Probabilistic Context-Free Grammar

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A Probabilistic Context-Free Grammar is a context free phrase-structure grammar where each production rule is a probabilistic production rule.



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  • (Kakkonen, 2007) ⇒ Tuomo Kakkonen. (2007). “Framework and Resources for Natural Language Evaluation." Academic Dissertation. University of Joensuu.
    • In probabilistic grammar formalisms a probability is associated with each rule. For example, probabilistic context-free grammars (PCFGs) can be characterized as CFPSGs that assign to each production the probability of its use. A PCFG (Booth & Thompson 1973) is a 4-tuple G = (N, Σ, P, S) like a CFPSG (Definition 3-9), except that each rule in P is associated with a probability in which [math]\displaystyle{ α }[/math] will be expanded to β.
    • Definition 3-10. Productions in probabilistic context-free phrase structure grammar.
      • 1. P = {a ®b a Î N,b Î(ΣÈN)*}.
      • 2. There is a probability function p: P→[0,1] such that for each a ÎN,Σ p(a ®b a )= 1.

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