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Definite Clause Grammars For Language Analysis
 

Definite Clause Grammars For Language Analysis

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    Definite Clause Grammars For Language Analysis Definite Clause Grammars For Language Analysis Presentation Transcript

    • Definite Clause Grammars for Language Analysis - A Survey of the Formalism and a Comparison with Augmented Transition Networks
      Fernando C. N. Pereira and David H. D. Warren
      Presentation by Petru REBEJA
    • Mind map
    • An extension of Context Free Grammars (CFG) expressed in definite clauses
      • Each rule is a “syntactic sugar” for a definite clause of logic
      DCGs - Introduction
    • Extended from CFG specifying that:
      Non-terminals can be terms not only atoms
      np(X,S) sentence(S)
      Procedure calls in the RHS of a rule enclosed within ‘{‘ and ‘}’
      noun(N) -> [W], {rootform(W,N), is_noun(N)}.
      DCGs - Formalism
    • sentence( s(NP, VP) ) ->noun_phrase(NP), verb_phrase(VP).
      noun_phrase(np(Det,Noun,Rel) )-> determiner(Det), nounI.Noun),
      rel_clause(Rel).
      noun_phrase(np(Name) ) -> name(Name).
      verb_phrase(vp(TV,NP) ) -> trans_verb(TV), noun_phrase(NP).
      verb_phrase(vp(IV) ) -> intrans_verb(IV).
      rel_clause(rel(that,VP) ) -> [that], verb_phrase(VP).
      rel_clause(rel(nil) ) -> [].
      determiner(det(W) ) -> [W], {is_determiner(W)}.
      noun(n(W) ) -> [W], {is_noun(W)}.
      name(name(W) ) -> [W], {is_name(W)}.
      trans_verb(tv(W) ) -> [W], {is_trans(W)}.
      intrans_verb(iv(W) ) -> [W], {is_intrans(W)}.
      DCG - Example
    • DCG – Example (cont)
    • Finite state machine (Markov model)
      Adds to each arc of the network an arbitrary condition which must be satisfied in order for the arc to be followed
      ATNs - Introduction
    • ATNs - Example
      Definition of the network
      (defnode s
      (cat noun s2
      (setrsubj *)))
      (defnode s2
      (cat verb s3
      (setr v *)))
      (defnode s3
      (up `(sentence
      (subject ,(getrsubj))
      (verb ,(getr v)))))
      • Sample output
      (sentence
      (subject spot)
      (verb runs))
      For more details visit http://www.bookshelf.jp/texi/onlisp/onlisp_24.html
    • Perspicuity – not only a machine for analyzing, but also a description of the language
      Power and generality – more powerful mechanism for building structures
      Conciseness – around half size of ATN
      Advantages of DCG
    • Efficiency – DCG – 8 msec./word; ATN – 34 msec./word
      Flexibility – DCG is in no way tied to a particular parsing/execution mechanism
      Suitability for theoretical work – provide a bridge between the work of theoretical linguists and the work of engineers
      Advantages of DCG (cont)
    • F.Pereira, D. Warren, Definite Clause Grammars for Language Analysis--A Survey of the Formalism and a Comparison with Augmented Transition Networks, 1980
      A. Woods, Augmented Transition Networks for Language Analysis, 1970
      http://www.bookshelf.jp/texi/onlisp/onlisp_24.html
      References