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<Paper uid="C94-2154">
  <Title>TIIE CORRECT AND EFFICIENT IMI)LI~',MI,N.\[A&amp;quot; '~ TION OF' APPI\[()PRIATENESS SPECIFI(:ATIONS FOR TYPF;D FlgATURI&amp;quot; STRUCTUR\]~,S</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> Unification lbrmMisms ma.y be either untyped (DCC~s, PATR-II, 1,F(;) or typed (npsG). A m~L,ior reason for adding types to ~ forma,lism is to express restrictions on fea.ture cooccurences a.s in (;l's(:: \[5\] in order to rule out nonexista.nt tyl)es of objects. For example, there a.re no verbs which have the \[km.ture +R. The simplest way to express such restrictions is by mea.ns of a.n a.ppropria.teness pa.rtim flmction Approp: Type x Feat ~ Type.</Paragraph>
    <Paragraph position="1"> With such a.n a.pl)rol)riatleness specifica.tion lrla.tly Sllch restrictioi,s may be expressed, though no restrictions involving reentrancies ma.y be expressed.</Paragraph>
    <Paragraph position="2"> In this pal)er, we will first in SS2 survey the range of type eonstra.ints tha.t ma.y be expressed with just a. type hiera.rchy and *'\]'he resea.rch pl'eS(!lllL('d ill |,his; paper was pay tia.lly sponsored hy '\[kfilprojekt B4 &amp;quot;(;onsl.rahH.s on Grammar fl~r Efficient Ck:neration&amp;quot; of the Soi,der forschungsbereich 340 of the Deutsche \[&amp;quot;orschungsgemeinscha, ft. &amp;quot;VVe would also like to thank 'l'hilo GStz for helph,l comments ou thc ideas present.ed here. All mistakes a.rc of collrsc our OWll.</Paragraph>
    <Paragraph position="3"> IKI. Wilhehnstr. 113, |)-721174Tfilfi,,ge,, (lerma.ny, {rig,King} g'~sfs.n phil.uni-I uebingen.de. a.n N)propria.teness specification. Then in ~3, we discuss how such type cons|fronts linty be mainta.ined under unification as exemplilied in the na.tura.1 language D~rsing/generation system '.l'ro\]l \[7\]. 1 Unlike previous systems such as ALl,:, Troll does not employ a.ny type infereneing, inste~M, a, limited amount of named disjunction (\[1 1\], \[12\], \[6\])is introduced to record type resol u tion possibilities. The a.lnount of disjunction is a.lso kept small by the technique of unlilli,g described in \[9\]. This strategy a.ctua.lly ma.inta.ins apl)ropri~tteness conditions in some ca.ses in which a. type inferencing stra.tegy would fa.il, l)'inMly, in SS4, we discuss the possibilities for genera lizillg this a.pl)roa.ch to ha.ndle a bro~Mer r~tnge of constra.ints, including constraints inw)lving reentran cies.</Paragraph>
  </Section>
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