Head-driven Phrase Structure Grammar (HPSG) An integrated theory of natural language syntax and semantics

Definition HPSG is a ‘sign based’ grammar, where phonological, syntactic and semantic information is integrated into a formally precise description of linguistic objects using feature structures, developed by Ivan Sag and Carl Pollard in the mid 80s. Universal grammar: a) linguistic signs; b) combination principles.

Main features Features and values characterise linguistic objects; Structure sharing allows to say that certain values in a feature structure are identical; Valence information is represented in lists in a complex description of the head; Types allows for classification of (linguistic) objects.

Framework HPSG assumes features structures as models of linguistic objects. Feature structures are called AVM (Attribute Value Matrix); AVM consists of feature value pairs; The values can be atomic or feature descriptions; Every feature structure is of a certain type; Types are ordered in hierarchies ; Hierarchies have the most general type at the top and the most specific at the bottom; case nom gen dat acc voc Figure 1: Subtypes of case in a Romanian grammar

Attribute value matrice - AVM word PHON <‘talks’> synsem category HEAD verb CAT VALENCE C AT HEAD noun SUBJ ref-index SYNSEM PER 3rd CONT NUM sing COMP <> content CONT TALKER 1 1

AVM’s translation AVM for the word ‘talks’; The verb categorical information is divided into features that describe it, HEAD, and features that describe its arguments, VALENCE. Talks is a sign of type word with a head of type verb. Intransitive verb with no complement requires a subject that is a third person singular noun. The semantic value of the subject is co-indexed with the verb’s only argument (the individual doing the talking).

Motivations for HPSG Computer processable grammars that scale up and can be implemented; Most wide-spread grammatical framework employed in computational linguistics; A must for everyone working on natural language processing; Increased precision; Framework for integration; Psycholinguistic plausibility.

Implementations Various parser based on the HPSG formalism have been written, e.g. Enju Currently there are grammars for German, Mandarin, Chinese, 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; The Babel system, a system of analysing written language

Bibliography http://hpsg.stanford.edu http://ai.ato.ms/MITECS/Entry/green.html C Pollard, IA Sag - 1994 - books.google.com http://hpsg.fu-berlin.de/~stefan/Pub/hpsg-hsk.pdf http://cslipublications.stanford.edu/site/0226674479.shtml Carl Pollard, Ivan A. Sag (1987): Information-based Syntax and Semantics. Volume 1: Fundamentals. Stanford: CSLI Publications.