Unni Cathrine Eiken February 2005

5 Final remarks
5.1 Is a parser vital for the extraction process?
An initial assumption during the development of the method in this thesis was that it was of high
importance to found the extraction method on a syntactic parse of the text collection. As the
reader will recall, the reasons for this assumption were elaborated in chapter 3 and will therefore
not be discussed further here. However, as a means of evaluating the extraction method, the
texts in the text collection were processed using the Oslo-Bergen Tagger (OBT 2005). This is a
part of speech (POS) tagger which among other options offers the user a syntactic
disambiguation of the input text. The texts were POS tagged using the web version of the tagger
and structures corresponding to subject-verb-object relations were manually extracted from the
output. This yielded a list of 169 structures, 26 of them with pronouns. The structures were
extracted using a quite rudimentary method; for example no differences were made between
active and passive versions of the same predicate. This resulted in a list featuring exactly the
problematic issues discussed in chapter 3; the arguments were represented (and subsequently
structured) not according to thematic roles, but merely according to their syntactic roles in the
sentence. As a result, the list did not reflect characteristic arguments of the different predicates
to the same degree as the EPAS list did. The list of the POS-based structures is available in
Appendix F.
Consider the FCA diagram in Figure 7 below. Figure 7 shows part of the FCA diagram created
for the POS-based structures; the section of the diagram with the argument politi (police) as
starting point is highlighted. When comparing this figure to the corresponding figure for the
EPAS list (Figure 5 in section 3.6.4), it is quite clear that the POS-based list is significantly less
generalisable. There are no clear groupings of arguments which display specific behaviour
through their combination with a certain subset of predicates. Because formal subjects of both
active and passive sentences are realised as first arguments in this extraction, it is hardly
possible to group arguments into groups of semantically related words based on their
distribution. As can be seen from the diagram, politi co-occurs with both sykepleiestudent
(student nurse) and bilfører (driver), as well as other, more relevant, arguments.
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