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<Paper uid="P00-1022">
  <Title>A Computational Approach to Zero-pronouns in Spanish</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
2 Detecting zero-pronouns
</SectionTitle>
    <Paragraph position="0"> In order to detect zero-pronouns, the sentences should be divided into clauses since the subject could only appear between the clause constituents. After that, a noun-phrase (NP) or a pronoun that agrees in person and number with the clause verb is sought, unless the verb is imperative or impersonal.</Paragraph>
    <Paragraph position="1"> As we are also working on unrestricted texts to which partial parsing is applied, zero-pronouns must also be detected when we do not dispose of full syntactic information. In Ferrandez et al. (1998), a partial parsing strategy that provides all the necessary information for resolving anaphora is presented. That study shows that only the following constituents were necessary for anaphora resolution: co-ordinated prepositional and noun phrases, pronouns, conjunctions and verbs, regardless of the order in which they appear in the text.</Paragraph>
    <Paragraph position="2"> H1 Let us assume that the beginning of a new clause has been found when a verb is parsed and a free conjunction is subsequently parsed.</Paragraph>
    <Paragraph position="3"> When partial parsing is carried out, one problem that arises is to detect the different clauses of a sentence. Another problem is how to detect the zero-pronoun, i.e. the omission of the subject from each clause. With regard to the first problem, the heuristic H1 is applied to identify a new clause.</Paragraph>
    <Paragraph position="4">  In this particular case, a free conjunction does not imply conjunctions2 that join co-ordinated noun and prepositional phrases. It refers, here, to conjunctions that are parsed in our partial parsing scheme. For instance, in sentence (1), the following sequence of constituents is parsed: np(John and Jane), verb(were), freeWord3(late), pp(for work), conj(because), pron(they), verb(over-slept ) Since the free conjunction porque (because) has been parsed after the verb llegaron (were), the new clause with a new verb durmieron (over-slept) can be detected.</Paragraph>
    <Paragraph position="5"> With reference to the problem about detecting the omission of the subject from each clause with partial parsing, it is solved by searching through the clause constituents that appear before the verb. In sentence (1), we can verify that the first verb, llegaron (were), does not have its subject omitted since there appears a np(John and Jane). However, there is a zeropronoun, (they)[?], for the second verb durmieron (over-slept).</Paragraph>
    <Paragraph position="6"> (2) Pedroj vio a Anak en el parque. [?]k Estaba muy guapa (Peterj saw Annk in the park. [She][?]k was very beautiful) When the zero-pronoun is detected, our computational system inserts the pronoun in the position in which it has been omitted. This pronoun will be resolved in the following module of anaphora resolution. Person and number information is obtained from the clause verb. Sometimes in Spanish, gender information of the pronoun can be obtained when the verb is copulative. For example, in sentence (2), the verb estaba (was) is copulative, so that its subject must agree in gender and number with its object whenever the object can have either a masculine or a feminine linguistic form (guapo: masc, guapa: fem). We can therefore obtain information about its gender from the object, guapa (beautiful in its feminine form) which automatically assigns it to the feminine gender so the omitted pronoun would have to be she rather than he. Gender information can be obtained from the object of the verb with partial  parsing as we simply have to search for a NP on the right of the verb.</Paragraph>
  </Section>
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