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15
FiniteState Transducers in Language and Speech Processing
 Computational Linguistics
, 1997
"... Finitestate machines have been used in various domains of natural language processing. We consider here the use of a type of transducers that supports very efficient programs: sequential transducers. We recall classical theorems and give new ones characterizing sequential stringtostring transducer ..."
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Cited by 308 (41 self)
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Finitestate machines have been used in various domains of natural language processing. We consider here the use of a type of transducers that supports very efficient programs: sequential transducers. We recall classical theorems and give new ones characterizing sequential stringtostring transducers. Transducers that output weights also play an important role in language and speech processing. We give a specific study of stringtoweight transducers, including algorithms for determinizing and minimizing these transducers very efficiently, and characterizations of the transducers admitting determinization and the corresponding algorithms. Some applications of these algorithms in speech recognition are described and illustrated. 1.
FiniteState Transducers
 in Speech Recognition. Computer Speech and Language
, 1997
"... Abstract. psubsequential transducers are efficient finitestate transducers with p final outputs used in a variety of applications. Not all transducers admit equivalent psubsequential transducers however. We briefly describe an existing generalized determinization algorithm for psubsequential tran ..."
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Cited by 69 (19 self)
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Abstract. psubsequential transducers are efficient finitestate transducers with p final outputs used in a variety of applications. Not all transducers admit equivalent psubsequential transducers however. We briefly describe an existing generalized determinization algorithm for psubsequential transducers and give the first characterization of psubsequentiable transducers, transducers that admit equivalent psubsequential transducers. Our characterization shows the existence of an efficient algorithm for testing psubsequentiability. We have fully implemented the generalized determinization algorithm and the algorithm for testing psubsequentiability. We report experimental results showing that these algorithms are practical in largevocabulary speech recognition applications. The theoretical formulation of our results is the equivalence of the following three properties for finitestate transducers: determinizability in the sense of the generalized algorithm, psubsequentiability, and the twins property. 1
Minimization Algorithms for Sequential Transducers
, 2000
"... We present general algorithms for minimizing sequential finitestate transducers that output strings or numbers. The algorithms are shown to be efficient since in the case of acyclic transducers and for output strings they operate in O(S+E+V+(EV+F)x(Pmax+1)) steps, where S is the sum of ..."
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Cited by 55 (12 self)
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We present general algorithms for minimizing sequential finitestate transducers that output strings or numbers. The algorithms are shown to be efficient since in the case of acyclic transducers and for output strings they operate in O(S+E+V+(EV+F)x(Pmax+1)) steps, where S is the sum of the lengths of all output labels of the resulting transducer, E the set of transitions of the given transducer, V the set of its states, F the set of final states, and Pmax one of the longest of the longest common prefixes of the output paths leaving each state of the transducer. The algorithms apply to a larger class of transducers which includes subsequential transducers.
On the Determinization of Weighted Finite Automata
 SIAM J. Comput
, 1998
"... . We study determinization of weighted finitestate automata (WFAs), which has important applications in automatic speech recognition (ASR). We provide the first polynomialtime algorithm to test for the twins property, which determines if a WFA admits a deterministic equivalent. We also provide ..."
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Cited by 16 (0 self)
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. We study determinization of weighted finitestate automata (WFAs), which has important applications in automatic speech recognition (ASR). We provide the first polynomialtime algorithm to test for the twins property, which determines if a WFA admits a deterministic equivalent. We also provide a rigorous analysis of a determinization algorithm of Mohri, with tight bounds for acyclic WFAs. Given that WFAs can expand exponentially when determinized, we explore why those used in ASR tend to shrink. The folklore explanation is that ASR WFAs have an acyclic, multipartite structure. We show, however, that there exist such WFAs that always incur exponential expansion when determinized. We then introduce a class of WFAs, also with this structure, whose expansion depends on the weights: some weightings cause them to shrink, while others, including random weightings, cause them to expand exponentially. We provide experimental evidence that ASR WFAs exhibit this weight dependence. ...
Determinization of Transducers Over Infinite Words
"... We study the determinization of transducers over infinite words. We consider transducers with all their states final. We give an effective characterization of sequential functions over infinite words. We also describe an algorithm to determinize transducers over infinite words. ..."
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Cited by 7 (2 self)
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We study the determinization of transducers over infinite words. We consider transducers with all their states final. We give an effective characterization of sequential functions over infinite words. We also describe an algorithm to determinize transducers over infinite words.
Deterministic Generalized Automata
 THEORETICAL COMPUTER SCIENCE
, 1995
"... A generalized automaton (GA) is a finite automaton where the single transitions are defined on words rather than on single letters. Generalized automata were considered by K. Hashiguchi who proved that the problem of calculating the size of a minimal GA is decidable. We define the model of determin ..."
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Cited by 6 (0 self)
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A generalized automaton (GA) is a finite automaton where the single transitions are defined on words rather than on single letters. Generalized automata were considered by K. Hashiguchi who proved that the problem of calculating the size of a minimal GA is decidable. We define the model of deterministic generalized automaton (DGA) and study the problem of its minimization. A DGA has the restriction that, for each state, the sets of words corresponding to the transitions of that state are prefix sets. We solve the problem of calculating the number of states of a minimal DGA for a given language, by giving a procedure that effectively constructs a minimal DGA starting from the minimal equivalent (conventional) deterministic automaton.
Finitely Subsequential Transducers
, 2003
"... Finitely subsequential transducers are efficient finitestate transducers with a finite number of final outputs and are used in a variety of applications. Not all transducers admit equivalent finitely subsequential transducers however. We briefly describe an existing generalized determinization al ..."
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Cited by 5 (2 self)
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Finitely subsequential transducers are efficient finitestate transducers with a finite number of final outputs and are used in a variety of applications. Not all transducers admit equivalent finitely subsequential transducers however. We briefly describe an existing generalized determinization algorithm for finitely subsequential transducers and give the first characterization of finitely subsequentiable transducers, transducers that admit equivalent finitely subsequential transducers. Our characterization shows the existence of an efficient algorithm for testing finite subsequentiability. We have fully implemented the generalized determinization algorithm and the algorithm for testing finite subsequentiability. We report
Deciding unambiguity and sequentiality from a finitely ambiguous maxplus automaton
 THEORET. COMPUT. SCI
, 2004
"... Finite automata with weights in the maxplus semiring are considered. The main result is: it is decidable whether a series that is recognized by a finitely ambiguous maxplus automaton is unambiguous, or is sequential. Furthermore, the proof is constructive. A collection of examples is given to illu ..."
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Cited by 5 (2 self)
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Finite automata with weights in the maxplus semiring are considered. The main result is: it is decidable whether a series that is recognized by a finitely ambiguous maxplus automaton is unambiguous, or is sequential. Furthermore, the proof is constructive. A collection of examples is given to illustrate the hierarchy of maxplus series with respect to ambiguity.
Determinization of Transducers Over Finite and Infinite Words
, 2001
"... We study the determinization of transducers over finite and infinite words. The first part of the paper is devoted to finite words. We recall the characterization of subsequential functions due to Choffrut. We describe here a known algorithm to determinize a transducer. In the case of infinite words ..."
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Cited by 3 (0 self)
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We study the determinization of transducers over finite and infinite words. The first part of the paper is devoted to finite words. We recall the characterization of subsequential functions due to Choffrut. We describe here a known algorithm to determinize a transducer. In the case of infinite words, we consider transducers with all their states final. We give an effective characterization of sequential functions over infinite words. We describe an algorithm to determinize transducers over infinite words. This part contains the main novel results of the paper.