Head-driven phrase structure grammar (HPSG) is a highly lexicalized, constraint-based grammar developed by Carl Pollard and Ivan Sag. It is a type of

phrase structure grammar The term phrase structure grammar was originally introduced by Noam Chomsky as the term for grammar studied previously by Emil Post and Axel Thue ( Post canonical systems). Some authors, however, reserve the term for more restricted grammars in t ...

, as opposed to a

dependency grammar Dependency grammar (DG) is a class of modern Grammar, grammatical theories that are all based on the dependency relation (as opposed to the ''constituency relation'' of Phrase structure grammar, phrase structure) and that can be traced back prima ...

, and it is the immediate successor to generalized phrase structure grammar. HPSG draws from other fields such as

computer science Computer science is the study of computation, information, and automation. Computer science spans Theoretical computer science, theoretical disciplines (such as algorithms, theory of computation, and information theory) to Applied science, ...

( data type theory and

knowledge representation Knowledge representation (KR) aims to model information in a structured manner to formally represent it as knowledge in knowledge-based systems whereas knowledge representation and reasoning (KRR, KR&R, or KR²) also aims to understand, reason, and ...

) and uses

Ferdinand de Saussure Ferdinand Mongin de Saussure (; ; 26 November 185722 February 1913) was a Swiss linguist, semiotician and philosopher. His ideas laid a foundation for many significant developments in both linguistics and semiotics in the 20th century. He is wi ...

's notion of the sign. It uses a uniform formalism and is organized in a modular way which makes it attractive for

natural language processing Natural language processing (NLP) is a subfield of computer science and especially artificial intelligence. It is primarily concerned with providing computers with the ability to process data encoded in natural language and is thus closely related ...

. An HPSG includes principles and grammar rules and

lexicon A lexicon (plural: lexicons, rarely lexica) is the vocabulary of a language or branch of knowledge (such as nautical or medical). In linguistics, a lexicon is a language's inventory of lexemes. The word ''lexicon'' derives from Greek word () ...

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. The basic type HPSG deals with is the sign.

Word A word is a basic element of language that carries semantics, meaning, can be used on its own, and is uninterruptible. Despite the fact that language speakers often have an intuitive grasp of what a word is, there is no consensus among linguist ...

s and

phrase In grammar, a phrasecalled expression in some contextsis a group of words or singular word acting as a grammatical unit. For instance, the English language, English expression "the very happy squirrel" is a noun phrase which contains the adject ...

s are two different subtypes of sign. A word has two features: '' HON' (the sound, the

phonetic Phonetics is a branch of linguistics that studies how humans produce and perceive sounds or, in the case of sign languages, the equivalent aspects of sign. Linguists who specialize in studying the physical properties of speech are phoneticians ...

form) and '' YNSEM' (the

syntactic In linguistics, syntax ( ) is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure (constituency ...

and

semantic Semantics is the study of linguistic Meaning (philosophy), meaning. It examines what meaning is, how words get their meaning, and how the meaning of a complex expression depends on its parts. Part of this process involves the distinction betwee ...

information), both of which are split into subfeatures. Signs and rules are formalized as typed feature structures.

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 matrices (AVMs). Pollard, Carl; Ivan A. Sag. (1994).
Head-driven phrase structure grammar
'. Chicago: University of Chicago Press. 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). "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. Signs of type ''phrase'' unify with one or more children and propagate information upward. The following AVM encodes the 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. 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.

Implementations

Various parsers based on the HPSG formalism have been written and optimizations are currently being investigated. An example of a system analyzing German

sentences The ''Sentences'' (. ) is a compendium of Christian theology written by Peter Lombard around 1150. It was the most important religious textbook of the Middle Ages. Background The sentence genre emerged from works like Prosper of Aquitaine's ...

is provided by the

Freie Universität Berlin The Free University of Berlin (, often abbreviated as FU Berlin or simply FU) is a public university, public research university in Berlin, Germany. It was founded in West Berlin in 1948 with American support during the early Cold War period a ...

. In addition the CoreGram project of the Grammar Group of the

provides open source grammars that were implemented in the TRALE system. Currently there are grammars for German, Danish,

Mandarin Chinese Mandarin ( ; zh, s=, t=, p=Guānhuà, l=Mandarin (bureaucrat), officials' speech) is the largest branch of the Sinitic languages. Mandarin varieties are spoken by 70 percent of all Chinese speakers over a large geographical area that stretch ...

, Maltese, and Persian 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 Deep Linguistic Processing with HPSG - INitiative (DELPH-IN) is a collaboration where computational linguists worldwide develop natural language processing tools for deep linguistic processing of human language. The goal of DELPH-IN is to combine ...

). Wide-coverage grammars of English, German, and Japanese are available under an open-source license. These grammars can be used with a variety of inter-compatible open-source HPSG parsers: LKB, PET, Ace, and ''agree''. All of these produce semantic representations in the format of “Minimal Recursion Semantics,” MRS. The declarative nature of the HPSG formalism means that these computational grammars can typically be used for both

parsing Parsing, syntax analysis, or syntactic analysis is a process of analyzing a String (computer science), string of Symbol (formal), symbols, either in natural language, computer languages or data structures, conforming to the rules of a formal gramm ...

and generation (producing surface strings from semantic inputs). Treebanks, also distributed by

, 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 Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

.Tsuji Lab: Enju parser home page
(retrieved Nov 24, 2009)

References

External links

* Online proceedings of the annual HPSG conference https:// proceedings.hpsg.xyz/issue/archive
Ohio State HPSG homepage

International Conference on Head-Driven Phrase Structure Grammar

DELPH-IN network for HPSG grammar development

* ttp://hpsg.fu-berlin.de/HPSG-Bib/ Bibliography of HPSG Publications
LaTeX package for drawing AVMs
– includes documentation {{DEFAULTSORT:Head-Driven Phrase Structure Grammar Generative linguistics Grammar frameworks Syntactic theories

Sample grammar

Implementations

See also

References

Further reading

External links