennsylvaniaUSA

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