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<Paper uid="W04-2608">
  <Title>Decision Trees for Sense Disambiguation of Prepositions: Case of Over</Title>
  <Section position="4" start_page="0" end_page="7" type="evalu">
    <SectionTitle>
4 Evaluation
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    <Paragraph position="0"> An evaluation of the two decision trees was conducted manually by using 500 sentences containing over produced by the British National Corpus (BNC). Among the 500 instances of over, there are 382 prepositional uses. Among the remaining, fifty six (56) instances are those meaning more than or excess, which are located characteristically immediately before a quantity word or phrase. Examples are given below:  (20) (a) We have visited over 90 schools and reached 36,000 pupils.</Paragraph>
    <Paragraph position="1"> (b) Anything over this amount is, basically  liable to inheritance tax at 40%.</Paragraph>
    <Paragraph position="2"> Twenty (20) instances of over are adjectives meaning completion, as in: (21) My war seemed to be over.</Paragraph>
    <Paragraph position="3"> Fifteen (15) instances are those used as adverb, an example of which is illustrated: (22) ... , and read the list over and over again. The sentences including over and over again are repeated twice in the data because of the two instances of over in the phrase. The data contains six such sentences, resulting in 12 counts of over and over again. Seven (7) instances are used right before the to-prepositional phrase or toward-prepositional phrase, as in: (23) She went over to the Cookery and Refreshments Tent, but ...</Paragraph>
    <Paragraph position="4"> The distinction between such instances of over as in (21), (22) and (23) on one hand and prepositional uses on the other could be made by purely syntactic treatments because of their different syntactic characteristics. Most of instances meaning more than or excess as illustrated in (20) are morphologically distinguishable from prepositional uses, because most of quantity nouns or noun phrases after over refer to something other than time. However, among the total 56 instances implying more than or excess, thirteen (13) quantity phrases refer to time. As such a phrase is composed of the same structure (over + noun/noun phrase) as an over-prepositional phrase, this appears to cause difficulty. But a careful examination of these constructions reveals otherwise. Such a phrase of quantity occurs in a syntactic position requiring a noun phrase, as illustrated in: (24) a. ... after 12 years of living in those conditions, I would probably want to die myself.</Paragraph>
    <Paragraph position="5"> meanings features of the- null b. ... I had heard nothing about my family for over ten years.</Paragraph>
    <Paragraph position="6"> c. ... since they were written over 10 years ago, ...</Paragraph>
    <Paragraph position="7"> All these phrases of quantity are located either after a preposition such as for, in, within and after or in an adverbial phrase ending with such a word as ago and late. Therefore, a good syntactic parser should be capable of distinguishing these quantity phrases with over from over-prepositional phrases.</Paragraph>
    <Paragraph position="8"> Two instances of over are found in quoted phrases in sentences. Eighteen (18) sentences are either incomplete (as in PUB REFURBISHMENTS - OVER THE LIMIT and Over the wrenched?) or difficult to parse (as in First part over, second part starts and ... moved hard over in the direction of the spin).</Paragraph>
    <Paragraph position="9"> With the non-prepositional uses and anomalous instances of over in the data aside, the next topic of discussion is about the three hundred and eighty two (382) prepositional uses found in the data. Among the 382, eighty seven (87) instances of over are parts of phrasal verbs or idiomatic phrases. Among the 87, fifty (50) instances of over do NOT govern a prepositional phrase, as illustrated below: (25) a. And Dicky can take over as a footman.</Paragraph>
    <Paragraph position="10"> b. She went over to fetch a cup of coffee.</Paragraph>
    <Paragraph position="11"> c. I explain the position to the daughters and hand Mum over to them.</Paragraph>
    <Paragraph position="12"> d. ... there is no reason for their practiced eyes to cloud over when ...</Paragraph>
    <Paragraph position="13"> Thirty seven (37) instances of over are parts of phrasal verbs governing an over-prepositional phrase. Examples are given below: (26) a. Go over the launch failure procedures after any long lay-off from flying.</Paragraph>
    <Paragraph position="14"> b. ... and failed promptly to hand over detainees to the police - ...</Paragraph>
    <Paragraph position="15"> With the lexicon containing sufficient information on such phrasal verbs, there would remain two hundred and ninety five (295) prepositional uses of over, the meanings of which must be distinguished. The decision trees proposed in this paper succeeded in determining the meanings of two hundred and seventy six (276) instances, and failed to interpret the meanings of nineteen (19), resulting in a precision of 93.5 percent. However, if the system does not recognize phrasal verbs, the value of the precision will be lower.</Paragraph>
    <Paragraph position="16"> Some more problems and possible solutions are discussed here. It would be difficult to determine the use of over when the verbs in the sentence are conjoined, as in We finished our coffee and watched the seagulls whirling and shrieking over the harbour in the spring sunshine. When the verb shriek is categorized as a psychological verb, the use of over will be interpreted as over_about, which is a wrong interpretation in this case. The decision tree in Figure 1 will fail to recognize the following example because a search for the use of over_means requires the semantic feature +definite: ... the cruel, brutal voices that bellow over loudhailers about injustice .... The Complement of over, loudhailers is not preceded by the definite article the, which is a requirement for identifying over_means. The feature +definite may be dispensable for sense identification, but it will be needed when the decision tree is used for generation, because the definite article often occurs in this type of prepositional phrase as in over the phone. A difficulty in determining whether a noun refers to a physical object or an abstract entity causes a problem. The example ... with the lying motto over its gate ... is hard to analyze. The use in this example is not over_about, but over_locus. With the correct interpretation of motto either as a physical object or a statement, the decision tree could lead to the right meaning of over. If motto refers to a physical object, the use of over is over_locus, whereas if it is not, the use is over_about. In the example such as The drag of the cable over one wing can make ..., the deverbal noun drag must be properly parsed as the Head of over in order to interpret the meaning of over correctly.</Paragraph>
    <Paragraph position="17"> Based on the assumption (a) that a syntactic parsing is successful, (b) that the over in phrasal verbs are recognized beforehand, and (c) that verbs and nouns are properly categorized into classes, the two decision trees could identify the meanings of most prepositional uses of over in the corpus. In addition, information on whether the Head event refers to a durational event or not would enable the tree to distinguish between over_about and over_because. Table 5 gives a breakdown of the instances of over found in the data (PP stands for prepositional phrase): over included in or used as No.</Paragraph>
    <Paragraph position="18"> PP (over not in phrasal verbs) 295</Paragraph>
  </Section>
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