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<Paper uid="C86-1031">
  <Title>Parsing in Parallel</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> This paper describes parallel model for natural language parsing and gives a design for its implementation. With the advent of parallel machines, it may be possible to view the relation of syntax and semantics in natural language parsing in a wholly new way. The approach is moving towards an application environmeat which is similar to the heterarchical sytem proposed by Winograd \[Winograd 721. Processes which control the syntactic aspects can be separated from those which control the semantic aspects in that the syntactic processes contain no semantic information themselves, but receive it by communication with the semantic processes, and vice versa. The advantage of this approach is that transparent algorithms can be written that are dedicated to only one aspect of parsing, while the desirable effects of integrating syntax and semantics can be achieved through the communication of processes. In our model we use this communication to enforce semantic constraints on the syntactic processors in order to avoid the combinatorial explosion of producing all legal syntactic possibilities.</Paragraph>
    <Paragraph position="1"> Communication between the two components is then our focus in designing a parallel parser. There seem to be three obvious levels at which communication between syntax and semantics can take place: the word level, tim phrase level, and the sentence level. We have chosen to consider communication at the phrase level rather than at either of the other two because it would be too early for the syntactic and semantic components to communicate at the word level (too little information is available at this level to help the parsing), and too late for them to communicate at the sentence level (too many syntactic parses might have already been &amp;quot;produced). How the communication between the syntactic and semantic components takes place at the phrase level will be described in Section 3.</Paragraph>
    <Paragraph position="2"> In Section 4, we design an hnplementation of this pa,'allel model for a 6-Hypereube lintel 85\] multlprocessing system, which we will have available shortly. The 6-Hypercube has sixty-four identical processors (Intel 80286's with 512K bytes of memory) and no shared memory. Although each node in the Hypereube can eventually communicate with any other node, each processor can directly communicate with only six immediately neighboring nodes. We therefore intend to limit our message passing among processors to immediate neighbors whenever possible.</Paragraph>
    <Paragraph position="3"> Like the work of Eiselt \[Eiselt 85\] on parallel inference processing, we have a pers\]~icuous assignment of natural language processing moaules to processors in the machine, although we are suggesting a parallel implementation of a parser with much more parallelism and with a clearer separation of syntax and semantics.</Paragraph>
    <Paragraph position="4"> The work on &amp;quot;massively parallel parsing&amp;quot; by Waltz and Pollack \[Waltz 85 models various components of eompreheilsion by a~tivation and inhibition of nodes of a network. A practical applieation of their approach requires massively parallel processing, currently beyond the state of l, he art in multiprocessing.</Paragraph>
    <Paragraph position="5"> We base our parallel model on the Semantic Definite Clause Grammars (SDCG) formalism of Huang Illuang 85. The SDCG evolve'd from the I)efinite Clause Gra,nmars of Pereira \[Pereira et al 80 and is described below.</Paragraph>
  </Section>
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