Finite-state transducer

Summary

A finite-state transducer is a finite automaton with two tapes: it reads an input word and writes an output word. Its transitions are labelled by pairs of input and output pieces. It defines a relation between input words and output words, called a rational relation. Finite-state transducers generalize nondeterministic finite automata, which have only an input tape, and the deterministic Mealy machines. They are used in natural language processing, for example in morphology and speech recognition, and in text rewriting.