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<Paper uid="H90-1010">
  <Title>Two Recent Developments in Tree Adjoining Grammars: Semantics and Efficient Processing</Title>
  <Section position="2" start_page="52" end_page="52" type="concl">
    <SectionTitle>
Conclusion
</SectionTitle>
    <Paragraph position="0"> During the past year there have been two very significant developments in the area of Tree Adjoining Grammars (TAGs): synchronous TAGs and efficient processing of TAGs.</Paragraph>
    <Paragraph position="1"> A variant of TAGs called Synchronous TAGs has been developed, which is used to relate expressions of natural languages to their associated semantics represented in a logical form language. The key idea is that the logical form language itself can be described by a TAG. The two TAGs work synchronously, in the sense that the certain correspondences (links) are stated initially between the elementary trees of the two TAGs and then universal composition operations (such as substitution and adjoining) are carried out synchronously on the linked nodes of the two TAGs. Synchronous TAGs are used for language interpretation, generation and machine translation.</Paragraph>
    <Paragraph position="2"> The second development is the design of LR-style parsers for TAGs. The existence of the push down automata for context-free grammars is crucial for the development of these techniques for the parsing of context-free languages.</Paragraph>
    <Paragraph position="3"> In order to extend the LR techniques to TAGs it is necessary to find bottom-up automaton that is exactly equivalent to TAGs. This is precisely what has been achieved by the discovery of the Bottom-up Embedded Push Down Automaton (BPDA). Using BPDA the first deterministic left to right parsers for the Tree Adjoining Languages were developed.</Paragraph>
  </Section>
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