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<Paper uid="J83-3005">
  <Title>The NOMAD System: Expectation-Based Detection and Correction of Errors during Understanding of Syntactically and Semantically Ill-Formed Text 1</Title>
  <Section position="4" start_page="0" end_page="0" type="metho">
    <SectionTitle>
NOMAD OUTPUT:
</SectionTitle>
    <Paragraph position="0"> An enemy ship fired bombs at our ship.</Paragraph>
  </Section>
  <Section position="5" start_page="0" end_page="0" type="metho">
    <SectionTitle>
2. INPUT:
MIDWAY SIGHTED ENEMY. FIRED.
</SectionTitle>
    <Paragraph position="0"> Problem: Missing subject and objects. 'Fired' builds a PROPEL, and expects a subject and objects to play the conceptual roles of ACTOR (who did the PROPELing), OBJECT (what got PROPELed) and RECIPIENT (who got PROPELed at). However, no surface subjects or objects are presented here.</Paragraph>
    <Paragraph position="1"> Solution: Use expectations to fill in conceptual cases. NOMAD uses situational (script-based) expectations from the known typical sequence of events in an &amp;quot;ATTACK&amp;quot; - which consists of a movement (PTRANS), a sighting (ATTEND) and American Journal of Computational Linguistics, Volume 9, Numbers 3-4, July-December 1983 193 Richard H. Granger The NOMAD System firing (PROPEL) (as in other script-based understanders; see Cullingford 1978). Those expectations say (among other things) that the actor and recipient of the PROPEL will be the same as the actor and direction of the ATTEND, and that the OBJECT that got PROPELed will be some kind of projectile, which is not further specified here.</Paragraph>
  </Section>
  <Section position="6" start_page="0" end_page="0" type="metho">
    <SectionTitle>
NOMAD OUTPUT:
</SectionTitle>
    <Paragraph position="0"> We sighted an enemy ship. We fired at the ship.</Paragraph>
  </Section>
  <Section position="7" start_page="0" end_page="0" type="metho">
    <SectionTitle>
3. INPUT:
LOCKED ON OPENED FIRE.
</SectionTitle>
    <Paragraph position="0"> Problem: Missing sentence boundaries. NOMAD has no expectations for a new verb (&amp;quot;opened&amp;quot;) to appear immediately after the completed clause &amp;quot;locked on&amp;quot;. It tries but fails to connect &amp;quot;opened&amp;quot; to the phrase &amp;quot;locked on&amp;quot;.</Paragraph>
    <Paragraph position="1"> Solution: Assume the syntactic expectations failed because a clause boundary was not adequately marked in the message; assume such a boundary is there. NOMAD assumes that there may have been an intended sentence separation or clause break before &amp;quot;opened&amp;quot;, since no expectations can account for the word in this sentence position.</Paragraph>
    <Paragraph position="2"> Hence, NOMAD saves &amp;quot;locked on&amp;quot; as one clause, and continues to process the rest of the text as a new sentence.</Paragraph>
  </Section>
  <Section position="8" start_page="0" end_page="0" type="metho">
    <SectionTitle>
NOMAD OUTPUT:
</SectionTitle>
    <Paragraph position="0"> We aimed at an unknown object. We fired at the object.</Paragraph>
  </Section>
  <Section position="9" start_page="0" end_page="0" type="metho">
    <SectionTitle>
4. INPUT:
RETURNED BOMBS TO ENEMY SHIP.
</SectionTitle>
    <Paragraph position="0"> Problem: Multiple word senses of 'returned', resulting in ambiguous interpretation of action.</Paragraph>
    <Paragraph position="1"> NOMAD cannot tell whether the action here is &amp;quot;returning&amp;quot; fire to the enemy, that is, firing back at them (after they presumably had fired at us), or peaceably delivery bombs, with no firing implied.</Paragraph>
    <Paragraph position="2"> Solution: Use expectations of probable goals of actors. NOMAD first interprets the sentence as &amp;quot;peaceably delivering&amp;quot; some bombs to the ship. However, NOMAD contains the knowledge that enemies do not transfer control of weapons, information, personnel, etc., to each other. Hence it attempts to find an alternative interpretation of the sentence, in this case finding the &amp;quot;returned fire&amp;quot; interpretation, which does not violate any of NOMAD's knowledge about goals. It then infers, as in the above example, that the enemy ship must have previously fired on us.</Paragraph>
  </Section>
  <Section position="10" start_page="0" end_page="0" type="metho">
    <SectionTitle>
NOMAD OUTPUT:
</SectionTitle>
    <Paragraph position="0"> An unknown enemy ship fired on us. Then we fired bombs at them.</Paragraph>
  </Section>
  <Section position="11" start_page="0" end_page="0" type="metho">
    <SectionTitle>
5. INPUT:
OPEN FIRED.
</SectionTitle>
    <Paragraph position="0"> Problem: Lack of tense agreement between 'open' and 'fired'.</Paragraph>
    <Paragraph position="1"> Solution: Use morphological analyzer to correct tense of word. NOMAD identifies the phrase 'open fire', and assumes that past tense was intended (by default); and so constructs a phrase that correctly incorporates the tense into the phrase, to make it 'opened fire'. NOMAD then adds the inferred missing actor. (Note that were this not a known phrase to NOMAD then the tense agreement would not have been corrected at the surface level, but rather the semantic content of the two words would have contributed to a meaning representation, which would hae been used to generate a 'corrected' version of the input.</Paragraph>
  </Section>
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