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Head-driven Phrase Structure Grammar (HPSG)

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

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Head-driven Phrase Structure Grammar (HPSG)

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

  2. 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.

  3. 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.

  4. 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 dataccvoc • Figure 1: Subtypes of case in a Romanian grammar

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

  6. 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).

  7. 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.

  8. 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

  9. 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.

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