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<Paper uid="W04-2608">
  <Title>Decision Trees for Sense Disambiguation of Prepositions: Case of Over</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Prepositions have been studied from a variety of perspectives. The syntactic status has been probed by such linguists as Jackendoff [77], Emonds [85], Rauh [93] and Pullum and Huddleston [02]. Cognitive theorists have paid attention to the polysemous nature of prepositions and explored the conceptual relationships of the polysemy, often proposing the graphical mental images (Lakoff and Johnson [80], Brugman [81, 88], Herskovits [86], Langacker [87], Tyler and Evans [01]). Pragmatic aspects of prepositions have been studied by such scholars as Fauconnier [94] and Visetti and Cadiot [02]. The deictic properties of spatial prepositions have been examined by Hill [82], while the geographical information provided by them was an interest of computational research (Xu and Badler [00], Tezuka et al [01]). A practical study of the usage of prepositions was carried out for the purpose of teaching English as a second language (Wahlen [95], Lindstromberg [97], Yates [99]).</Paragraph>
    <Paragraph position="1"> In the fields related to natural language processing, prepositional phrase attachment has been a topic for research for quite a long time, and in recent years, the problem was explored with a neural network-based approach (Sopena, LLoberas and Moliner [98]) and with a syntax-based trainable approach (Yeh and Valin [98]).</Paragraph>
    <Paragraph position="2"> Although past research has revealed various aspects of prepositions, to my knowledge there is not much semantic research of prepositions available for computational use, which requires a vigorous formalization of representing the semantics.</Paragraph>
    <Paragraph position="3"> A recent semantic study of prepositions for computational use is found in Voss [02], with a focus on spatial prepositions. Spatial prepositions are divided into three categories according to which one of the two thematic meanings between place and path they acquire when they are in argument, adjunct and non-subcategorized positions of particular types of verbs. The semantics of spatial prepositions dealt with in Voss [02] is not lexical but thematic.</Paragraph>
    <Paragraph position="4"> The present study places more focus on the lexical meanings of prepositions rather than on the thematic meanings because it is intended for use in machine translation (MT), where the meaning of a sentence, a phrase or a lexical entry of a source language must be preserved in the target language, even though it may take a different syntactic form in the source and target languages. The preservation of meaning is even more important at an Interlingua-based MT, because meaning is a medium of translation between source and target languages.</Paragraph>
    <Paragraph position="5"> The current research deals with the prepositional uses of over, but not with the uses of over in different syntactic categories such as the use as adjective (as in The initial test is over), as part of a phrasal verb (as in He handed over his notes to me), as part of an idiomatic phrase (as in She said it over and over) and as a modifier of a quantity (as in over forty years ago). These uses could be identified in terms of their syntactic characteristics. On the other hand, the prepositional uses are grouped under the same syntactic category, but exhibit different meanings in different semantic contexts, requiring semantic treatments as well for the disambiguation of the senses.</Paragraph>
    <Paragraph position="6"> This paper examines the meanings of the prepositional uses of over, identifies the semantic contexts, and proposes two decision trees for interpreting the different meanings. The second section will divide the prepositional uses of over into two groups according to which one of the two functional units between Head and Complement is likely to identity the meanings. It will also bring into light the semantic features of the Head and Complement components that make the interpretations of the uses possible. The third section will discusses the two decision trees proposed in this paper, and the fourth section gives an evaluation of the trees, before concluding this paper.</Paragraph>
    <Paragraph position="7"> 2 Meanings of the prepositional uses Prepositional uses of over could be divided into two groups: those whose meaning is likely to be identified by the Complement noun phrases and those that need semantic information in the Head components. The noun phrase following a preposition is the Complement of the preposition, whereas the verb, verb phrase, noun or noun phrase governing a preposition or a prepositional phrase is the Head.</Paragraph>
    <Paragraph position="8"> 2.1 Over identified by its Complement Unlike the uses of over governed or required by the Head verb or noun, over the weekend in They have been unwell over the weekend can appear with almost all semantic classes of verbs, as illustrated below.</Paragraph>
    <Paragraph position="9">  (1) a. I heard over the weekend of a terrible fuss.</Paragraph>
    <Paragraph position="10"> b. He thought about it over the weekend and accepted.</Paragraph>
    <Paragraph position="11"> c. Talks with bankers were taking place over the weekend.</Paragraph>
    <Paragraph position="12"> d. It probably began over the weekend of March 27.</Paragraph>
    <Paragraph position="13"> e. His father had died over the weekend.</Paragraph>
    <Paragraph position="14">  f. American diplomats arrived here over the weekend.</Paragraph>
    <Paragraph position="15"> The phrase over the weekend appears with a sensation verb (1a), a cognition verb (1b), an occurrence verb (1c), an aspectual verb (1d), a change of state verb (1e) and a movement verb (1f). This suggests that over the weekend is not required by a particular semantic class of verbs. At the same time, it is likely to be identified from the semantic features of the Complement noun phrase, which denotes a definite period of time in discourse during which an event takes place. This use of over is called over_during because it is similar to the usage of during.</Paragraph>
    <Paragraph position="16"> On the other hand, over can appear with the Complement denoting an indefinite period of time in discourse, as in: (2) Altogether, tutorials take place over a period of about twenty-four weeks.</Paragraph>
    <Paragraph position="17"> The Complements of over_during in (1) and this use share the semantic characteristic by referring to time of duration, but differ in that the former refers to a specific period of time in discourse while the latter only a length of time over which an event continues. This use is named over_duration.</Paragraph>
    <Paragraph position="18"> Another use that denotes a length of time is as follows: null (3) Skimming a chapter for its main ideas may be done over coffee.</Paragraph>
    <Paragraph position="19"> Unlike the other two we have seen above, the Complement does not refer directly to a space of time, but still the prepositional phrase implies an interval of time, in particular the duration of drinking coffee. Like the use of over_duration, the Complement does not refer to a definite period in discourse because the semantic function is to indicate a length of time. The Complement in this type is characterized by its meaning denoting meal or drink as well as by referring to a nonspecific meal or drink in discourse. This use is termed over_coffee.</Paragraph>
    <Paragraph position="20"> Like the three uses we have seen above, the following is also likely to be identified by the syntax and semantics of the Complements: (4) We heard the news over the radio at lunch break.</Paragraph>
    <Paragraph position="21"> The phrase over the radio indicates a means of hearing the news. The Complement in this use is often a sequence of the definite particle the followed by a noun denoting a device of communication such as radio and telephone. Although the Head verb or noun tends to refer to a communicative act, as this use takes a Complement with distinctive semantic features, it should belong to this group. It is called over_means.</Paragraph>
    <Paragraph position="22"> Another use of over that could belong to this group is the following: (5) You can go all over the place.</Paragraph>
    <Paragraph position="23"> The Complement denotes a place in many cases, but sometimes a physical object, and this use of over is always preceded by all. Although the Head verb or noun tends to denote movement, this use also appears with other types of predicates, as illustrated below:  (6) a. Paint all over the studio.</Paragraph>
    <Paragraph position="24"> b. He is known all over Europe.</Paragraph>
    <Paragraph position="25"> c. Tapes crash all over my desk.</Paragraph>
    <Paragraph position="26">  The following is a list of the prepositional uses of over that are likely to be identified by the semantic features of the Complements: Table 1. Uses identifiable by the Complements The following is a list of the features identifying the uses of over by the Complements.</Paragraph>
    <Section position="1" start_page="0" end_page="0" type="sub_section">
      <SectionTitle>
2.2 Over identifiable by its Head
</SectionTitle>
      <Paragraph position="0"> Unlike the prepositional uses of over that are likely to be identified by the semantics of the Complements alone, the following are the uses that would require the semantic information of the Heads as well for identification. null 2.2.1 Head denoting a physical event When the Head of over denotes movement and the Complement a place or a physical object, the over-prepositional phrase indicates a place above which and across which an object moves, as given below:  (7) a. The bullet goes flying over my head and lands in the field behind me.</Paragraph>
      <Paragraph position="1"> b. Safe, efficient movement over snow and ice is impossible without suitable crampons.</Paragraph>
      <Paragraph position="2">  The prepositional phrase indicates a path over which an object moves, and therefore it is termed over_path. Another use of over indicating place is illustrated by the following example:  (8) After spreading her napkin over her lap,  Alice began to eat.</Paragraph>
      <Paragraph position="3"> The prepositional phrase implies a place on which or above which an object sits. In this example, her napkin is placed over her lap. This use is called over_locus. The Head refers to an event denoted by a verb or noun belonging to the put verb class (cf. Levin [93]) while the Complement a place or a physical object.</Paragraph>
      <Paragraph position="4"> In addition, this use is also used with a Head verb denoting the presence of an object as in: (9) An occasional loop stays over the needle after knitting the row.</Paragraph>
      <Paragraph position="5"> Indeed, this use is more complex than it appears. In a sentence with the BE verb, we find the following examples: null (10) a. My painting is over the sofa.</Paragraph>
      <Paragraph position="6"> b. There were no taps over the sink.</Paragraph>
      <Paragraph position="7"> The use of over in this construction is tricky because it is difficult to distinguish from the use of over meaning about, as illustrated below: (11) The disagreement here is over the substitutability of assets.</Paragraph>
      <Paragraph position="8"> As complex as such, this construction would need a special syntactic treatment separately from other uses. That is, in this construction, the subject noun phrase is the Head of over, and thus the semantics of the subject along with that of the Complement must be examined for proper identification.</Paragraph>
      <Paragraph position="9"> Another special syntactic treatment should be given to an over-prepositional phrase modifying a noun phrase or noun, as in: (12) I can just see the light over the door from where I'm standing.</Paragraph>
      <Paragraph position="10"> In this example, the Head is a noun phrase the light and the Complement the door. Since the Head is a physical object, and the Complement a physical object, the use of over is over_locus, which means that the Head entity is located at the Complement entity. When the Head in this nominal modifier construction denotes an event or state, as in his return flight over the North Sea, there would be no special treatment required. It can be treated in the same manner as when the verb is the Head. A special pragmatic knowledge should come into play in the use of over_locus. It is not straight-forward, in fact, to determine this use only by the semantics of the Head and Complement. In every construction for this use, there is a possibility that the prepositional phrase indicates the meaning of across, as illustrated in: (13) a. His apartment is over my flat.</Paragraph>
      <Paragraph position="11"> b. His apartment is over the river.</Paragraph>
      <Paragraph position="12"> Although both sentences have the same syntactic structure, they have noun phrases referring to different places. meanings examples over_during Over the next decade a global approach is going to be essential. null over_ duration Their flowers appear over several weeks in summer.</Paragraph>
      <Paragraph position="13"> over_coffee There's a lot for you to talk about over lunch.</Paragraph>
      <Paragraph position="14"> over_means Lewd songs are sung over the microphone.</Paragraph>
      <Paragraph position="15">  over_manyparts null The dog ran all over the parking lot.</Paragraph>
      <Paragraph position="16"> meanings features of  As an apartment can be located over a flat in the real world, the meaning of the prepositional phrase in (13a) implies a place where an object is located (i.e. over_locus). On the other hand, as an apartment is usually not located above the river, the meaning in (13b) implies a place across where an object is situated. This latter use of over is named over_across. To distinguish between over_locus and over_across requires more than the semantics of the Head and Complement components. The distinction would require encyclopedic world knowledge. Without having such a knowledge system, this paper will treat both over_locus and over_across in the same manner except for the fact that the default choice between the two is over_locus due to the much higher frequency in its use.</Paragraph>
      <Paragraph position="17">  There are four uses of over whose Head denotes a non-physical event. The use we examine at first is illustrated in the following examples:  (14) a. Marcos ruled over the Philippines for 20 years.</Paragraph>
      <Paragraph position="18"> b. He has considerable control over her activities.</Paragraph>
      <Paragraph position="19"> c. He had one huge advantage over everyone else.</Paragraph>
      <Paragraph position="20">  The Head denotes an act of control or having more power. Among verbs of such a class are preside, rule, win, excel, dominate and tower. This use metaphorically implies that an object is above the other object in terms of power.</Paragraph>
      <Paragraph position="21"> The next use of over is found in: (15) A general dictionary was preferred over the domain-specific dictionaries.</Paragraph>
      <Paragraph position="22"> The Head is a verb or noun denoting selection. Among them are prefer, choose, select, favor and the deverbal nouns. This use is called over_prefer. The noun counterpart of a verb in this class, however, should be treated with care, because the over may imply the meaning of about, as in  (16) They are organized to allow the users choice over what to see, in the correct time sequence.</Paragraph>
      <Paragraph position="23"> What is going on is that over_prefer requires two entities in order to choose one over the other. When there are no such two entities between which to choose, as in (16), the meaning of over turns out to be that of about. On the other hand, when there are, the meaning is over_prefer, as illustrated in: (17) One of the most basic freedoms anywhere is the right to peace, and the choice of quiet over noise.</Paragraph>
      <Paragraph position="24"> Since verbs of this family are transitive verbs requiring the Object, when the sentence contains both the Object noun phrase and an over-prepositional phrase, the mean null ing of over_prefer obtains. In the proposed decision tree involving this use, the Head is limited to a verb, not a noun because of this syntactic freedom of a noun in this category. (To handle cases involving such a noun, a question as to the number of the arguments governed by the noun must be added.) A final discussion is about two uses named  over_about and over_because. The use of over_because is illustrated in the following examples: (18) a. Teachers were suspended over war posters. b. He quit over a bribery scandal.</Paragraph>
      <Paragraph position="25">  The over-prepositional phrase implies a cause of the event or state. It seems that the meaning of over_because requires a punctual event as in (18a) and (18b). On the other hand, over with durational verbs in this class gives rise to the meaning of over_about, as illustrated by the following examples: (19) a. He talked over the issue for three hours. b. Disputes over authorship are fiercely fought.</Paragraph>
      <Paragraph position="26"> c. There is growing concern over his illness. d. They thought over all the possible errors. The Head of this use denotes events of communication (such as hear and chat), agree events (such as disagree and fight), psychological events or states (such as worry, cry and agonize) and cognitive events or states (such as think and know).</Paragraph>
      <Paragraph position="27"> Table 3 shows the uses of over the meanings of which are identified mainly by the semantics of the Head.</Paragraph>
      <Paragraph position="28">  contribute to identifying the meanings of the prepositional uses of over.</Paragraph>
      <Paragraph position="29"> meanings examples over_path Let the eye move over it.</Paragraph>
      <Paragraph position="30"> over_across The gallery is over the front door. I admit that part of the ball was over the line, but that's not enough.</Paragraph>
      <Paragraph position="31"> over_locus Jessica sprayed paint over the furniture. over_control It was Prime Minister Yoshida who presided over Japan's post-war economic boom.</Paragraph>
      <Paragraph position="32"> over_prefer I would prefer coffee over tea.</Paragraph>
      <Paragraph position="33"> over_about He's mulling over an offer from NBC to star in his own series.</Paragraph>
      <Paragraph position="34"> At the counter, a couple puzzled over which lottery numbers to choose.</Paragraph>
      <Paragraph position="35"> over_ because Teachers were suspended over war posters.</Paragraph>
      <Paragraph position="36"> He quit over a bribery scandal.</Paragraph>
    </Section>
  </Section>
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