Routledge Dictionary of Language and Linguistics
definite clause grammar (abbrev. DCG)
Formalism used in computational linguistics that arose around 1980, as a development of logic programming, used to analyze (and also generate) sentences. Definite clause grammar, abbreviated DCG, is based on the metamorphosis grammar of A.Colmerauer, and is as powerful as the universal Turing machine. For the notation of grammatical regularities definite clause grammar uses a formalism similar to first-order predicate logic: the so-called ‘definite clauses.’ Declaratively interpreted, a set of definite clauses (just like a set of phrase structure rules) produces a description in the given language, while a procedural interpretation can be used to analyze the wellformedness of sentences. In this, the procedure to recognize whether an input sentence is grammatical corresponds to the proof of a theorem in predicate logic, whereby a PROLOG translator (
interpreter) functions as a theorem prover. Definite clause grammars are executable PROLOG programs. The major significance of definite clause grammar is attributed to ‘unification’ ( unification grammar), which makes various things possible, such as checking congruences and constructing representations of syntactic and semantic structure. In this, definite clause grammars are not only recognizing automata, but also so-called transducers. ( also extraposition grammar)
References
Kowalski, R. 1974. Predicate logic as a programming language. Information Processing 74. 569–74.
McCord, M.C.
1982. Using slots and modifiers in logic grammars for natural language. AI 18. 327–67.
Pereira, F.C.N. and D.H.D.Warren. 1980. Definite clause grammars for language analysis. AI 13. 231–78.
Ramsay, A. 1989. Computer and syntactic description of language systems. In S.Bátorí et al. (eds), Computerlinguistik/Computational linguistics. Berlin and New York. 204–18.
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