Catalogue of Artificial Intelligence Techniques
Head-driven Phrase Structure Grammar
Keywords: Transformational Grammar
Categories: Natural Language
Author(s): Nicolas Nicolov
Head-Driven Phrase Structure Grammar (HPSG) is an integrated theory of natural language syntax and semantics. HPSG is a lexicalist theory--structure is determined chiefly by the interaction between highly articulated lexical entries and parameterised universal principles of grammatical well-formedness. The phrase structure rules are reduced to a small number of highly general and universally available phrase structure (or immediate dominance) schemata. The linguistic objects in HPSG (i.e., signs) are modelled using typed Feature Structures. non-transformational The theory posits the existence of a single stratum of linguistic representation with different levels of linguistic structure expressed as values of appropriate attributes. HPSG is and non-derivational--attributes in the linguistic structure are related using the notion of structure sharing, that is, token identity between substructures of a given structure, in accordance with lexical specifications or grammatical principles (or complex interactions between the two). HPSG doesn't make use of tree configurational notions (like c-command). The grammar is viewed as a declarative system of constraints which determine what the well-formed expressions of the language are. Because of the nature of typed feature structures, and more specifically, because of the monotonicity of the Unification operation, the order in which linguistic constraints are applied is irrelevant. Thus, HPSG is a competence model of language. HPSG is a very widespread grammatical framework among computational linguists. Implementations of HPSG grammars are naturally embedded within constraint-based, unification frameworks (see Unification Grammars).
- Pollard, C. and Sag, I., Head-Driven Phrase Structure Grammar
, The University of Chicago Press, Chicago, 1994.