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

104 Chapter 6. Thesaurus Enrichment
POS
Noun Verb Adjective
Synpairs 61,025 28,895 34,844
In TeP 15,183 (22.5%) 13,891 (48.1%) 11,930 (34.2%)
|C| = 0 14,902 (22.1%) 615 (2.1%) 2,659 (7.6%)
|C| = 1 8,902 (13.2%) 960 (3.3%) 3,365 (9.7%)
|C| > 1 28,414 (42.2%) 13,429 (46.6%) 16,890 (48.5%)
|C| 4.30 8.49 4.34
Table 6.4: Coverage of the synpairs by TeP.
where synpairs have a second chance of being assigned to a synset, this time using
the same similarity measure, but with a higher threshold, σ = 0.35. The previous
value obtained the best precision in the mode All and, once again, against all human
references. The second iteration intends to integrate unassigned synpairs, in which,
after the first iteration, there is high confidence on the assignment to a synset.
After the assignment stage, 37,767 noun, 14,459 verb and 20,310 adjective synpairs
were assigned to, at least, one TeP synset. Of those, respectively 35,247, 14,246
and 19,595 were assigned during the first iteration and 2,520, 213 and 715 during
the second. Table 6.5 presents examples of real assignments and the iteration where
they were accomplished 2 .
It. Synpair Synset
1 st {alimentação, mantença} {sustento, alimento, mantimento, alimentação}
1 st {escravizar, servilizar} {oprimir, tiranizar, escravizar, esmagar}
1 st {permanente, inextinguível} {durador, duradoiro, duradouro, durável, permanente,
perdurável}
2 nd {cortadura, cortadela} {golpe, cisão, cortadela, rasgue, corte, incisura, rasgo,
cortadura, incisão}
2 nd {reificar, substancializar} {realizar, coisificar, efetivar, efeituar, consumar, efectivar,
efetuar, concretizar, reificar, hipostasiar, substantificar}
2 nd {encorajante, entusiasmante} {empolgante, entusiasmante, galvanizante, galvanizador}
Table 6.5: Examples of assignments.
6.4.3 Clustering for new synsets
In order to discover new synsets, the clustering procedure in section 6.3 was applied
to the remaining synpairs, with θ = 0.5. Before clustering, we analysed some properties
of the synonymy networks they form. After clustering, some of the obtained
results were evaluated manually.
The discovered clusters were integrated in the enriched TeP, following the integration
procedure described in section 6.3, using a threshold µ = 0.5, empirically
defined. Not many synsets were however merged. More precisely 81 noun, 16 verb
and 29 adjective clusters were merged to existing synsets. The rest of the clusters
were added as new synsets.
2 Intentionally, no translations are provided because, if translated, most of the provided examples
would not capture the essence of this task.