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<Paper uid="E91-1048">
  <Title>Lexical Transfer based on bilingual signs: Towards interaction during transfer</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
4. Definition of sort hierarchies
</SectionTitle>
    <Paragraph position="0"> Sort-subsort relationships among object-sorts such as '\[TEACHER:SENSEI\] is a \[HUMAN:NINGEN\]', etc. are expressed in conventional logic by implications. However, logical implications expreSs various ontologically different relationships amoiig formulae, which have to be treated differently in translation. Sortal relationships such as these are of special importance in translation, because they l give alternative linguistic means of describing the same events/objects (a supersort gives a more vague, less specific description than the subsort). We explicitly indicate that a given implication expresses a sortal relationship, as follows. 3 We introduce a new notation. '{&lt;1 arg2&gt;,'/adv := {...}}' means that the evenffobject described by rids whole description block minus 'adv:={...)' corresponds to the arg2 of the description block immediately above, and '/adv:={...}' is convened into a predicate at the logical level Note that our treatment of 'nentoka' is essentially the same as the treatment of 'gnta 8' in the MiMe2 formalism \[van Noord, 1990\] m that it has the same defect. That h, it cannot cope with cases where more than two words which require 'raising' like 'nantcka' occur at the same level.</Paragraph>
    <Paragraph position="1"> - 277 (Sort-subsort relationships of event-sorts can also be defined in the same manner).</Paragraph>
    <Paragraph position="2">  (10) (-&gt; SUB:\[TEACHER:SENSEI\](x) SUP: \[HUMAN:NINGEN\] (x)).</Paragraph>
    <Paragraph position="3"> ('-&gt;' means logical implication) (10) shows that, if x is describable by teacher (or  sensei in Japanese), the same object can be described by a less accurate word like human. We deem the process of selecting an appropriate target expression among possible candidates as the process of locating a expression with the appropriate vagueness level.</Paragraph>
    <Paragraph position="4"> The English verb wear is a well-known example of a translationaUy ambiguous word when it is translated into Japanese. It can be translated into several different verbs including haku ('wear shoes'), kaburu ('wear a hat'), kakeru ('wear spectacles'), kiru ('wear clothes'), etc., depending on what is worn. While we have a complex expression mini-tsukeru (mi - body, ni particle, tsukeru - put on) in Japanese which preserves almost the same vagueness as wear, to use this as the translation of wear leads to an awkward translation if the material to be worn belongs to a specific sort. kutsu(shoes)-wo mini-tsukeru, for example, tends to be understood as &amp;quot;the shoes are worn on a non-standard of the body (not on the fee0&amp;quot;.</Paragraph>
    <Paragraph position="5"> The predicate \[WEAR:MI-NI-TSUKERU\] can be defined in a way similar to \[PAINT:PENKI-WO-NURU\] in (7).</Paragraph>
    <Paragraph position="7"> argument-2 of the event belongs to the sort \[SHOES:KUTSU\], then the event also belongs to \[WEAR:HAKU\].</Paragraph>
    <Paragraph position="8"> All the event-sorts related with wear in the above have the same argument structure (arity and role). But this continuity of argument structures through sorts is not necessarily guaranteed. A sort can have multiple supersorts and so the continuity of argument structures from different supersorts may conflict with each other. Furthermore, it is sometimes the case that the arities of events change between a sort and its subsorts. For example, suppose that we have two event sorts \[APPLY:NURU\] (this event-sort corresponds to the usage of apply in apply glue~paint to ...) and \[PAINT:PENKI-WO-NURU\], and that we define the latter as a subsort of the former. Then, one of the arguments in the supersort \[APPLY:NURU\] is lexically included in the subsort \[PAINT:PENKI-WO-NURU\] so that these two sorts basically have different arities. The definition of \[PAINT:PENKI-WO-NURU\] is already given as (7). The definition of \[APPLY:NURU\] is given as follows.</Paragraph>
    <Paragraph position="10"> The sort relationship between \[APPLY:NURU\] and  mean that the argument-2 in the supersort disappears in the subsort and that the argument-3 in the supersort is mapped to the argument-2 in the subsort. 'ARGi' in the CON-part is taken as referring to the argument structures of the supersorL Unspecified arguments remain unchanged between the sorts.</Paragraph>
    <Paragraph position="11"> 5. Sketch of the Transfer Phase The transfer phase is divided into three subphases as follows.</Paragraph>
    <Paragraph position="12"> (a) Transforming from thematic role structures of source sentences into schema of logical formulae(like (3))  - 278 (b) Determining logical formulae by  descending/ascending sort hierarchies&amp;quot; during this phase, inferences based on knowledge are made, and questions are asked to users, if necessary.</Paragraph>
    <Paragraph position="13"> (c) Transforming from logical formulae to thematic role structures in the target. All of these steps are performed by referring to the definitions of bilingual signs. We can index each bilingual sign by the surface word whose 'meaning': is expressed by the sign. Roughly speaking, a :word indexing a bilingual sign is either the word which appears as head in the linguistic form definitions or the word which is the value in a feature marked by '/' (like nantoka in the example \[MANAGE:NANTOKA\]).</Paragraph>
    <Paragraph position="14">  Step (a) in the above is a rather straightforward process which can be recursively performed through thematic structures. At each recursion level, the system (i) identifies the (semantic) head of the level, (ii) retrieves the vaguest possible bilingual signs for the head word (iii) transforms the local structures governed by  the head word according to the definition of the bilingual signs retrieved at (ii).</Paragraph>
    <Paragraph position="15"> Because a predicate schema of a Word may have several possible vaguest sons, step (a) produces several formulae which step (b)i tries to transform into more appropriate formulae. The processes of descending in sort hierarchies (disambiguation processes necessary for translation) are performed for different predicate schemata simultaneously (for verbs and nouns which are related to each other).</Paragraph>
    <Paragraph position="16"> Ascending the hierarchies is also: required, because the system has to instantiate all the predicate schemata contained in formula, and constraints imposed by different predicates in a schema of formulae may conflict with each other. It: may also happen that there are no corresponding target lexical items for source items, fin these cases, the system has to loosen constraints by ascending hierarchies. Therefore, step (b)i is a kind of relaxation process which tries to find the most accurate solutions satisfying all constraints. During this process, some general inference mechanisms may be invoked to infer necessary information for navigating in hierarchies and, if necessary, questions will be posed to human users.</Paragraph>
    <Paragraph position="17"> \[Estival, 1990\] also proposed using a partial order of transfer rules to choose preferred translations or prevent less preferred translations from being generated. He assumes that such a partial order of rules can be automatically computed in terms of specificities of conditions on individual transfer rules. We also use a partial order of rules (in our case, lexical transfer rules) to choose transla. tions, but the SlJecificity relationships in our system are concerned With lexical semantics and are not automatically computed but defined externally by a human based on his/her bilingual intuition. These externally imposed specificity (sort-subsort) rela. tionships also define possible paraphrasing and are effectively used:to disambiguate transfer ambiguitie s by dialogue.</Paragraph>
    <Paragraph position="18"> 6. Disambiguation of transfer ambiguities by paraphrasing Because of the explicitness of mutual relation, ships in the sort hierarchies, we can easily express an event (or object) in diversified ways in both languages. This paraphrasing facility is very useful for forming and posing appropriate questions during the transfer phase to monolingual users of the source language.</Paragraph>
    <Paragraph position="19">  As we have already seen, run can be translated into several different verbs in Japanese. Suppose that the sort \[RUN:HKSHIRASERU\] is the least specific sort which run can: describe. An event of this sort can be directly transformed into Japanese expressions by using hashiraseru. However, the direct translation is sometimes awkward if more specific lexical items exist.</Paragraph>
    <Paragraph position="20"> The system tries to descend in the hierarchy.</Paragraph>
    <Paragraph position="21"> In this example, there are two candidates: \[RUN:JIKKOOSURU\] and \[RUN:UN'EISURU\].</Paragraph>
    <Paragraph position="22"> Three ways of disambiguation by questions are possible : verbalize sort restrictions on arguments directly (ex: (16)), use the other event-sons which are not shared by both sorts such as (17), and use these two strategies (ex: (18)).</Paragraph>
    <Paragraph position="23">  (16) Is X an organization or a computer program ? (17) Does the teacher execute X or does the teacher manage X ? (18) Does the teacher execute X \[a program\] or does the teacher manage X \[an organization\] 9. 7. Conelusioln and further discussion  In this paper, we have shown that (a) our idea of bilingual signs is useful for representing the relations among lexical transfer rules which in traditional systems - 279 have not been captured explicitly. By using these relationships, we can pose appropriate questions to the user for disambiguation.</Paragraph>
    <Paragraph position="24"> (b) transfer rules which are written in our framework are basically reversible.</Paragraph>
    <Paragraph position="25"> (c) the bilingual signs connect the linguistic forms of two languages and general knowledge about events/objects denoted by them (knowledge about sort hierarchies is the simplest example of this type of knowledge) in a natural way.</Paragraph>
    <Paragraph position="26"> In our future research, we have to make it clear to what extent we can treat structural changes by bilingual signs, and on the other hand, to what extent global structural changes beyond the local restructuring by bilingual signs are necessary. We think at present that most of the global structural changes in conventional transfer systems, though necessary for natural translations, actually change the &amp;quot;meanings&amp;quot; of source sentences and should be treated by inference mechanisms external to the &amp;quot;linguistic&amp;quot; processing in translation. Though we only treat the predicates and arguments of bilingual signs, we would have to treat adjuncts as well in order to translate a whole sentence. This is related to how to control the rule application and how to ensure that all the parts of the source structure are processed. The method of formulating questions for disambiguation is still incomplete, though our method seems promising. We have to investigate what sorts of paraphrasing are really helpful for making bilingual ambiguities obvious to monolingual users.</Paragraph>
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