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Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
Definite Clause Grammars For Language Analysis
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Definite Clause Grammars For Language Analysis

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  • 1. 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
  • 2. Mind map
  • 3. 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
  • 4. 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
  • 5. 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
  • 6. DCG – Example (cont)
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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)
  • 11. 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

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