Lexicon-Based Methods for Sentiment Analysis - Simon Fraser ...

Computational Linguistics Volume 37, Number 2
an SO-valued noun, it is treated as an intensifier rather than as a separate SO-bearing
unit.
(5) a. The plot had huge problems.
b. They have made clear progress.
c. This is a total failure.
d. It’s an insignificant criticism.
Besides adverbs and adjectives, other intensifiers are quantifiers (a great deal of ). We
also included three other kinds of intensification that are common within our genre:
the use of all capital letters, the use of exclamation marks, and the use of discourse
connective but to indicate more salient information (e.g., ...but the movie was GREAT!). 12
In all, our intensifier dictionary contains 177 entries, some of them multi-word
expressions.
2.4 Negation
The obvious approach to negation is simply to reverse the polarity of the lexical item
next to a negator, changing good (+3) into not good (−3). This we may refer to as switch
negation (Saurí 2008). There are a number of subtleties related to negation that need
to be taken into account, however. One is the fact that there are negators, including
not, none, nobody, never, andnothing, and other words, such as without or lack (verb
and noun), which have an equivalent effect, some of which might occur at a significant
distance from the lexical item which they affect; a backwards search is required to find
these negators, one that is tailored to the particular part of speech involved. We assume
that for adjectives and adverbs the negation is fairly local, though it is sometimes
necessary to look past determiners, copulas, and certain verbs, as we see in Example (6).
(6) a. Nobody gives a good performance in this movie. (nobody negates good)
b. Out of every one of the fourteen tracks, none of them approach being weak
and are all stellar. (none negates weak)
c. Just a V-5 engine, nothing spectacular. (nothing negates spectacular)
Negation search in SO-CAL includes two options: Look backwards until a clause
boundary marker is reached; 13 or look backwards as long as the words/tags found are
in a backward search skip list, with a different list for each part of speech. The first
approach is fairly liberal, and allows us to capture the true effects of negation raising
(Horn 1989), where the negator for a verb moves up and attaches to the verb in the
matrix clause. In the following examples the don’t that negates the verb think is actually
negating the embedded clause.
(7) I don’t wish to reveal much else about the plot because I don’t think it is worth
mentioning.
12 The discourse connective but plays a role in linking clauses and sentences in a rhetorical relation (Mann
and Thompson 1988). There are more sophisticated ways of making use of those relations, but we have
not implemented them yet.
13 Clause boundary markers include punctuation and sentential connectives, including some ambiguous
ones such as and and but.
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