Planning word-order dependant focus assignments

Word order and accent placement are the primary linguistic means to indicate focus/background structures in German. This paper presents a pipelined architecture for the generation of German monologues with contextually appropriate word order and accent placements for the realization of focus/background structures. Our emphasis is on the sentence planner that extends the respective propositional contents with discourse-relational features and decides which part will be focused. Such an enriched semantic input for an HPSG-based formulator allows word order variations and the placement of prenucleus and nucleus accents. Word order is realized by grammatical competition based on linear precedence (LP) rules which are based on the discourserelational features. Accent placement is realized by a syntax-driven focus principle that determines the focus exponent and possible bearers of prenucleus accents within the syntactically realized focus, the so-called focus domain. 1 F o c u s a n d w o r d o r d e r d e t e r m i n a t i o n a s s e n t e n c e p l a n n i n g t a s k s This paper addresses aspects of the control of intonation belonging to the area of sentence planning [Beale et al., 1998: Wanner and Hovy, 1996]. In many languages, intonation can reflect pragmatically motivated conceptual decisions. In particular, focus/background structures (FBSs) reflect the speaker's beliefs of the listener's information state. Since FBSs are realized in German primarily by word order dependent accent placements, focus planning and word order determination are subtasks of sentence planning. Due to the complex interactions anaong the various subtasks of sentence planning [Hovy and Wan* The research repor ted in th is paper is funded by the DFG ( G e r m a n Science Founda t ion) in the pr ior i ty program "Language P roduc t ion" under gran t l ie 146T/3-I. The authors would like to thank the th ree anonymous referees for helpful c o m m e n t s and suggest ions . All remain ing mis takes are, of c o u r s e . O U F o ~ v n . her, 1996] proposed a blackboard-based sentence planner instead of a pipelined architecture. However, we will demonstrate as a byproduct of our approach to focus planning that in some cases the complexity of interactions can be realized by a traditional top-down expansion process. The intertwined clause-internal organization of focus planning and word order determination for the realization of FBSs in German is obtainable by hierarchical planning. In what follows, we will first give examples of the interplay of focus and word order in German. We will present the architecture of our NLG system that realizes FBSs and describe in more detail hierarchical sentence planning for FBSs. By means of some examples we are finally showing how word order dependent focus assignment works. 2 T h e i n t e r p l a y o f f o c u s a n d w o r d