Onto.PT: Towards the Automatic Construction of a Lexical Ontology ...

8.1. Overview 133
items inside a synset are ordered according to the frequency each one of them is used
to denote the sense corresponding to the meaning of the synset. This information is
based on the annotations of SemCor (Miller et al., 1994), a sense annotated corpus.
8.1.1 Underlying lexical network
After the manual evaluation of the semantic relation extraction (see section 4.2.5),
we identified a few problems in this step. Besides minor changes in the grammars,
some lemmatisation rules were refined and some filters were added to avoid relations
between lexical items such as:
• cf, used several times in the middle of DA definitions for introducing bibliographic
references;
• transitivo, intransitivo, reflexivo, and other verb classifying words, incorrectly
extracted from Wiktionary as synonyms of verbs;
• synonymy between verbs in the gerund, often incorrect because the verb in the
gerund refers to an action that specifies the previous verb (e.g. in estender,
puxando and other examples in section 6.4.3).
These corrections resulted in CARTÃO 3.1, a new version of this resource, after
augmentation with:
• Antonymy relations from TeP 2.0, which comprise 4,276 sb-triples – 1,407 between
nouns, 1,158 between verbs, 1,562 between adjectives and 149 between
adverbs. Given that the final Onto.PT synsets are not exactly the same as
in TeP, the former antonymy relations were converted to tb-triples. For this
purpose, each sb-triple resulted in several antonymy tb-triples, each one connecting
one lexical item from the synset in the first argument with an item
from the synset in the second argument.
• Synsets from OpenThesaurus.PT, more precisely, those we could identify the
POS, which comprise 3,925 synsets – 1,971 nouns, 831 verbs, 1,079 adjectives
and 44 adverbs. As TeP was our synset-base, the former relations were converted
to tb-triples, whose arguments would later be added to TeP synsets.
For this purpose, each synset resulted in several synonymy tb-triples, each one
connecting two different lexical items in the synset.
Finally, the tb-triples connecting two lexical items not occurring in
CETEMPúblico or in TeP were discarded, unless they were extracted from more
than one resource. This can be seen as a first approach to eliminate very unfrequent
and probably unuseful words from Onto.PT. Table 8.1 shows the distribution of the
tb-triples in the lexical network used to create Onto.PT v.0.35.
8.1.2 Synsets
We recall that the synsets of TeP 2.0 were used as a starting point for creating
the Onto.PT synset-base. The assignment algorithm described in section 6.1.2 was
used to enrich TeP with the synpairs of CARTÃO, after the second resource was
augmented, as referred in the previous section. Following the experimentation described
in section 6.2, we decided to use the cosine similarity measure, with mode