Probabilistic grammars and their applications

Formal grammars are widely used in speech recognition, language translation, and language understanding systems. Grammars rich enough to accommodate natural language generate multiple interpretations of typical sentences. These ambiguities are a fundamental challenge to practical application. Grammars can be equipped with probability distributions, and the various parameters of these distributions can be estimated from data (e.g., acoustic representations of spoken words or a corpus of hand-parsed sentences). The resulting probabilistic grammars help to interpret spoken or written language unambiguously. This article reviews the main classes of probabilistic grammars and points to some active areas of research.