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<Paper uid="C94-1058">
  <Title>DEFAULT HANDLING IN INCREMENTAL GENERATION</Title>
  <Section position="4" start_page="359" end_page="360" type="metho">
    <SectionTitle>
3 EXAMPLES OF DEFAULTS
IN VM-GEN
</SectionTitle>
    <Paragraph position="0"> The adaptation of our general discussion of default handling to the system VM-CEN not only provides concrete examples for the reader but also shows that a homogeneous combination of default handling, regula.r processing, and utterance repair is possible.</Paragraph>
    <Paragraph position="1"> The syntactic generator VM-GI'~N is a further development of TA G-G E N (Kilger, 19!)4) within the fi-amework of VERBMOBIL, a speech-to-speech translation system. Its usefulness for simultaneous interpretation results from its incremental and pa'rallel style of processing. VM-GEN is able to consume input increinents of varying size. q'hese, increments describe lexical items or semantic relations between them. Single input increments are handed over to objects of a distril)uted parallel system, each of which tries to verbalize the structure that results from the corresponding input increment. VM-O,\]'~N uses ml extension of Tree Adjoining Gra'm'mct'rs (TACs, c\['. (aoshi, 1985)) as its syntactic representation formalism that is not only adequate for Ihe description of natura.1 language hut also supports incremental genera.lion (I(ilger aml Finkler, 1994).</Paragraph>
    <Paragraph position="2"> In the following, we iul;roduce examl)h:'s for default processing triggered during the (lerman inflection process in VM-GI'2N to suhstantiate tile global statements made in sec~ Lion 2. Inflection uses some synta.cLic properties of an element to compute its morphological form. This information has partly t:o be specified in the input (e.g., the numl)er for a noun) and is partly inherited fi'om other elrlf some phrases inllueneed by defaull.s have already been verbalized, the eft'eel; of verl~alizaLion can be cancelled by using repair words like &amp;quot;oops&amp;quot; or &amp;quot;sol ry&amp;quot; when starting t, he modified utt.erance.</Paragraph>
    <Paragraph position="3"> ements (e.g., tile number for a verb or tile case for a noun). The two reasons for missing information necessitate different methods of treatment which nevertheless both can uniformly be integrated into regular processing.</Paragraph>
    <Paragraph position="4"> If information of the first type is missing (e.g., because of problems during analysis, see section 1), an assuml~tion can be made locally by simulating the respective part of the input.</Paragraph>
    <Paragraph position="5"> The default for missing number information in VM-CIBN would look as follows: \[ (e*.I(OBJ,=N) (I;,'NTITY OB.I \] ( ....... ber(OBd)=NIL) =&gt; ('au',,dm,' sg)) ; 0.8 8 The set of default preconditions is applied to all 'j objects (OB.1) of VM-GEN in order to Lest the kind of underspecification ('number' in the example). The default body introduces a new value (sg) by creating an input increment as a. default. The test for coincidence with the input-licensed value is realized by a comparison in the objects of VM-CEN.</Paragraph>
    <Paragraph position="6"> There is a. uuique association of input increments and objocts of VM-(~EN (OBJ is used as identifier)l:hat allows for translating an input mo(lifica.l:ion into a. modification of the state of the respective object. In ease of contradictions the dofa.ult and all default-caused decisions are revised m (see below).</Paragraph>
    <Paragraph position="7"> Making a.n assumption can Im influenced by .qlolml constra.ints. An example, which is well studied in psycholinguistics, is the utterance o\[&amp;quot; a noun before the vc~'l~ has been chosen.</Paragraph>
    <Paragraph position="8"> If, e.g., the nol.lll &amp;quot;Besucher&amp;quot; (l&amp;quot;,nglish: &amp;quot;visitOl&amp;quot;') iS I':.IIOWll t(} I)e the agellt of all action, il: nlay Im uttered as sul@-ct in the first posit, ion of the sentence l~y del'a.ult. This treatretail, l)reSUl)l)OSes I,lle clloi(;e of a ~(htmmy' v(.'rl), which at least sul)cal,egorizes a subject a.nd has active voice 11. The use of a dummy ~'ENTITY' introduces information al)ouL a lexical item. For reasons of inerementaliLy, there may be several l~,NTlq'Y--lmCkages specified for the same item which are composed to reeeiw.' I,he global itl\['ormM;iOl|. For certainly values, we use wdues tmt.ween O and I, where I means high reliability.</Paragraph>
    <Paragraph position="9"> ~lhl the ael.ual imldementat.ion we preselect candidates with missing values fi~r re;tsolls of efficiency. ldegl,'or ongoing work on repair in VM-(IlCN see (Finkler, 1994).</Paragraph>
    <Paragraph position="10"> l lThis kind of expansion is called &amp;quot;provisional upward expansioll&amp;quot; by (I)e SmedL, 1990).</Paragraph>
    <Paragraph position="11">  verb and an underspecified verbal structure, the NP is integrated inl,o allows for a shnl)le global test tlmt rules out the same case wdue assignment to different NP coml)h'ment:s as it is required for most of the C, erman verbs.</Paragraph>
    <Paragraph position="12"> This rule is represented in the grammar as a p~rt of the description of subcategorizal:ion fl'ames for verbs. For reasous of homogoue-ity we use the information stored in the syntactic knowh'Age source, s of VM- G\]';N for ex~ pressing syntactic constraints during default handling as well. 'Fit(', adwmtage of this approach is, that processing is continued iu a consistent way, which eases the introduction of the input--licensed wdue. One default for choosing a missing case-wdue ix specified as lbllows:</Paragraph>
    <Paragraph position="14"> The default preconditions of l,he rule characterize a sit;mttion where an object (O1LI) con.</Paragraph>
    <Paragraph position="15"> tains no information about the case \]&gt;llt ideutifies the input category as'N' for noun. Furthermore, the semantic fuuction of l;\]w o\])jecl: is specified as 'a.gent ~ but no verb deIim'(l yot (le,nma(h,,aa(Or J))=Nlr0 i,, lte.(t (,,ject. That is why, the N--object cannot inherit a case value and also does not know whether it is allowed to occupy the f'ront position ilt the utterance.</Paragraph>
    <Paragraph position="16"> \]'3valuating the (l('faull; body, I.he s.ysl.(.lll creates a V-object OILI'. On the basis of the input ildbrma.tion in (I.;NTrI'Y ()ILl'...) it chooses a lllillilllal sylll;actic sI;rllCtllre \['roHl the inheritance net o\[' the grammar, thai. just desribes ~t verb category without conclel;c filler (a dummy verb) plus a subject cmnpleuwnt and active voice for the verbM phrase. Now, the N-strucl;ure is com_bilwd with the V. strm:ture of the introduced V-ol)jecl. its dut'iug uof real processing. Therefore, the case va.llle cau be inherit(xl. Additionally, the first posil:iou 12'I/,ELtVFION' inl.l'oduces the specitical.iou of a relation bel.ween two \]exi(:al ii.enas whMl are ident.ified by the names of their objects.</Paragraph>
    <Paragraph position="17"> can be a.ssigne, d t,o Lhe subject which can be uttered now.</Paragraph>
    <Paragraph position="18"> Tile basic VM GI';N module provide.s re~ pair strategies in order to allow for tile specificatiou of additions, modifications and deletions o\[' input \]llCl'el'l/(Hlts, i,e. 1 t;o lilodet it flexible input inl:er\['a.ce. Throe fea, tures o\[' the system are lmsicMly used for repair: Fh'st, input illCrelllelitS are uuiquely associated with objects of VM-.(IEN, so that input modifications can Im translated into modifications of the objects' states. Sccoud, each modification C' an object's state makes it compare new and old information. Iu case of a difference, the modified parts a.re sent to all concerned objecl:s. Third, the del)eudency relations tha.t determine l, he communi(:ation links between objects allow for a, hierarchical orgaIfization of tile olLiccts, which ix the, basis \[br synchrouizing repair.</Paragraph>
    <Paragraph position="19"> A repair must be triggered in the exam-pie described abovo if, e.g., a verb wil.h wfice passive ix actually specified, in this case, the it~al)l)iug o1' tlm selnaut:ic role 'agent' I;o tim sylkl:acth: \['uuction 'subject' is revised. The ;igell\[; IIOW \]lit.S to \])e realized as part of a &amp;quot;you&amp;quot; phrase, e.g. &amp;quot;dieser Tel'rain wh'd yon dcm lh:mwhc'r gewiiuscht.&amp;quot; (word-for-word: &amp;quot;this date is whished b':l lhc visilor (dative ob.iect)&amp;quot;). F'urthermore, the object checks wlmtlwr the previously uttered part of the seul.em'e iuch|des some of the revised material (i.e., whether the ol@~ct itsel\[' has lmrticilmted hi littering). I\[' this is the case, it seuds an error message Itl~ 1.o tim Ul)l)ermost object C' the hierarchy l:llat actually is engaged in uH.crillp;. Tills o\[,jecl, is aide to synchronize global repair, lip to now, we just realized a simple tel)air stra.i:egy that consists of repeat;ing the concerned 1)ari:s el the utterance, e.g. &amp;quot;der Besucher ...fih ...dieser Terrain wird yon dcm l~e.~'twhc'r gewfinscld?'.</Paragraph>
  </Section>
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