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<Paper uid="P84-1024">
  <Title>Semantic Interpretation Using KL-ONE 1</Title>
  <Section position="4" start_page="102" end_page="104" type="metho">
    <SectionTitle>
3. Translation Rules
</SectionTitle>
    <Paragraph position="0"> To achieve the mapping from syntactic analysis to meaning representation, translation rules are associated with individual frames. Though the rules we give generate KL-ONE structures as the meaning representation, other translation rules could be developed for generating forms in a different target representation language.</Paragraph>
    <Paragraph position="1"> Any KL.ONE concept C representing a frame has an associated concept C' representing the main predicate of the translation. For example, the translation of SEND-CLAUSE is the concept Send-mail. Translations are stored in data attached to the frame; we label this data TRANSLATION.</Paragraph>
    <Paragraph position="2"> The translation rules themselves can be associated with individual case slots. When inheritance results in more than one translation rule for a case slot, the one originating from the most specific frame in the hierarchy is selected. 7 Suppose we are building the translation C' of a matched frame C. One common translation rule that could appear at a role R of C is (Paraphrase-as R'). This establishes the translation of the filler of R as the filler of R' at concept C'. For example, the indirect object slot of SEND-CLAUSE has the rule &amp;quot;(Paraphraseas addressee)&amp;quot; to map the translation of the noun phrase in the indirect object position into the addressee role of the Send-mail. Another rule form, (Attach-SD sf), takes a semantic function sf as an argument and attaches the translation of the constituent filling R as the filler F of sf. A example of its use in the processing of relative clauses as described in Section 6. Attach-SD differs from Paraphrase-as by having facilities to establish a role from F to C'. This automatic feature is essentially the opposite of Paraphrase.as, in that a semantic function runs from the embedded constituent to its matrix phrase.</Paragraph>
    <Paragraph position="3"> Another rule form is not a translation rule per se, but stores data with the syntactic concept representing the syntactic analysis of the phrase. The data could be checked by other (conditional) translation rules.</Paragraph>
    <Paragraph position="4"> Underlying these forms and available for more complex types of translation is a general mechanism having the form &amp;quot;source = = &gt; goal.&amp;quot; The source identifies the structure that is to be placed at the location identified by the goal. The formalism for the source allows reference to arbitrary constants and concepts and to a path through the concepts, roles, and attached data of a KL-ONE network. The goal formalism also shows a path through a network and may specify establishment of additional roles.</Paragraph>
    <Paragraph position="5"> A separate test may be associated with a translation rule to state conditions on the applicability of a rule. If the test is false, the rule does not apply, and no translation corresponding to that role is generated. The most common type of condition is (Realized-Function? role), which is true if and only if some  indexed to any role.</Paragraph>
    <Paragraph position="6"> immediate constituent fills that role in the analysis. It can be used as an explicit statement that an optional role is translated only if filled or as a way of stating that one constituent's translation depends on the presence of another role. Additional conditions are (EMPTY-RC)LE?role), which checks that role is not filled, and (ROLE-FILLER? role class), which checks that the filler of role is of type class. Since all three take a role name as argument, they may be used to state cross,dependencies among roles.</Paragraph>
    <Paragraph position="7"> Figure 3 contains some of the frames that allow for the analysis .of our example. The treatment of the pronoun and relative clause in the example sentence of Section I will be explained in Sections 5 and 6.</Paragraph>
    <Paragraph position="8">  via Abstract Case Frames Verbs can be grouped with respect to the cases they accept \[Simmons 73, Celce-Murcia 76, Gawron 83\]; likewise, groups exist for nouns. A KL-ONE syntaxonomy allows straightforward statement of common properties, as well as individually distinct properties of group members. Abstract case frames are semantic generalizations applicable across a set of the familiar sort of concrete frames. Properties common to the generalization can be defined at the abstract frames and related to the concrete frames through inheritance.</Paragraph>
    <Paragraph position="9"> The use of time modification in &amp;quot;that arrived yesterday&amp;quot; is the same as that of other verbs describing completion of an activity, e.g., &amp;quot;come&amp;quot;, &amp;quot;reach&amp;quot;, and &amp;quot;finish&amp;quot;. A general frame for clauses with these verbs can show this role. The concrete frames for clauses with verbs in this group are subconcepts and thereby accept the time modifier (see Figure 4). The concrete frames can restrict both the number and type of time modifiers, if necessary. Translation rules associated with this time role can also be restricted at the concrete frames.</Paragraph>
    <Paragraph position="10"> Some modifiers dramatically affect the translation of entire phrases, as in the partitive modifier &amp;quot;half of&amp;quot;. A description of &amp;quot;half of&amp;quot; some individual entity (as opposed to a set of entities) may not have the same distribution. For example, &amp;quot;Delete this message from my directory.&amp;quot;, makes sense, but &amp;quot;Delete half of this message from my directory.&amp;quot;, does not. This can be easily stated through an abstract frame for the basic message description specialized by two concrete frames(see Figure 5).</Paragraph>
    <Paragraph position="11"> A related case is &amp;quot;toy X.&amp;quot; The translation of &amp;quot;toy X&amp;quot; is certainly different from that of X, and their distributions may differ as well. This may be handled in a way similar to the partitive example. 8 This class of examples points out the limits of case frame systems. Other modifiers, such as &amp;quot;model&amp;quot; and &amp;quot;fake&amp;quot;, are easily recognizable. However, more complex modifiers also make the same distinctions, e.g., &amp;quot;The gun that was a fake was 8An'interesting alternative is .to show the toy modifier as an optional role on an abstract frame for object descriptions. Underneath it could be an abstract frame distinguished only by requiring the toy modification'role. All appropriate inferences associated with descriptions of toys could De associated with this concept. Frames for the basic descriptions of specific object types could be placed underneath the object description frame. These could recognize &amp;quot;toy X&amp;quot;. Our systems invoke the KL-ONE classifier after the recognition of each phrase \[Schmolze&amp;Lipkis 83\]. in this case, classification will result in identification of the phrase ss a kind of both X description and toy description allowing translation to show what is known about both without creating a &amp;quot;toy X&amp;quot; frame by hand. We have not completely analyzed the affect of this strategy on the translation system.  John's.&amp;quot;, and &amp;quot;The gun that was made of soap was John's.&amp;quot;. Viewing our semantic interpretation system as a special purpose infereoce system, it seems prudent to leave the recognition of the type of these &amp;quot;guns&amp;quot; to more general.purpose reasoners.</Paragraph>
    <Paragraph position="12"> Abstract case frames have significantly eased the development and expansion of semantic coverage within our application by helping us to focus on issues of generality and speciiicity. The new frames we add have many slots established by inheritance; consistency has been easier to maintain; and the structure of the resulting syntaxonomy has helped in debugging.</Paragraph>
  </Section>
  <Section position="5" start_page="104" end_page="104" type="metho">
    <SectionTitle>
5. Semantically Neutral Terms
</SectionTitle>
    <Paragraph position="0"> Case frames are an attempt to characterize semantically coherent phrases, for instance, by selection restrictions. In computational linguistics, selection restrictions have been applied to the constituents that are possible fillers rather than to what the constituents denote. For example, the restriction on the direct object of a SEND-CLAUSE is MESSAGE-NP, rather than messages. Problems with using such approximations in parsing are discussed in \[Ritchie 83\].</Paragraph>
    <Paragraph position="1"> For many natural language interfaces, a noun phrase's internal structure gives enough information to determine whether it satisfies a restriction, s However, there are forms whose semantic interpretation does not provide enough information to guarantee the satisfaction of a constraint and yet need to be allowed as fillers for slots. These include pronouns, some elliptical forms, such as &amp;quot;the last three&amp;quot;, and otherneutral noun phrase forms, such as &amp;quot;the thing&amp;quot; and &amp;quot;the gift&amp;quot;. This also includes some nonlexical gestural forms like the input from a display that shows where the user pointed (literally or via a mouse). We refer to all of these as sernantica//y neutra/terms. A semantic interpretation system should accept such forms without giving up restrictions on acceptable semantic categories.</Paragraph>
    <Paragraph position="2"> However, these forms cannot, in general, appear everywhere. In discussing computer mail, &amp;quot;1 sent him&amp;quot; should be considered nonsense.</Paragraph>
    <Paragraph position="3"> Bobrow and Webber \[Bobrow&amp;Webber 80b\] propose a general strategy for testing the compatibility of a constituent as a slot filler based on non-incompatibility. The current system at USC/ISI takes a conservative view of this proposal, developing the idea for only neutral reference forms. All noun phrase types displaying neutral reference are defined as instances of the concept NeutraIReference.NP. Furthermore, disjointness&amp;quot; relations are marked between the various subclasses of neutral references and those classes of explicit descriptions which have nonintersecting sets of potential references. During interpretation, when such a NeutralReference-NP is proposed as a slot filler, and that concept is not disjoint from the value restriction on the slot, it is accepted.</Paragraph>
    <Paragraph position="4"> In addition, since the slot restriction and the filler each have meaning of their own, e.g., &amp;quot;he&amp;quot; describes a human male in the computer mail domain, the translation should show the contribution of both the neutral term and the constraint on the slot. When the neutral form is qualified as a constituent by the system, both the neutral form and the selection constraint are 9Clearly, misreference also intederes with this method \[Goodman 8,3\], as does personification, metonymy and synecdoche. We propose other methods for these last phenomena in \[Weischedel 84, Weischedel 83\].</Paragraph>
    <Paragraph position="5"> remembered. When it is time to produce the translation, the translation rule for the slot applies to a concept which is the conjunction of the translations of the neutral reference form and the restriction.</Paragraph>
    <Paragraph position="6"> Part of the network that supports the translation of &amp;quot;he&amp;quot; in the example of section 1 is shown in Figure 6. Referring to Figures 2 and 3, the effect of a reference to a male where a reference to a computer-user was expected can be seen.</Paragraph>
  </Section>
  <Section position="6" start_page="104" end_page="105" type="metho">
    <SectionTitle>
6. Inter-Constituent Relationships: Relative Clauses
</SectionTitle>
    <Paragraph position="0"> In relative clauses, the constraint on the slot filled by the relative pronoun or the trace 1deg must be satisfied by the noun phrase that the relative clause modifies. In addition, the translation of the noun phrase must reflect the contribution of the use of the pronoun or trace in the relative clause. For example, in &amp;quot;Send him the message that arrived yesterday&amp;quot;, the constraint on the subject of &amp;quot;arrive&amp;quot; must be satisfied by the noun phrase of which it is a part. Further, translation must result in co-reference within the meaning representation of the value of the message role of the Arrival.mail concept and the value of the message role of the Send.mail concept (see Figure 2). This is a form of inter-constituent relationship.</Paragraph>
    <Paragraph position="1"> Our system processes relative clauses by treating the relative pronouns and trace elements as neutral reference forms (just as in the pronominal cases discussed in Section 5 and by storing the constraints on the head of the relative clause until they can be employed directly. In our example, the noun phrase &amp;quot;that&amp;quot; is seen as a Trace-NP, a kind of NeutralReference.NP. The structure assigned &amp;quot;that&amp;quot; is compatible with MESSAGE-NP and hence acceptable. On translation, the Trace-NP is treated like a neutral reference but the role and unchecked constraint are recorded, as attached data on the instantiated case frame that results from parsing the arrival clause. In the example, the facts that a Trace.NP is in the subject role and that a Message.NP is required are stored. That constraint is tested against the classification of the matrix noun phrase when the clause is proposed as a relative clause modifier. 11  If that constraint is satisfied, the fact that the relative pronoun and noun phrase co-refer is recorded. When the entire noun phrase is processed successfully, the appropriate co-references are established by performing (Attach-SD furtherconstraint) and by retrieving the translation associated with the role filled by the Trace-NP. This establishes co-reference between the concept attached by the translation rule and the : translation of the entire noun phrase. In our example, the translation of the noun phrase is made the value of the message role of the Arrival-mail.</Paragraph>
  </Section>
  <Section position="7" start_page="105" end_page="105" type="metho">
    <SectionTitle>
7. Related Work
</SectionTitle>
    <Paragraph position="0"> Our technique uses properties of KL-ONE to build a simplified, special-purpose inference engine for&amp;quot; semantic interpretation. The semantic processor is separate from both syntactic and pragmatic processing, though it is designed to maintain well-defined interaction with those components through Woods's cascade model of natural language processing \[Woods 80\]. Uniform methods include logic grammars \[Pereira 83, Palmer 83\] and semantic grammars\[Burton 77, Hendrix 78, Wilensky 80\]. Logic grammars employ a Horn-clause theorem prover for both syntactic and semantic processing. Semantic grammars collapse syntactic and semantic analysis into an essentially domain.specific grammar. Semantic interpretation is handled through unification in some evolving systems, such as PATTR-II \[Robinson 83\].</Paragraph>
    <Paragraph position="1"> Several recent systems have separate semantic interpretation components. Hirst \[Hirst 83\] uses a Montagueinspired approach to produce statements in a frame language. He uses individual mapping rules tied to the meaning-affecting rules of a grammar. Boguraev \[Boguraev 79\] presents a semantic interpreter based on patterns very similar to those of our case frames. The meaning representation it produces is very similar to the structure of our case frames.</Paragraph>
  </Section>
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