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<Paper uid="C92-4181">
  <Title>ON THE INTERPRETATION OF NATURAL LANGUAGE INSTRUCTIONS</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> In this paper, we dLscuss the approach we take to the interpretation of instructions. Instructions describe actions related to each other and to other goals the agent may have; our claim is that the agent must actively compute the actions that s/he has to perfomt, not simply &amp;quot;extract&amp;quot; their descriptions from the input.</Paragraph>
    <Paragraph position="1"> We will start by discussing some inferences that are necessary m understand instructions, and we will draw some conclusions about action representation formalisms and inference processes.</Paragraph>
    <Paragraph position="2"> We will discuss our approach, which includes an action represantation formalism based on Conceptual Structures \[Jac90\], and the construction of the structure of the agent's intentions. We will conclude with an example that shows why such representations help us in analyzing instructions.</Paragraph>
    <Paragraph position="3"> 1 Making sense of instructions Consider the following three instructions: (la) Go into the other room to get the urn of coffee.</Paragraph>
    <Paragraph position="4"> (tb) Before you pick it up, be sure to unplug it.</Paragraph>
    <Paragraph position="5"> (lc) When you bring it back here, carry it carefully with both hands.</Paragraph>
    <Paragraph position="6"> Let's consider (la). To understand this instructiou, an agent must find the connection between ttle two actions a--go into the other room, and \[3--get the urn of coffee.</Paragraph>
    <Paragraph position="7"> The infinitival to alerts the agent to the fact that a contributes to achieving /3. General knowledge about physically getting objects requires that the agent move to the place where the object is located; therefore, the agent will infer that the (most direct) connection between these actitms has go into the other room fulfilling this requiremenL However, this is not enough. An assumption needs to be made for such connection to go through, namely, that the urn is in the other room.</Paragraph>
    <Paragraph position="8"> This example shows that to make sense of instructions, an agent must engage in the active computation of the action(s) to be executed, and cannot simply &amp;quot;extract&amp;quot; all such information from the input. This differentiates our work from others', as we will discuss shortly.</Paragraph>
    <Paragraph position="9"> Another important point that arises from (la) is that the relation contributes holding between c~, described in the matrix clause, and t, described in the purpose clause 1, can be specilied either as generation or enablement, as a study of naturally occurring purpose clauses \[Di 92,'1\] shows.</Paragraph>
    <Paragraph position="10"> Generation was introduced by \[Gol70\]. Informally, if action ,~ generates action t, we can say that fl is executed hy executing c~. An exmnple is Turning on the light hy flipping the switch.</Paragraph>
    <Paragraph position="11"> Enablement. Following \[Po186\] and \[Bat901, action cr enables action fl if and only if an occurrence of c, brings about conditions necessary for the subsequent performance of ft. In Unscrew the protective plate to expose the box, &amp;quot;unscrew the protective plate&amp;quot; enables &amp;quot;taking the plate off&amp;quot; which generates &amp;quot;exposing the box&amp;quot;. In \[Po186\], it is shown that these two relations are necessary to model action descriptions conveyed by Natural Language. We would like to add one further observation: such relations allow us to draw conclusions about action execution too. Tbis is quite useful since we do have to execute (it., animate) the input iustractions, as our work is taking place in the context of the Animation from Natural Language (AnimNL) project at the University of Pennsylvania \[WBD*91I.</Paragraph>
    <Paragraph position="12"> As far as generation is concerned, while two actions arc described, only a, the generator, needs to be performed; instead, if c~ etmbles t, after executing ~r, fl still needs to be executed. In fact, if cx enables t, cr bas to begin, but not necessarily end, before/3.</Paragraph>
    <Paragraph position="13"> I We am using the term purpose clauses to informally designate robordinate clausel -- such as those introduced by to -- that express the igenI'l pmpog in executing the action delcdbed in the matrix clause. The usage of the term purpose clause in the lyntactic literature ii sOmewhat different--~ee \[JonS5l.</Paragraph>
    <Paragraph position="14"> ACI'ES DE COLING-92, NANTES. 23-28 Ao~r 1992 l I 4 7 PROC. OF COLING-92, NANTES, AUG. 23-28, 1992 In both eases, the goal/3 also constrains the interpretation and / or execution of c~. An example of this as regards generation is (2) Cut the square in half to create two triangles.</Paragraph>
    <Paragraph position="15"> The only action to be performed is cut the square in half.</Paragraph>
    <Paragraph position="16"> However, there is an infinite number of ways to cut a square in half: the goal create two triangles restricts the choice to cut the square along one of the two diagonals.</Paragraph>
    <Paragraph position="17"> We turn next to the second instrnctiQn (lb), Observe that the agent understands pick up to be part of the sequence that achieves get the urn of coffee. This is not warranted by the preposition before: if (lb) were Before you ruin it, be sure it's unplugged, the agent clearly shouldn't infer that ruin it is part of getting the urn! This shows that in before c~, /3, the action e~ is not necessarily part of achieving a certain goal, even if/~ is, As far as (lc) goes, the agent has to understand that bring it back here is part of achieving getting the urn; that carry it carefully with both hands generates bring it back here, provided that carry it carefully with both hands is augmented with the destination back here. Notice that the action description carry it carefully with both hands is fairly complex, sporting two modifiers in addition to the traditional arguments of agent and patient,</Paragraph>
  </Section>
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