What is a typed feature structure?

It is a structured bundle of attribute-value pairs assigned a type, used in HPSG to represent all the phonological, syntactic, and semantic information about a word or phrase in one object. Types are organised in a hierarchy so that generalisations can be inherited.

Does HPSG use transformations?

No. HPSG is monostratal and non-derivational. There is a single level of representation, and dependencies that are handled by movement in transformational grammar are captured through features that are shared and passed along the structure.

Head-Driven Phrase Structure Grammar

Head-Driven Phrase Structure Grammar (HPSG) is a lexicalist, constraint-based theory in which words and phrases are modelled as typed feature structures combined by general schemata and principles.

Definition

Head-Driven Phrase Structure Grammar is a non-transformational theory of grammar that represents words and phrases as typed feature structures and characterises well-formedness through constraints, including principles that pass head features from a head to its projection.

Scope

This topic covers HPSG: its representation of linguistic objects as typed feature structures (signs), its use of unification and a type hierarchy, the head feature and other principles that govern combination, and its strongly lexicalist, non-derivational, surface-oriented character. It does not survey rival frameworks, which are treated in sibling topics.

Core questions

How are words and phrases represented as typed feature structures?
What role do unification and the type hierarchy play in combining structures?
How do principles such as the Head Feature Principle govern phrase formation?
How does a monostratal, constraint-based grammar handle phenomena treated by movement elsewhere?

Key concepts

typed feature structure
sign
unification
type hierarchy and inheritance
Head Feature Principle
valence and subcategorisation
monostratal grammar

Key theories

Signs as typed feature structures: The HPSG conception of every linguistic object as a sign, a typed feature structure pairing phonological, syntactic, and semantic information, organised in a type hierarchy with inheritance.
Constraint principles and unification: The use of general principles, such as the Head Feature Principle and the Valence Principle, together with unification, to license phrases without transformations, building on Generalized Phrase Structure Grammar.

History

HPSG grew out of the constraint-based tradition of Generalized Phrase Structure Grammar (Gazdar et al. 1985) and unification-based approaches. Pollard and Sag (1994) gave the framework its canonical statement, representing all linguistic information in typed feature structures. Sag, Wasow and Bender (2003) provided an accessible formal introduction. HPSG is widely used in computational linguistics for its declarative, implementable design.

Debates

Lexicalism and the locus of generalisation: How much grammatical generalisation should reside in a structured lexicon and type hierarchy versus in syntactic rules, an issue on which HPSG takes a strongly lexicalist position.

Key figures

Carl Pollard
Ivan Sag
Gerald Gazdar
Emily Bender

Seminal works

gazdar1985
pollardsag1994
sagwasowbender2003

Frequently asked questions

What is a typed feature structure?: It is a structured bundle of attribute-value pairs assigned a type, used in HPSG to represent all the phonological, syntactic, and semantic information about a word or phrase in one object. Types are organised in a hierarchy so that generalisations can be inherited.
Does HPSG use transformations?: No. HPSG is monostratal and non-derivational. There is a single level of representation, and dependencies that are handled by movement in transformational grammar are captured through features that are shared and passed along the structure.