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<Paper uid="P95-1013">
  <Title>Compilation of HPSG to TAG*</Title>
  <Section position="3" start_page="92" end_page="93" type="intro">
    <SectionTitle>
2 Background
</SectionTitle>
    <Paragraph position="0"> As the target of our translation we assume a Lexicalized Tree-Adjoining Grammar (LTAG), in which every elementary tree is anchored by a lexical item (SAJ88).</Paragraph>
    <Paragraph position="1"> We do not assume atomic labelling of nodes, unlike traditional TAG, where the root and foot nodes of an auxiliary tree are assumed to be labelled identically. Such trees are said to factor out recursion. However, this identity itself isn't sufficient to identify foot nodes, as more than one frontier node may be labelled the same as the root. Without such atomic labels in HPSG, we are forced to address this issue, and present a solution that is still consistent with the notion of factoring recursion.</Paragraph>
    <Paragraph position="2"> Our translation process yields a lexicalized feature-based TAG (VSJ88) in which feature structures are associated with nodes in the frontier of trees and two feature structures (top and bottom) with nodes in the interior. Following (VS92), the relationships between such top and bottom feature structures represent underspecified domination links. Two nodes standing in this domination relation could become the same, but they are necessarily distinct if adjoining takes place. Adjoining separates them by introducing the path from the root to the foot node of an auxiliary tree as a further specification of the underspecified domination link.</Paragraph>
    <Paragraph position="3"> For illustration of our compilation, we consider an extended HPSG following the specifications in (PS94)\[404ff\]. The rule schemata include rules for complementation (including head-subject and head-complement relations), head-adjunct, and filler-head relations.</Paragraph>
    <Paragraph position="4"> The following rule schemata cover the combination of heads with subjects and other complements respectively as well as the adjunct constructions. 2 2We abstract from quite a number of properites and use the following abbreviations for feature names: S-----SYI&amp;quot;/SEM, L~LOChL, C~ChT, N-L----NON-LOChL, D-----DTRS,  We assume a slightly modified and constrained treatment of non-local dependencies (SLASH), in which empty nodes are eliminated and a lexical rule is used instead. While SLASH introduction is based on the standard filler-head schema, SLASH percolation is essentially constrained to the HEAD spine.</Paragraph>
    <Paragraph position="5">  The percolation of SLASH across head domains is lexically determined. Most lexical items will be specified as having an empty SLASH list. Bridge verbs (e.g., equi verbs such as want) or other heads allowing extraction out of a complement share their own SLASH value with the SLASH of the respective complement. 3 Equi and Bridge Verb</Paragraph>
  </Section>
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