Natural Language Processing

11 Feb 2004*

CS 3243 - Optional Lecture - NLP

21

Definite Clause Grammar (DCG)

lEach grammar rule is a definite clause in logic:

l

lS ® NP VP

lNP(s1) Ù VP(s2) Þ S(s1 + s2)

lNP(case) ® Pronoun(case)

lPronoun(case, s1) Þ NP(case, s1)

l

lDCG enables parsing as logical inference:

lTop-down parsing is backward chaining

lBottom-up parsing is forward chaining