Functional Unification Grammar Revisited

Functional Unification Grammar Revisited Kathleen R. McKeown and Cecile L. Paris Department of Computer Science 450 Computer Science Columbia University New York, N.Y. 10027 MCKEOWN@CS.COLUMBIA.EDU CECIL~@CS.COLUMBIA.EDU Abstract In this paper, we show that one benefit of FUG, the ability to state global conslralnts on choice separately from syntactic rules, is difficult in generation systems based on augmented context free grammars (e.g., Def'mite Clause Cn'anmm~). They require that such constraints be expressed locally as part of syntactic rules and therefore, duplicated in the grammar. Finally, we discuss a reimplementation of lUg that achieves the similar levels of efficiency as Rubinoff's adaptation of MUMBLE, a detcrministc language generator. 1 Introduction Inefficiency of functional unification grammar (FUG, [5]) has prompted some effort to show that the same benefits offered by FUG can be achieved in other formalisms more efficiently [3; 14; 15; 16]. In this paper, we show that one benefit of FUG, the ability to conciselyl state global constraints on choice in generation, is difficult in other formalhms in which we have written generation systems. In particular, we show that a global constraint can be stated separately from syntactic rules in FUG, while in generation systems based on augmented context free ~g~nunars (e.g., Definite Clause Cn'amma~ (DCG, [13])) such consWaints must be expressed locally as part of syntactic rules and the~=for¢, duplicated in the grammar. Finally, we discuss a reimplementation of lUG in TAILOR [11; 12] that achieves the si.m/l~r leveLs of efficiency as Rubinoff's adaptation [16] of MUMBLE [7], a deterministc language generator. 1.1 Statement of Constraints Language generation can be viewed primarily as a problem of choice, requiring decisions about which syntactic structures best express intent. As a result, much research in language generanon has focused on identi~ing conswaints on choice, and it is important to be able to represent these constraints clearly and efficiently. In this paper, we compare the representation of constraints in FUG with their repn:sentation in a DCG generation system [3]. We are interested in representing functional constraints on syntactic sWacture where syntax does not fully restrict expression; that is, conswaints other than those coming from syntax. We look at the representation of two specific constraints on syntactic choice: focus of attention on the choice of sentence voice and focus of attention on the choice of simple versus complex sentences. We claim that, in a lUG, these constraints can be stated separately from rules dictating syntactic structure, thus leading to simplicity of the granunar since the constraints only need to be stated once. This is possible in FUG because of unification and the ability to build constituent structure in the grammar. In contrast, in a DCG, constraints must be stated as part of the individual grammar rules, resulting in duplication of a constraint for each syntactic rule to which it applies. 1.2 Passive/Active Constraint Focus of attention can determine whether the passive or active voice should be used in a sentence [8]. The constraint dictates that focused information should appear as surface subject in the sentence. …

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