Tree Unification Grammar

TREE UNIFICATION GRAMMAR Frdd Popowich School of Computing Science Simon Fraser University Bumaby, B.C. CANADA V5A 186 ABSTRACT Tree Unification Grammar is a declarative unification-bas~:l linguistic framework. The basic grammar stmaures of this framework are partial descriptions of trees, and the framework requires only a single grammar rule to combine these partial descriptions. Using this framework, constraints associated with various linguistic phenomena (reflexivisation in particular) ~ be stated succinctly in the lexicon. INTRODUCTION There is a mind in uni~ca~on-based grammar formalisms towards using a single grammar stmctme to contain the phonological, syntactic and semantic information associated with a linguistic expression. Adopting'the terminology used by Pollard and Sag (1987), this grammar structure is called a sign. Grammar rules, guided by the syntactic information contained in signs, are used to derive signs associated with complex expressions from those of their constituent expressions. The relationship between the signs and the complex signs derived from grammar rule application can be expressed in derivationai structures. These structures both explicitly illustrate relations that are implicit in the syntax of the signs and express relations that are present in the grammar roles. Tree unification grammar (TUG) is a formalism which uses function-argument (FA) specif~ationa as its primary grammar structures. These specifications resemble partially specified derivational stmcmn~ of sign-based formalisms like head-driven phrase structure grammar (HPSG) (Pollard and Sag, 1987) and unification categorial grammar (UCG) (7_,eevat, Klein and Calder, 1987). TUG uses FA specifications as lexical entries and possesses a single grammar rule which combines these specifications to obtain a specification for the complex expression being analysed. The use of FA specifications allows generafisations that are often captured in grammar rules to be captured in the lexicon. MOTIVATION The development of TUG was a consequence of investigating extensions to the UCG framework. As described by Zeevat, Kh~,, .-d Calder (1987), UCG is a grammar formalism which combines SOme of the notiow~s of categorial grammar with those of unification-based formalisms like HPSG and PATR-II (Shicber el.at., 1983). The nsse.t~h .~tM~,,~d in this lmq~r wu ~ o~ at the Univmlity of EdlnbeJqth under the rapport of • BrifiJh C,~-,'~weallh Scholmhlp and at 51hUm FmJ~ Uui~ky unde* ms Advmu~ Synmll Imti~e ~ Fellov~hip. Special thar, Jo to the Omm: f~ Systmm Scknm md zhe L*bm.atm.y for ~ r md Rnem~ at Simon Fruer Unlve~izy fro. additkmal ml~pe~ I would I.'%-.. to t/rank Dm~ P~ md Om ACL mvi~a for thmt ¢,omm~B ,~4 m I l ~ Like HPSG, the fundamental construction used in UCG is the sign. A UCG sign has auributes for phonology, category, semantics and order. Consider the sign for the expression Mary walks shown in (I). (I) Mary-walks smt[f'm] [eli [[fllmary(fl), [el]walk(el,fl)] The phonology attribute of this sign (ie. Mary-walks) represents a phonological specification of the linguistic expression associated with the sign. For our needs we will use a simple sequence of words separated by hyphens. The category structure of a sign is very similar to that used by categorial grammar. There are three primitive categories, namely sent, …

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