This document compares definite clause grammars (DCGs) and augmented transition networks (ATNs) for language analysis. DCGs extend context-free grammars by allowing non-terminals to be terms rather than just atoms, and allow procedure calls in rule right-hand sides. DCGs are more powerful, concise, efficient and flexible than ATNs, while also being well-suited for theoretical linguistic work.

1. Definite Clause Grammars for Language Analysis - A Survey of the Formalism and a Comparison with Augmented Transition NetworksFernando C. N. Pereira and David H. D. WarrenPresentation by Petru REBEJA

2. Mind map

3. An extension of Context Free Grammars (CFG) expressed in definite clausesEach rule is a “syntactic sugar” for a definite clause of logicDCGs - Introduction

4. Extended from CFG specifying that:Non-terminals can be terms not only atomsnp(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 followedATNs - Introduction

8. ATNs - ExampleDefinition 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 languagePower and generality – more powerful mechanism for building structuresConciseness – around half size of ATNAdvantages of DCG

10. Efficiency – DCG – 8 msec./word; ATN – 34 msec./wordFlexibility – DCG is in no way tied to a particular parsing/execution mechanismSuitability for theoretical work – provide a bridge between the work of theoretical linguists and the work of engineersAdvantages 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, 1980A. Woods, Augmented Transition Networks for Language Analysis, 1970http://www.bookshelf.jp/texi/onlisp/onlisp_24.htmlReferences