Editing Head-driven phrase structure grammar (section)

{{Short description|Framework for describing natural languages' syntax}}
'''Head-driven phrase structure grammar''' ('''HPSG''') is a highly lexicalized, [[constraint-based grammar]]<ref>{{cite web|title=HPSG|url=https://www.acsu.buffalo.edu/~rchaves/hpsg.html}}</ref>
<ref name="handbook">{{cite book
| veditors = 	 Müller S, Abeillé A, Borsley RD, Koenig JP   
| title =Head-Driven Phrase Structure Grammar: The handbook 
| place = Berlin
| publisher = Language Science Press
| date = 2021
| format = pdf
| url = http://langsci-press.org/catalog/book/259
| doi = 10.5281/zenodo.5543318 
| doi-access=free
| isbn = 978-3-96110-255-6  
| last1 =Müller 
| first1 =Stefan 
| last2 =Abeillé 
| first2 =Anne 
| last3 =Borsley 
| first3 =Robert D. 
| last4 =Koenig 
| first4 =Jean-Pierre 
}}</ref>
developed by [[Carl Pollard]] and [[Ivan Sag]].<ref>Pollard, Carl, and Ivan A. Sag. 1987. Information-based syntax and semantics. Volume 1. Fundamentals. CLSI Lecture Notes 13.</ref><ref name="Pollard"></ref> It is a type of [[phrase structure grammar]], as opposed to a [[dependency grammar]], and it is the immediate successor to [[generalized phrase structure grammar]]. HPSG draws from other fields such as [[computer science]] ([[type system|data type theory]] and [[knowledge representation]]) and uses [[Ferdinand de Saussure]]'s notion of the [[sign (linguistics)|sign]]. It uses a uniform formalism and is organized in a modular way which makes it attractive for [[natural language processing]].

An HPSG includes principles and grammar rules and [[lexicon]] entries which are normally not considered to belong to a grammar. The formalism is based on lexicalism. This means that the lexicon is more than just a list of entries; it is in itself richly structured. Individual entries are marked with types. Types form a hierarchy.  Early versions of the grammar were very lexicalized with few grammatical rules (schema).  More recent research has tended to add more and richer rules, becoming more like [[construction grammar]].<ref>Sag, Ivan A. 1997. [https://www.academia.edu/download/31190371/10.1.1.51.7483.pdf English Relative Clause Constructions]{{dead link|date=July 2022|bot=medic}}{{cbignore|bot=medic}}.  Journal of Linguistics . 33.2: 431-484</ref>

The basic type HPSG deals with is the sign. [[Word]]s and [[phrase]]s are two different subtypes of sign. A word has two features: ''[PHON]'' (the sound, the [[Phonetics|phonetic]] form) and ''[SYNSEM]'' (the [[Syntax|syntactic]] and [[Semantics|semantic]] information), both of which are split into subfeatures. Signs and rules are formalized as [[Type theory|typed]] [[feature structure]]s.