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 L04 Towards Finite State Transducer


                Finite State Transducers (FST)

o  FST is like the finite state automation defined earlier, 
   except each arc is labelled by a pair of symbols:
                    i:o
    where
      i:  symbol in input string
      o:  symbol output by FST when are is taken

+  Ex. arc in finite state transducer corresponding to 'e' in
   'ladake'

             e : ((+pl, -direct), (+sg, +dir))
     q1 +----------------->--------------------+ q2

   Two pairs of symbols:  i : o
    - i is: 'e'
    - o is: '((+pl, -direct), (+sg, +dir))'

   +  Ex.  Morph Analyzer:  Match input with i,
           if successful go ahead & produce o in output

o  Formally: Finite state transducer
   -  Q:         Finite set of states q0, ..., qN
   -  SIGMA_IN:  Finite set of input symbols
   -  SIGMA_OUT: Finite set of pairs output symbols
   -  q0:        Start state (q0 IN Q)
   -  F:         Set of final accepting states (F SUBSET Q)
   -  DELTA (q, i:o) : For every state q, gives a set
      of states that can be reached from q with i in
      SIGMA_IN, and o in SIGMA_OUT.
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