Editing Head-driven phrase structure grammar

{{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.

==Sample grammar==
HPSG generates strings by combining signs, which are defined by their location within a type hierarchy and by their internal feature structure, represented by [[attribute value matrix|attribute value matrices]] (AVMs).
<ref name="Pollard">Pollard, Carl; Ivan A. Sag. (1994). ''[https://books.google.com/books?id=Ftvg8Vo3QHwC Head-driven phrase structure grammar]''. Chicago: University of Chicago Press.</ref><ref>Sag, Ivan A.; Thomas Wasow; & Emily Bender. (2003). ''Syntactic theory: a formal introduction''. 2nd ed.  Chicago: University of Chicago Press.</ref> Features take types or lists of types as their values, and these values may in turn have their own feature structure. Grammatical rules are largely expressed through the constraints signs place on one another. A sign's feature structure describes its phonological, syntactic, and semantic properties. In common notation, AVMs are written with features in upper case and types in italicized lower case. Numbered indices in an AVM represent token identical values.

In the simplified AVM for the word (in this case the verb, not the noun as in "nice walks for the weekend") "walks" below, the verb's categorical information (CAT) is divided into features that describe it (HEAD) and features that describe its arguments (VALENCE).

[[Image:Walks-avm.png|AVM for walks|center]]

"Walks" is a sign of type ''word'' with a head of type ''verb''. As an intransitive verb, "walks" has no complement but requires a subject that is a third person singular noun. The semantic value of the subject (CONTENT) is co-indexed with the verb's only argument (the individual doing the walking). The following AVM for "she" represents a sign with a SYNSEM value that could fulfill those requirements.

[[Image:She-avm.png|center]]

Signs of type ''phrase'' unify with one or more children and propagate information upward. The following AVM encodes the [[ID/LP grammar|immediate dominance rule]] for a ''head-subj-phrase'', which requires two children: the head child (a verb) and a non-head child that fulfills the verb's SUBJ constraints.

[[Image:Head-subj-avm.png|center]]

The end result is a sign with a verb head, empty subcategorization features, and a phonological value that orders the two children.

Although the actual grammar of HPSG is composed entirely of feature structures, linguists often use trees to represent the unification of signs where the equivalent AVM would be unwieldy.

[[Image:Head-subj-tree.png|center]]

==Implementations==
Various [[parsing|parsers]] based on the HPSG formalism have been written and optimizations are currently being investigated. An example of a system analyzing [[German language|German]] [[Sentence (linguistics)|sentences]] is provided by the [[Freie Universität Berlin]].<ref>[http://hpsg.hu-berlin.de/~stefan/Babel/Interaktiv/ The Babel-System: HPSG Interactive<!-- Bot generated title -->]</ref> In addition the CoreGram<ref>[http://hpsg.hu-berlin.de/Projects/CoreGram.html The CoreGram Project]</ref> project of the Grammar Group of the [[Freie Universität Berlin]] provides open source grammars that were implemented in the TRALE system. Currently there are grammars for [[German language|German]],<ref>[http://hpsg.hu-berlin.de/Fragments/Berligram/ Berligram]</ref> [[Danish language|Danish]],<ref>[http://hpsg.hu-berlin.de/Fragments/Danish/ DanGram]</ref> [[Mandarin Chinese]],<ref>[http://hpsg.hu-berlin.de/Fragments/Chinese/ Chinese]</ref> [[Maltese language|Maltese]],<ref>[http://hpsg.hu-berlin.de/Fragments/Maltese/ Maltese]</ref> and [[Persian language|Persian]]<ref>[http://hpsg.hu-berlin.de/Fragments/Persian/ Persian]</ref> that share a common core and are publicly available.

Large HPSG grammars of various languages are being developed in the Deep Linguistic Processing with HPSG Initiative ([[DELPH-IN]]).<ref>[http://www.delph-in.net/ DELPH-IN: Open-Source Deep Processing]</ref> Wide-coverage grammars of English,<ref>[https://archive.today/20120723212352/http://www.delph-in.net/erg/ English Resource Grammar and Lexicon<!-- Bot generated title -->]</ref> German,<ref>[https://web.archive.org/web/20061205202742/http://gg.dfki.de/ Berthold Crysmann<!-- Bot generated title -->]</ref> and [[Japanese language|Japanese]]<ref>[http://www.delph-in.net/jacy JacyTop - Deep Linguistic Processing with HPSG (DELPH-IN)<!-- Bot generated title -->]</ref> are available under an open-source license. These grammars can be used with a variety of inter-compatible open-source HPSG parsers: [[Linguistic Knowledge Builder|LKB]], PET,<ref>[http://heartofgold.dfki.de/PET.html DELPH-IN PET parser]</ref> Ace,<ref>[http://sweaglesw.org/linguistics/ace/ Ace: the Answer Constraint Engine]</ref> and ''agree''.<ref>[http://www.agree-grammar.com/ agree grammar engineering]</ref> All of these produce semantic representations in the format of “Minimal Recursion Semantics,” MRS.<ref>Copestake, A., Flickinger, D., Pollard, C., & Sag, I. A. (2005). [https://link.springer.com/article/10.1007/s11168-006-6327-9 Minimal recursion semantics: An introduction]. Research on Language and Computation, 3(2-3), 281-332.</ref> The declarative nature of the HPSG formalism means that these computational grammars can typically be used for both [[parsing]] and generation (producing surface strings from semantic inputs). Treebanks, also distributed by [[DELPH-IN]], are used to develop and test the grammars, as well as to train ranking models to decide on plausible interpretations when parsing (or realizations when generating).

''Enju'' is a freely available wide-coverage probabilistic HPSG parser for English developed by the Tsujii Laboratory at [[The University of Tokyo]] in [[Japan]].<ref>[http://www-tsujii.is.s.u-tokyo.ac.jp/enju/ Tsuji Lab: Enju parser home page] {{webarchive|url=https://web.archive.org/web/20100307175009/http://www-tsujii.is.s.u-tokyo.ac.jp/enju/ |date=2010-03-07 }} (retrieved Nov 24, 2009)</ref>

==See also==
* [[Lexical-functional grammar]]
* [[Minimal recursion semantics]]
* [[Relational grammar]]
* [[Situation semantics]]
* [[Syntax]]
* [[Transformational grammar]]
* Type Description Language

==References==
{{reflist}}

==Further reading==
* Stefan Müller, Anne Abeillé, Robert D. Borsley, Jean-Pierre Koenig (eds.) (2024): ''[https://doi.org/10.5281/zenodo.5543317 Head-Driven Phrase Structure Grammar: The handbook]''. (= Empirically Oriented Theoretical Morphology and Syntax; 9). Berlin: Language Science Press, 2nd edition, ISBN 978-78-3-98554-111-9
* [[Carl Pollard]], [[Ivan Sag|Ivan A. Sag]] (1987): ''Information-based Syntax and Semantics. Volume 1: Fundamentals''. Stanford: CSLI Publications.
* [[Carl Pollard]], [[Ivan Sag|Ivan A. Sag]] (1994): ''Head-Driven Phrase Structure Grammar''. Chicago: University of Chicago Press. ([https://web.archive.org/web/20040107095004/http://cslipublications.stanford.edu/site/0226674479.html])
* [[Ivan Sag|Ivan A. Sag]], [[Thomas Wasow]], [[Emily M. Bender]] (2003): ''Syntactic Theory: a formal introduction, Second Edition''. Chicago: University of Chicago Press. ([https://web.archive.org/web/20031002161010/http://cslipublications.stanford.edu/site/1575864002.html])
* {{cite encyclopedia
 |last         = Levine
 |first        = Robert D.
 |author-link   = Robert D. Levine
 |author2      = W. Detmar Meurers
 |editor       = Keith Brown
 |encyclopedia = Encyclopedia of Language and Linguistics
 |title        = Head-Driven Phrase Structure Grammar: Linguistic Approach, Formal Foundations, and Computational Realization
 |url          = http://www.ling.ohio-state.edu/~dm/papers/ell2-hpsg.pdf
 |edition      = second
 |year         = 2006
 |publisher    = Elsevier
 |location     = Oxford
 |access-date   = 2008-03-07
 |archive-url   = https://web.archive.org/web/20080905201034/http://www.ling.ohio-state.edu/~dm/papers/ell2-hpsg.pdf
 |archive-date  = 2008-09-05
 |url-status      = dead
}}
* {{cite journal
 | last = Müller
 | first = Stefan
 | author-link = Stefan Müller (linguist)
 | title = Unifying Everything: Some Remarks on Simpler Syntax, Construction Grammar, Minimalism and HPSG
 | url = http://hpsg.fu-berlin.de/~stefan/Pub/unifying-everything.html
 | year = 2013
 | journal = Language
 | volume = 89
 | issue = 4
 | pages = 920–950
 | doi = 10.1353/lan.2013.0061
 | s2cid = 55298660
 | access-date = 2013-07-12
 | archive-date = 2017-02-02
 | archive-url = https://web.archive.org/web/20170202115006/http://hpsg.fu-berlin.de/~stefan/Pub/unifying-everything.html
 | url-status = dead
 | url-access = subscription
 }}

==External links==
* Online proceedings of the annual HPSG conference https:// proceedings.hpsg.xyz/issue/archive
* [http://www.ling.ohio-state.edu/research/hpsg/ Ohio State HPSG homepage]
* [http://www.essex.ac.uk/linguistics/external/HPSG/ International Conference on Head-Driven Phrase Structure Grammar]
* [http://www.delph-in.net/ DELPH-IN network for HPSG grammar development]
* [https://web.archive.org/web/20120204060804/http://emsah.uq.edu.au/linguistics/Working%20Papers/ananda_ling/HPSG_Summary.htm Basic Overview of HPSG]
* [http://stellar.mit.edu/S/course/24/fa03/24.960/index.html Comparison of HPSG with alternatives, and a historical perspective]
* [http://hpsg.fu-berlin.de/HPSG-Bib/ Bibliography of HPSG Publications] {{Webarchive|url=https://web.archive.org/web/20120217011304/http://hpsg.fu-berlin.de/HPSG-Bib/ |date=2012-02-17 }}
* [http://nlp.stanford.edu/~manning/tex/ LaTeX package for drawing AVMs] – includes documentation

{{DEFAULTSORT:Head-Driven Phrase Structure Grammar}}
[[Category:Generative linguistics]]
[[Category:Grammar frameworks]]
[[Category:Syntactic theories]]