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, 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 (data type theory and knowledge representation) and uses Ferdinand de Saussure'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.
An HPSG grammar 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.
The basic type HPSG deals with is the sign. Words and phrases are two different subtypes of sign. A word has two features: [PHON] (the sound, the phonetic form) and [SYNSEM] (the syntactic and semantic information), both of which are split into subfeatures. Signs and rules are formalized as typed feature structures.
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).
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.
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On désigne par grammaire de dépendance une approche de la syntaxe fondée par Lucien Tesnière. Elle se distingue par la place centrale donnée à une structure hiérarchique, appelée Stemma par Lucien Tesnière, mais plus connue aujourd'hui sous le terme d’arbre de dépendance. L'arbre de dépendance est un arbre, au sens mathématique du terme, représentant les liens syntaxiques entre les mots d'une phrase. Les grammaires de dépendance ne réfèrent donc pas à un cadre théorique restreint, mais la notion de dépendance peut être explicite ou implicite dans la formalisation des règles syntaxiques.
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 the Chomsky hierarchy: context-sensitive grammars or context-free grammars. In a broader sense, phrase structure grammars are also known as constituency grammars. The defining trait of phrase structure grammars is thus their adherence to the constituency relation, as opposed to the dependency relation of dependency grammars.
HPSG (abréviation anglaise de head-driven phrase structure grammar, traduction française : grammaire syntagmatique guidée par les têtes) est, en linguistique, une théorie syntaxique. Son nom se réfère à la notion de tête, élément principal d'un syntagme. Comme la LFG, autre théorie syntaxique, il s'agit d'une grammaire d'unification : elle associe un attribut (ex. nombre) à une valeur (ex. pluriel), ce qui la rend adaptée au traitement automatique de la langue.
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