Basic properties and elements

Head-Driven Phrase Structure Grammar (HPSG) is a declarative and monostratal
version of Generative Grammar, in which linguistic expressions have a single
relatively simple constituent structure. It seeks to develop detailed formal analyses
using a system of types, features, and constraints. Constraints on types of
lexicalsign are central to the lexicon of a language and constraints on types of phrase
are at the heart of the syntax, and both lexical and phrasal types include
semantic and phonological information. Different versions of the framework have been
developed, including versions in which constituent order is a reflection not of
constituent structure but of a separate system of order domains, and the Sign-Based
Construction Grammar version, which makes a fundamental distinction between
signs of various kinds and the constructions which license them.