What is HPSG?
Head-Driven Phrase Structure Grammar (HPSG) is a generative grammar theory. It was developed in the tradition of context-free phrase structure grammar and is the immediate successor to Generalized Phrase Structure Grammar (GPSG). It is called 'head-driven' in order to reflect the importance of information which is encoded in the lexical heads of syntactic phrases.
Properties of HPSG:
- highly lexicalized: the main information about linguistic relations is given in the lexical entries ('rich lexicon');
- sign-based: HPSG uses the sign (in the sense of Ferdinand de Saussure) to represent a linguistic form together with its meaning;
- non-derivational: a structure or representation is not derived by another through operations like transformation or move- (as in GB, for example). Instead, only the surface tree is generated;
- monostratal: phonology, syntax and semantics are represented in the same structure rather than on separate levels (as in GB);
- constraint-based: a structure is well-formed if and only if it satisfies all relevant constraints;
- linguistic information is organized via types, type hierarchies and constraint inheritance;
- to model linguistic objects, HPSG uses typed feature structures, i.e. each feature structure is relevant only for a given type.