Integrating Syntactic and Prosodic Information for the Efficient Detection of Empty Categories

Integrating Syntactic and Prosodic Information for the Efficient Detection of Empty Categories Anton Batliner l, Anke Feldhaus ~, Stefan GeiBler t, Andreas KieBling*, Tibor Kiss ~, Ralf Kompe*, Ehnar N~ith* I,MU Miinch(.n t IBM l)eutschl~nd lnforma.tionssysteme ~ FAll ti',rla.ngen-Niirnl)erg * lnstitut f. I)eutsche Philologie Inst. f. Logik und l,inguistik 1,ehrstuhl f. Mustererk¢.tmung Sehellingstr. 3 V~tngerowstr. 18 Martensstr. 3 D-80799 Miinchen 11)-69115 IIeidelberg 1)-91058 ]';rlangen Abstract We describe a number of experiments that demonstrate the usefulness of prosodic information for a processing module which parses spoken utterances with a feature-based grammar employing empty categories. We show that by re- quiring certain prosodic properties from those positions in the input, where the presence of an empty category has to be hypothesized, a derivation can be accom- plished more efficiently. The approach has been implemented in the machine translation project VEItBMOBII, and re- sults in a significant reduction of the work-load for the parser t. 1 Introduction In this paper we describe how syntactic and prosodic information interact in a translation module for spoken utterances which tries to meet the two - often conflicting - main objectives, the implementation of theoretically sound solutions and efficient processing of tile solutions. As an analysis which meets the first criterion but seemingly fails to meet the second one, we take an analysis of the German clause which relies on traces in verbal head positions in the framework of Head-driven Phrase Structure Grammar (llt'sG, cf. (Pollard&Sag, 1994)). The methods described in this paper have been implemented as part of the IBM-SynSem.. Module and the FAU-Erlangen/LMU-Munich- Prosody-Module in the MT project Vl,;ltHMOmI, (of. (Wahlster, 1993)) where spontaneously spo- ken utterances in a negotiation dialogue are trans- lated. In this system, an lh's(~ is processed by a bottom-up chart parser that takes word lattices as tThis work was partiMly funded by the Gc,- Imtn Vedcral Ministry for Research and Technology (BMIW) in the framework of the Verbmobil Project under (~r~nt ~(11 IV 101 V (Verbmobil). Tim rt:spon- slbility for the contents of this study lies with the aa,- thors. its input. The output of the parser is the seman- tic representation for the best string hypothesis in the lattice. It is our main result that prosodic informa- tion can be employed in such a system to de- termine possible locations for empty elements in tile input. Rather than treating prosodic informa- tion as virtual input items which have to match an appropriate category in tile grammar rules (Bear&Price, 1990), or which by virtue of being 'unknown' in the grammar force the parser to close off the current phrase (Marcus&Hindle, 1990), our parser employs prosodic information as affecting the postulation of empty elements. 2 An HI'sG Analysis of German Clause Structure [[PSG makes crucial use of "head traces" to ana- lyze the verb-second (V2) phenomenon pertinent in German, i.e. the fact that finite verbs appear in second position in main clauses but in final posi- tion in subordinate clauses, as exemplified in (la) and (lb). 1. (a) Gestern reparierte er …

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