Dissertação de mest., Natural Language Processing and Human Language Technology, Univ. do Algarve, 2009This dissertation describes and proposes a set of linguistically motivated rules for zero
anaphora resolution in the context of a natural language processing chain developed for
Portuguese. Some languages, like Portuguese, allow noun phrase (NP) deletion (or zeroing)
in several syntactic contexts in order to avoid the redundancy that would result from
repetition of previously mentioned words. The co-reference relation between the zeroed
element and its antecedent (or previous mention) in the discourse is here called zero
anaphora (Mitkov, 2002). In Computational Linguistics, zero anaphora resolution may be
viewed as a subtask of anaphora resolution and has an essential role in various Natural
Language Processing applications such as information extraction, automatic abstracting,
dialog systems, machine translation and question answering. The main goal of this
dissertation is to describe the grammatical rules imposing subject NP deletion and referential
constraints in the Brazilian Portuguese, in order to allow a correct identification of the
antecedent of the deleted subject NP. Some of these rules were then formalized into the
Xerox Incremental Parser or XIP (Ait-Mokhtar et al., 2002: 121-144) in order to constitute a
module of the Portuguese grammar (Mamede et al. 2010) developed at Spoken Language
Laboratory (L2F). Using this rule-based approach we expected to improve the performance
of the Portuguese grammar namely by producing better dependency structures with
(reconstructed) zeroed NPs for the syntactic-semantic interface. Because of the complexity
of the task, the scope of this dissertation had to be limited: (a) subject NP deletion; b) within
sentence boundaries and (c) with an explicit antecedent; besides, (d) rules were formalized
based solely on the results of the shallow parser (or chunks), that is, with minimal syntactic
(and no semantic) knowledge. A corpus of different text genres was manually annotated for
zero anaphors and other zero-shaped, usually indefinite, subjects. The rule-based
approached is evaluated and results are presented and discussed
